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Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium (1958)

Chapter: Session II - Methods for Controlling Ambient Illumination

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Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
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Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
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Page 34
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 35
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 36
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 37
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 38
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 39
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 40
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 41
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 42
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 43
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 44
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 45
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 46
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 47
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 48
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 49
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 50
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 51
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 52
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 53
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 54
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 55
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 56
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 57
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 58
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 59
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 60
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 61
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 62
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 63
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 64
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 65
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 66
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 67
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 68
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 69
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 70
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 71
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 72
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 73
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 74
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 75
Suggested Citation:"Session II - Methods for Controlling Ambient Illumination." National Research Council. 1958. Illumination and Visibility of Radar and Sonar Displays: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/9554.
×
Page 76

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SESSION 11: METHODS FOR CONTROLLING AMBIENT ILLUMINATION CHAIRMAN Dr. Henry A. Imus THE RATIONALE FOR USE OF CONTROLLED WHITE LIGHT IN RADAR AND SONAR SPACES Carroll T. White, U. S. Navy Electronics Laboratory SOME APPLICATIONS OF CONTROLLED WHITE LIGHTING Fred G. Henry, U. S. Navy Electronics Laboratory A BROAD-BAND-BLUE LIGHTING SYSTEM FOR RADAR APPROACH CONTROL CENTERS: EVALUATIONS AND REFINEMENTS BASED ON THREE YEARS OF OPERATIONAL USE Conrad L. Kraft, Laboratory of Aviation Psychology, The Ohio State University RELATIONS AMONG DARK ADAPTATION, THE SPECTRAL CHARACTER OF ILLUMINATION, AND THE VISUAL TASK John L. Brown, Acceleration Laboratory, U. S. Naval Air Development Center EFFECTS OF CERTAIN PRE-EXPOSURE VARIABLES ON DARK ADAPTATION John A. Hanson, Institute for Applied Experimental Psychology, Tufts University MAKING RADAR INDICATORS USEFUL IN HIGH AMBIENT ILLUMINATION J. R. Roeder, Air Arm Division, Westinghouse Electric Corporation 33

The Rationale for Use of Controfiec' White Light in Raciar and Sonar Spaces CARROLL T. WHITE, U.S. Navy Electronics Laboratory Summary Special lighting systems may be categorized in terms of general area i/Zumir~ation and localized illumination. Among the advantages of locally controlled lighting are its flexibility in complex systems and its elimination of reflections from displays. Principles for location of lamps and selection of type of illumina- tion are reviewed. Emphasis is placed on the use of white light. Polarized white light is specially advantageous for the illumina- tion of cathode-ray tubes. Work on specialized lighting systems at the Navy Electronics Laboratory has been directed at the general problem of critical lighting needs and not at any particular type of installation. This may help to explain some of the differ- ences between our concepts of light control and those which have evolved else- where. The first work along this line involved the selective spectrum lighting sys- tems, with which most of you are familiar. These systems represented an attempt to utilize the unique characteristics of certain illuminants and filters in order to achieve increased illumination with little interference with the displays. Exper- ience with these systems soon revealed distinct limitations and restricted appli- cability, so we began looking for other techniques that would better fit the needs of the many types of installations in which radar or sonar displays are involved. Out of this continuing study, our present concept of lighting has evolved; it is basically the idea of localized light control. This paper will attempt to describe the merits of such an approach. Regardless of the specific details, all the special lighting systems fall into one of two categories: general area illumination or localized illumination. One goal of the general area illumination approach is to achieve as nearly as possible the ideal interior lighting - fairly even over the entire area, with no high con- trasts between different sections. The localized lighting approach is based on an entirely different premise i.e., that each critical position in an area should be supplied with the proper quantity and quality of light for the job to be per- formed at that position. The overall illumination is considered to be of secondary importance. This does not mean that lighting is provided only at the scope con- soles. Properly controlled luminaires are installed for desk surfaces, equipment racks, and panels, and for safe passage throughout the area. One of the most important features of a locally controlled lighting system is its flexibility. It can be applied to every kind of installation from a single-scope sonar room to a complex installation where a number of different types of jobs are being done. In a complex installation, it is possible to supply each man with widely different amounts of light, according to his needs, without interfering - 34

with others who are working nearby. No single level of illumination can be chosen in the proper range for all the activities which go on in a complete situation. Locally controlled lights must be introduced into spaces for those tasks demanding much reading, writing, or repair of equipment. What has been said concerning the flexibility of a locally controlled lighting system has implied the use of various levels of white light, but it should be clear that any type of illuminant could be used at any particular station' or no illum- inant at all if it is found that it is operationally better to have a particular display in relative darkness. By means of a locally controlled lighting system, it is possi- ble to meet the special requirements of any display without penalizing those who must work in the vicinity of the display. Whenever light is introduced into an area, we face the problem of first- surface reflections from the glass or plastic masks covering the display scopes. If care is not taken, these reflections degrade the display beneath them. In a properly designed, localized lighting system, specular reflections are avoided by the careful placement and louvering of the luminaires. Reflections sometimes present a real problem for a system already installed, but can be handled without difficulty if the lighting is considered during the design of the system. The problem is different for a general area lighting system. If the illumina- tion level of an entire area is raised to an appreciable amount, specular reflections cannot be avoided. Major glare sources can be eliminated by the careful place- ment and louvering of the overhead luminaires, but reflections of objects (in- cluding the operator) will still be present to some degree. Since most plans for ares lighting systems have called for limited spectrum illumination it has been suggested that the operators wear special goggles which do not Pass wavelengths within the Illuminating spectrum, thereby e~m~nat~ng all first-surface reflec- tions. This would certainly do the job, but it is probably not very practicable. First-surface reflections can also degrade other visual displays, such as status boards and summary plots. This effect and the scope reflection problem make it quite evident that we cannot achieve successful illumination by arbitraril placing overhead luminaires throughout an area. The proper placement and control of light sources is a problem to be faced in both the general area lighting and the locally controlled lighting systems. Once it has been decided that a locally controlled lighting system should be developed, the next questions are: where should the lights be placed, and what type of lights should they be? Whenever a light source is introduced at a given work position, it must (a) supply an adequate level and distribution of light, (b) not "spill over" into adjacent work spaces unnecessarily, and (c) not be a source of direct or indirect glare either for the worker in that position or for other workers in the area. To meet these requirements, care must be taken in the choice of a luminaire, the placement of the luminaire, and in the design of the supplementary louver. 35-

For work positions where no CRT displays are involved, there is no real problem. Since a great deal of reading, writing, troubleshooting' etc., must be done at these positions white light is the logical choice. The variety of color coding encountered in printed material and electronic circuitry is the major reason for this decision. The level of illumination is determined by the particular tasks to be performed. It is usually desirable to provide supplementary illumination for those por- tions of the area not adequately lighted by spill-over from the work positions. Additional illumination should include a series of lights placed near the floor to define and illuminate safe pathways through the area. In the floor design itself, pathways can be indicated by light tiles set against a dark background. A well- designed system should also include lights installed specifically for the conven- ience of maintenance personnel. The majority of these can be located within the consoles and racks themselves. They can easily be arranged so as to be of full benefit to the technician and only a minor distraction for the operating per- sonnel. The problem of providing illumination for those positions at which CRT displays are located is most critical, but it must not be divorced from the light- ing needs of the system as a whole. There are a number of ways in which we may introduce light around a scope without having light reach the display itself. Limited spectrum illumination of the console, with a filter over the scope which rejects that illumination, is the best known approach. The use of a polarized light source with a second polarizer over the scope is also a possibility. Another method is the use of focused white light, arranged so that panels and writing surfaces are illuminated and relatively little light reaches the scope itself. Still another approach, which has been suggested, is the use of a special wire mesh as · In ~ ~'rr. ~ ~ · 1 1 1 a covering for the scope. vvlth ordinary overneao 1uminaires, the mesh prevents light from reaching the display plane. And, if all else fails, there is always the hood. Each of the above techniques serves the purpose of keeping extraneous light from reaching the display screen, but it would be futile to try to apply any one technique in every situation. There are good arguments pro and con even for the scope hood. Admittedly, it is too restrictive for most purposes, but there are undoubtedly situations where display characteristics might demand extreme measures of this kind. It is a basic tenet of the locally controlled lighting concept that any of the special light control techniques may be used whenever necessary. The light control principle utilizing polarized white light) is probably the most widely applicable of all. Since the polarizing filter is not color selective, it may be used with any phosphor or mixed-phosphor display. At the same time, the operator can be supplied with white light so that he may be more effective in those phases of his work other than scope-watching itself. For a particular phosphors a colored filter may be available which will transmit a higher per- centa~e Of the light. emitted hv that r~hosohor than would. be transmitted by a - -rid Or- - 0 o~ ~^ ~ 0~ ~ ~ ~--~~ r--~r~ ~~ ~White, C. T. Polarized-light illumination of radar and sonar spaces and comparison with limited spectrum methods. U. S. Navy Electronics Laboratory, 1956, Report 669. 36

polarizer. The crucial question, however, is not how much light is or is not trans- mitted, but rather whether or not this has any practical effect on the performance of the operator. In this regard, we must realize that there are factors other than the filter transmittance which enter the picture; among these are, for instance, the dynamic characteristics of the display itself and the overall duties of the man who must work at that display position. The first of these would determine the latitude the operator has in increasing the light output of the display' and the second would indicate what compromises might be justified from the point of view of the entire system. In conclusion' I would like to summarize our point of view in regard to the problem of the illumination of critical areas: ( 1 ~ This problem is of much greater importance than is usually thought, and it should be an integral part of systems planning and design. (2) The wide variety of tasks to be performed in such an area leads us to favor a system which supplies each working position with the quantity and quality of light most appropriate to it rather than a system which represents a compromise with the needs of every position. ~ 3 ~ Whenever possible, white light should be used. Full spectrum illumination best meets the needs for most work positions, including those with CRT displays. There may be situations where the display characteristics may require some other type of light control. Even in these situations the total job of the man at that position must be consid- ered before a decision is made7 and any decision made for one position should not dictate what is done at any other position. (4) Finally, we do not believe that there is any one solution to this problem. Any attempt arbitrarily to specify what is to be done could be a real disservice. What is needed is for us to learn more about the characteristics of the various means of light control, and for us to deter- mine the situations in which each might be most suitable. In this way, we will be able to supply the system designer with those techniques he needs in order to make appropriate illumination an integral part of that system. --37

Some Applications of Controlled White Lighting FRED G. HENRY, U.S. Navy Electronics Laboratory Summary- This paper describes the use of controlled white lighting in two specialized installations where CRT displays are employed. The advantages of using controlled white light for in- installatzons of this type are: ( 1 ~ the reduction of distracting first- surface reflections from CRT displays; (2) good color discrimina- tion for various displays; (3) controlled variation of brightness values in the visual field, depending on the operators' require- ments; (4) adequate localized lighting which does not degrade scope displays, through the use of linear and circular polarizers; (5) nominal installation costs; and (6) flexibility of the con- trolled white lighting. The technique lends itself both to designing systems prior to construction and to altering operating areas which require lighting improvement. This report describes the application of controlled white light in two spec- ialized installations. The first is a Navy radar air traffic control center in which the lighting has been an important part of system planning. The second is a ground control approach (GCA) mobile radar van in which an experimental lighting scheme was implemented to improve the operator's visual environment. The objective for each installation was to design a lighting system which was operationally efficient, flexible, and economical to apply. Under a Bureau of Ships problem assignment, the Navy Electronics Lab- oratory (NEL) has provided technical assistance during design and implemen- tation of the NAS Miramar Radar Air Traffic Control Center (RATCC). Tech- nical assistance by NEL on this problem has, in the main, been confined to de- signing a lighting system. Figure 1 shows the general configuration of the RATCC, the major equip- ments involved, and the room dimensions. The system includes sixteen PPI displays of which thirteen are radar indicators, two are NTG projection displays, and one is an Iatron (not shown). Twenty air-controllers comprise the normal daytime watch. Among the general requirements of the lighting system for RATCC, the two rather specific lighting objectives were that the system be designed so that each member of the RATCC team has brightness relationships in his visual field which allow optimal, or near optimal, performance over prolonged watch periods; and that the system design be adaptable to other RATCCs with minimum difficulty and expense. On the basis of extensive experimentation with various lighting techniques, the laboratory concluded that both of these objectives could be met by using controlled white lighting In essence. this technique draws upon two basic prin- ciples of light control. the first principle is that light can be effectively controlled through the use of linear and circular polarizers. Radar consoles, illuminated by _ _ ~--~ 38

a polarized source, have a second circular Polaroid filter placed over the CRT display. The second filter is rotated by 90° with respect to the source polarization. Almost all incident light on the radar scope is thus cancelled. ^^'^ ~/~ ~ Fig. 1. General configuration of NAS Miramar RATCC, including equipments and room dimensions {ft). Dotted outline represents opaque wall map. Since only polarized light is cancelled by a correctly oriented Polaroid filter over the radar display, it is necessary to minimize the presence of stray, uncon- trolled light. This is accomplished through application of the second principle: light can be effectively controlled through manipulating the absorption and re- flection characteristics of surfaces in the visual field. This lighting principle is applied throughout RATCC but is especially effective at all operating stations, including radar indicators. The second principle is the basis of localized illumina- tion wherein the light flux is restricted to a well-defined region through the aid of black lattice louvers and spectral characteristics of surfaces in the visual field. Careful application of these two principles has met the lighting requirements of controllers at fixed positions and of supervisors who must move freely in RATCC. To aid in implementing these principles at the major operating positions, two mockup studies were undertaken. One was concerned with the application of localized light at the flight progress consoles; the others with the application of controlled white light at the radar consoles. From these studies it was possible to specify optimal lighting components including a fluorescent lamp, a special lattice louvered device, and a mounting assembly which positions the luminaire for optimal results. When properly grouped, these components apply to both flight progress consoles and radar consoles. Flight progress consoles Three requirements influenced the lighting installation at the flight progress console: ( 1 ) sufficient lighting for all aspects of the operator's seeing task, (2) - 39

localizing illumination to prevent spill-over on the adjacent radar operators, and (3) minimizing glare from the flight-strip display area so that adjacent radar operators are not affected by peripheral "hot-spots." In satisfying the first requirement, it was necessary to employ a luminaire which would provide good lighting for several specific seeing tasks. These tasks include the viewing of a fli~ht-strip display area, multichannel communication box, desk space, and clock. In order to obtain an optimal light source for tne operator's work space, several luminaire configurations were tested, both custom- built and commercially available. A desirable feature of the luminaire we decided to use is its adaptability to various types of lattice louvers. This was considered important in satisfying the second requirement of directional light control. Light control at the flight progress console is essential in view of its close proximity to adjacent radar indicators. Louvered assemblies were easily designed to fit the luminaires. Lattice louvers have been effective in minimizing stray light which might otherwise adversely affect scope visibility. Two longitudinal plates of the louvered assembly provide a sharp light cut-off in front of the operator, while the close spacing of the trans- verse plates provide an even sharper cut-off point at the console sides. Thus, 6 ft-c of illumination was measured on the extreme edge of the flight progress board in contrast with less than 0.10 ft-c of light spill-over at the adjacent radar . . posltlon. To satisfy the third requirement, action was taken to minimize glare from the flight progress display. Single flight strips currently used by the CAA are printed on light green or buff lusterless paper. The light reflectance from these strips ranges up to 63 per cent. The controller, who sits directly in front of this display, is in a comfortable visual environment since the greatest portion of his visual field is uniformly illuminated. On the other hand, the radar operator im- mediately adjacent to this position is faced with a somewhat different visual environment. The region to which he attends may absorb as much as 80 per cent of the incident light and therefore appear much darker than the flight progress strips for the same amount of incident light. Relatively bright surfaces in the radar operator's peripheral visual field are distracting and result in general visual discomfort. In an effort to minimize the peripheral glare from the flight progress board, the laboratory has experimented with black flight progress strips. A white blueprint pencil makes clearly legible mares on the black paper, which has a light reflectance value of 5.8 per cent. By using the black strips, a 91 per cent reduction in peripheral glare is achieved. Radar consoles There were two main considerations in optimizing lighting at the radar indicators. The first was the efficient application of Polaroid filters over both the illuminating source and the radar displays. The louvered assembly employed in the fluorescent luminaire was designed to accommodate a strip of linear Polaroid. The polarizer is seated on the top of the louvered assembly. A 1/16-in. _40

lip around the edge of the louver prevents the polarizer from shifting and fixes its plane of polarization with respect to the luminaire. Since the luminaire is supported by a rigid mounting arm, accidental bumping of the fixture will not change the axis of polarization. Light intensity at each operating position is also fixed only an on-off switch is available to control the light source. Efficient application of circular Polaroid filters was similar for each of thirteen radar displays. This was accomplished, for example at the medium- range indicators, by removing the scope bezel and placing the filter below the implosion shield. The Polaroid filter was then rotated so that its axis of polariza- tion was crossed to that of the light source. After reassembly, the polarizer was locked in place and its relatively soft surface was protected from scratching by the Lucite implosion shield. Since these two surfaces were not sealed, there was a slight tendency for dust to collect between the Polaroid filter and the bottom side of the implosion shield. The best solution to this problem is found in com- mercially available Polaroid glass laminates. These laminates are a suitable sub- stitute for the conventional transparent plastic implosion shields and are con- siderably more scratch resistant. The second consideration was optimal placement of the luminaire over the radar indicator. Figure 2 shows diagrammatically the approximate light pattern produced by the luminaire in relation to the operator. It should be noticed that the luminaire is mounted so that lamp reflections are not visible to the operator, either seated or standing. Furthermore, the lattice louver protects the operator from an otherwise annoying glare source when he looks up to throw a channel switch. Similarly, the louver eliminates stray light on the operator and distract- ing first-surface reflections of face and clothes. Environ merit Other factors affecting the general visual environment of the RATCC in- clude the finishing of floor, ceiling, and walls, and the lighting of large vertical displays. The floor covering for most of the RATCC room is a dark asphalt tile, which was installed before serious consideration was given to optimal interior finishing. Ideally, the entire floor could have been much lighter. As a com- promise solution, aisles were designated and the dark tile in these sections of the floor was replaced with off-white asphalt tile. Lighting of the aisles is provided by several low-output directional lamps that illuminate the walk space in front of the major operating positions. Low-intensity, localized floor lighting can be sufficiently well controlled so that it presents no problems to the radar operator. At the same time, floor lighting increases the overall brightness of the room, thus providing a more pleasing environment. The ceiling and the walls are covered with Celotex tile in a matte finish which reduces the effects of stray light. The ceiling, which tends to be visible as a first-surface reflection in the CRT displays, was painted black; any stray light striking this black matte surface is almost completely absorbed. The walls were painted with a nonreflecting forest green, since they are less likely to reflect light on the CRTs to the extent of affecting scope visibility. -41

1 I I 1 / l \\ \\ D \? ~ B \ ~ \ _ ~ ' ( \ fig. 2. Elements of light control at radar console: {A) Light ray strikes filter, specular reflections directed downward, {B) path of light from display, (C) extent of the penumbra, {D) representation of theoretical limit of the light beam, as de- termined by the depth/width ratio of the louver cell. \ \ Two vertical displays have also been considered in the overall RATCC lighting scheme. The first is a large opaque wall map showing the local operating area. This map is 18 ft in length by 8 ft in height. The achromatic background with shades ranging from dark grey through white provides a suitable field for displaying multicolored, magnetic, visual aids. Color coding is used to designate the federal airways, navigation aids, and various holding patterns and approach routes. The map is illuminated by two 96-in. fluorescent lamps mounted in tan- dem. The light from this source is controlled by louvers which confine light to the immediate vicinity of the map and do not affect the radar display. Proper positioning of the luminaires and louvers assures uniform distribution of light over the entire map surface and does not interfere with scope visibility. The second display is a clear-plastic' edge-lighted, status board designed for posting weather information. All external light sources are shielded from this surface in such a way that no direct reflections are visible to any personnel utilizing the data presented. The edge lighting of the plotting board also raises the brightness level of that portion of the room. -42-

While lighting of the areas described has been largely as a result of func- tional considerations, action has also been taken to raise the subjective light level of the entire center. In so doing, the under-lighted appearance sometimes associated with directional lighting systems has been greatly reduced. Our work in lighting the Miramar RATCC has included control over the selection, design, and location of luminaires and over the reflectances and textures of the entire environment and its contents. The plan has resulted in viewing conditions suited to the most stringent seeing tasks in a radar air traffic control center and higher, more psychologically satisfying, light levels for personnel in noncritical areas. GCA lighting The remainder of this paper is concerned with an experimental lighting installation designed to improve illumination in standard GCA trailers of the Gilfillan and Bendix types. This example demonstrates the flexibility of using controlled white lighting in areas where initial systems planning did not ade- quately consider the operator's visual environment. Traditionally, the darkened operating area has been considered necessary for maintenance of optimum CRT viewing conditions. There is good reason to believe, however, that the GCA controller is actually at a disadvantage when required to operate his radar display in a darkened area. There are four main objections to the dark operating conditions for GCA consoles. The first objection is that GCA controllers frequently come into the trailer from bright ambient conditions with the result that it requires at least three minutes for them to dark- adapt to the trailer interior. The second objection is glare or halation from the radar displays. To compensate for the high contrast between the bright video display and the usually much darker scope surrounding, operators frequently turn on supplementary light to reduce the contrast. Unfortunately, the only available auxiliary light sources are flashlights, which are difficult to control and sometimes shine directly into the scope face. The third objection is lack of sufficient illumination to carry out emergency maintenance. Under operating conditions, if a failure occurs the technician must either work in the dark or use a poorly controlled, auxiliary light source which may be inadvertently directed at the controller's scope. The fourth objection is lack of sufficient illumination on various knobs and switch controls. Operators frequently use an auxiliary illuminating source to establish positive identification of a particular control. The objections cited indicate the nature of the lighting deficiencies in both the Bendix AN/MPN-5 and the Gilfillan AN/CPN-4 mobile radar sets. The elimination of these difficulties required raising the level of illumination in both trailers, especially at the operating positions. The NEL cross-polarized lighting system appeared to satisfy the objections and to be otherwise functionally suit- able. Accordingly, two experimental lighting installations were set up and studied under operational conditions. Controlled white lighting at the operating positions in the GCA trailer solved satisfactorily nearly all the shortcomings of the visual environment. _43 ~· ~ret ~

A Broacl-Bancl-Blue Lighting System for Raclar Approach Control Centers: Evaluations anc' Refinements Basec' on Three Years of Operational Use CONRAD L. KRAFT, The Ohio State University Laboratory of Aviation Psychology Summary The broad-band-blue lighting system utilizes the visible spectrum selectively to illuminate radar approach control centers. Shorter visible wavelengths from 400 to 540 me provide room illumination. Filters over cathode-ray tubes absorb this energy and transmit visible energy from the phosphor in the region from 540 to 700 mu. The system permits one operator to utilize light from a radar display to good advantage while another has adequate room illumination for other tasks. Results from three years of operation have been favorable. Lighting of radar rooms is a current problem. The illumination require- ments of the two groups of people who must jointly use a radar center (operations personnel, and maintenance and other personnel) differ radically. The require- ment of both groups cannot be met by ordinary lighting procedures. Under ordinary conditions, light needed by supporting personnel for maintenance de- stroys most of the information available on phosphor cathode-ray tubes and greatly diminishes the ability of the radar operator's eye to use the information that remains. The sensitivity of the human eye to light of different frequencies, and the frequency characteristics of the light energy emitted by the phosphor of a CRT, must be fully understood to appreciate the nature of the radar room lighting problem. White room light, while it provides the illumination needed by supporting personnel, attenuates the visibility of a CRT signal. The visible signal-to-noise ratio of the CRT signal is decreased because the room light affects the ambient visible noise level in two ways: ( 1 ) the room light excites the phosphor surface of the CRT, and (2) the room light is mirrored on the front surface of the CRT and so adds spectral and diffuse reflections to the phosphorescence to "wash out" the signal. This effect is illustrated in Fig. 1. The figure on the left shows a signal of an intensity typical of a 3-see-old signal on a P7 phosphor, Viewed against a background luminance characteristic of the video noise of a CRT ire an unlighted room. The figure on the right shows the same signal "lost" in the noise level resulting from the use of 2 ft-l of white room light. In addition to the signal-to-noise ratio of the radar signal, another factor that determines the "visibility" of a signal is the sensitivity of the observer's eyes. The intensity level at which the room is illuminated is a primary determiner of this sensitivity to faint signals. As shown in Fig. 2, the lower the intensity of the room light, the greater becomes the sensitivity of the human eye. Figure 2 illustrates the amount of increase in the sensitivity of the eye to radiant energies at different wavelengths as a function of successive reductions in the luminance level of the room over five log units; these are data for a white adapting light of 2360° K about the color of sunlight 25 min after sunrise. 44

Fig. 1. Illustration of the effect of white room light on signal-to-noise ratio of a 3-see-old signal on a P7 cathode-ray tube. c >`- . _ a> c D a) C J a) D O ._ o ,= LO > _ No Room Light Visible Noise o Fig. 2. Amount of radiant energy :- "~E-' required to obtain equal apparent JO Cr3 3 brightness of a small target as a ,- o-~~4 function of the wavelength of light =. ~~5 emitted from the target with adap- -~ ~7 ing luminance the parameter.] ~ ~ -is Noise = 0.74 Ft. Lamberts Two F. cot Lamberts of White Room Light 4oo 500 600 700 Wavelength in Millimicrons Level of Adoptotion in I. Ft. Lamb~rts -1.0 . -0.1 . -0.01 -0.001 . -0.0001 . ~0.00001 Color of the illumination also contributes to the visual sensitivity level of the eye. Data recently reported by Hurvich and Jameson' indicate that when the eye is adapted to a given level of blue (short wavelength) light, its sensitivity to light ire the orange-red (long wavelength) end of the visible spectrum is some- what enhanced over its sensitivity after adaptation to a white light of the same brightness level of the blue adapting light. The broad-bard-blue lighting system takes advantage of both of these effected ~ The most efficient way to resolve the problem of radar room lighting is the application of the well known principle of frequency sharing. An idealized solution would be to allocate to the scope observer those wavelengths necessary to transmit to his eye all the energy of the CRT phosphorescence resulting from target returns, while keeping the background luminance of the CRT at a min- imum level of electronic (video) noise. The remaining wavelengths would be allocated to supporting personnel for use as ambient room illumination. The optimum division of the visible spectrum for these two purposes depends on the frequency spectrum of the phosphor emission, which varies with each specific type of phosphor display; it depends also on the spectral sensitivity of the human eye, which varies as a function of the level and spectral distribution of the ambient light that is permitted to enter the eye. . ~Judd, D. B. Basic correlates of the visual stimulus. In S. S. Stevens (Ed.), Handbook of Ex- perimental Psychology. Wiley, 1951, p. 820. 2Hurvich, L. M., and Jameson, D. Special sensitivity of the fovea. II: Dependence on chro- matic adaptation. Journal of the Optical Society of America, 1953, 43, 552-559. ::Kraft, C. L., and Fitts, P. M. A broad-band-blue lighting system for radar approach control centers. Proceedings of the 33rd meeting of the Armed Forces-NRC Vision Committee, Nov. 12-13, 1953. 4Kraft, C. L., and Fitts, P. M. A broad-blue-band lighting system for radar traffic control centers. Wright Air Development Center, 1954, Technical Report 53-416. -45

Optimum frequency sharing, or the selective use of the visible spectrum, Is the basic principle on which the broad-band-blue lighting system is designed. The filters that are used represent the best available practical compromise in terms of selective transmission and sharpness of cutoff for a radar room using several types of phosphors. The short-wavelength cutoff for the room illumina- tion filter has been placed at 400 me so that no ultraviolet wavelengths are in- cluded in the room light. The wavelengths from 400 to 540 me are used for room illumination. This relatively broad band of frequencies provides an almost white light (it has a soft blue appearance) and, in addition, is broad enough to preclude the possibility of any difficulty in focusing the eyes (accommodation). As men- tioned above, this relatively wide band used for room illumination serves a second purpose in making invisible the initial blue flash of the P2, P7, and P19 phosphors (see the shaded portion of these three curves in Fig. 31. If an intense blue flash is visible, subsequent sensitivity of the eye to light is lowered, and signal visibility is affected so that the persistence of the phosphor seems to be decreased. .~ ~ `eaY ~ phosph robe Glanced Fig. 3. The spectral distribution of the ambient room illumination of the 6road- band-blue system and the effect of the scope filter on the emission spectra of different phosphors. Thus, the broad-band-blue system not only makes it possible for scope ob- servers and other personnel to carry on their work simultaneously, but it also meets the requirements of radar centers where a variety of phosphor types are used simultaneously. For example, the six types of CRTs shown in Fig. 3 can all be accommodated by this system. An orange-yellow scope filter used with the system is indicated in Fig. 3 as a curved surface dividing each spectrum into "visible" and "invisible" portions. The visible portion is the area to the right under the filter curve and appears nearest the reader. This area represents the wavelengths passed by the filter and visible to the radar scope operator as targets on the display. 46

The room-illumination filter is shown as the bell-shaped curve in the first plane of the three-dimensional diagram. The first plane is replicated in Fig. 4 to show the mutually exclusive transmission curves of the room-light and scope filters. Although the over-all "color" associated with the room light is bluish, this filter passes violet, blue, and some green to make up the desaturated light. Very little of the energy of these wavelengths is passed by the yellow-orange scope filter, so no fluorescence of the CRT is created by the room light. That is, the "photometric noise level" of the scope remains practically at zero except for the internal noise arising from the electronic system. Since there is no excitation of the fluorescence or phosphor on the CRT due to ambient room light, the opera- tor sees a black background for the orange phosphor emission generated by the CRT electron beam. loo .o so In . _ ~ 60 a) . _ ~ 40 ~ 20 o Rejection area of blue filter =3 Rejection area of yellow-orange filter ~ ~ Area rejected by both filters \\\\\ Pass Areas gel low-Orange Fi tier \\\\ 400 500 600 Wavelength in Millimicrons Fig. 4. A diagram showing the mutually exclusive transmission curves of the room light and scope filters. These spectral transmission curves are for the cellulose acetate plastic sheet filters of the broad-band-blue system. The yellow-orange scope filter also attenuates the radiant energy of the signal and changes its color from a dichotomous blue and yellow to an orange. At first thought, it might appear that any reduction of signal intensity might degrade the performance of a scope observer, but this is not necessarily true. The performance of the human eye is determined primarily by signal-to-noise ratio (i.e., signal luminance/background luminance or "contrast ratio") and not by target energy alone. For our present purposes, background luminance is equiva- lent to photometric noise. The outcome of the changes in signal-to-noise ratio resulting from the use of the scope filter, and the specialized room illumination, may be illustrated by contrasting the broad-band-blue situation with white room light of the same intensity. Reference to Fig. 5 shows how the loss of a small amount of signal luminance, accompanied by a proportionally greater reduction in background 700 47

luminance or noise, can lead to a greatly improved ability to detect faint signals such as a trail of several seconds duration or a distant target. These illustrated improvements in the signal-to-noise ratios of a CRT reflect only the elimination of the undesirable phosphor response to ambient light. J no 0.5 c In c - . _ o 0.s - . _ a) - o 12 Ft. Lamberts of 1.2 Ft. Lamberts of White Room Light B.B. B. Room Light at 20/~ P-7 no n 0.84= Signal _ 0.5 - 1 0 - S/N ~0.74/1 P-25 10 - S/N =628/~ P-7 _ 0.54= Signal _ ~ . . . . .0086 = Noise 1 2 3 4 5 6 S/N=410/l P-25 0.34 = S ignal _ ; ~.0084 = Noise ~ 1 2 3 4 5 6 ~ 1 2 3 4 5 6 Seconds after Excitation Seconds after Excitation fig. 5. Signal-to-noise comparisons of the broad-band-blue system with white room light of the same intensity for two types of long-pers~stence phosphors. Performance characteristics required from a specialized lighting system in a radar control room Requirements vary with the equipment and function of the radar center. The diversity in function and equipment among radar centers used for air traffic control, air defense, combat control, and weather data collection is well known. Some of these differences set up different lighting requirements and others have a common solution. The range of CRT phosphors, types of judgments required of the scope observer, and whether photosensitive tools are or are not used by the radar operator determine the quality and quantity of light that can be used in the room. The location of indicators, status and plotting boards, maps, and personnel prescribes the distribution of illumination. The size' shape, and con- struction of the room, and modes of information transmission, and the amount and kind of maintenance to be carried out during operations may dictate special variations in the general solution to the lighting problem. In radar approach control centers the specialized lighting system must satisfy five major requirements. The lighting system must attempt (a) to maxi- mize GRT scope visibility, (b) to provide adequate legibility of secondary dis- plays, such as maps, flight progress strips, and status boards, (c) to provide adequate illumination for the work of supporting personnel, (d) to provide illumi- nation for training and research functions, and (e) to provide for concurrent use of other photosensitive surfaces that may be utilized in data relaying and 48

data storage. In practice each of these requirements is an aggregate, a collection of important and variously related parcels. Each requirement is discussed briefly below. We may maximize CRT scope visibility by the following procedures: (1) Elimination of phosphor excitation by the ambient illumination. If the room illumination contains radiant energy shorter in wavelength than the CRT phosphor emission, this energy will cause a general brightening of the tube face. This increase in background luminance, along with its approximation of the color of the target signal, results in an effective increase in the noise level and decrease in target visibility. It must, therefore, be eliminated. (2) Elimination of the light from the short-duration blue fluorescence of the P2, P7, and P19 classes of phosphors. Reflections of any form reduce the signal-to-noise ratio and must therefore, be minimized. (3) Provision of optimum eye sensitivity.- In the dark, the eye may become 5000 times more sensitive to light energy than it is in bright light. The advantage of utilizing some of this potential in viewing the trail of a moving target is apparent. Therefore, provision must be made for scope observers to work under dark-adaptation conditions whenever they option to do so. Many sources of information other than scope displays must be used in a control center. These include the following: (1) Permanent distal displays.- These are displays that contain relatively permanent, or infrequently changed, information. The display can be read from a distance by all personnel within the operations room. Examples include status boards, airways maps, and glide path diagrams. (2) Temporary distal displays. These are displays containing temporary, or frequently changed information. The displays must be visible from a distance and capable of being read with accuracy. Examples include hourly weather reports and facility status boards. (3) Permanent proximal dis- plays. These are those displays near the scope operator that are seldom changed. Examples include control knobs, switches, and labels showing communication channel designations, frequencies, and functions. (4) Temporary proximal dis- plays. These are displays near the radar controller that carry information of a transitory nature. Examples include flight progress strips, written messages, grease-pencil marks on the CRT, clocks, wind direction and velocity meters. General room illumination for supporting personnel should permit the free movement of personnel, the use of gestures in communicating, and the visual location of specific people and equipment. Further, it must provide for safety with enough general illumination to see obstacles, shock hazards and other sources of danger, not lead to any impairment of visual function, and preferably not create an unusual or unpleasant visual environment. The illumination system should also permit mechanical and electrical equipment to be calibrated, and minor repairs to be made, without removing the equipment from the operations room. The ambient light should permit the locating of components, the reading of printed designations, the reading of test equipment and Technical Orders, and the tracing of circuitry and reading of color codes on wires, resistors, and other components. 49

Supervisors, trainees, and visitors should be able to observe radar scopes, secondary displays, and controller activities, either with or without participation in the operations of the center. Experienced operators and supervisors must be able to give on-the-job training during normal operating conditions, including training in the use of visual displays. Testing, inspection, and research teams should be able to observe operations and gather data in the operations room without interrupting traffic control operations. Provision for concurrent use of other photo-sensitive surfaces than the human eye includes the following: ~ ~ ~ Phototubes. The option of using devices such as light guns, or light pencils, for purposes of transferring control, tracking targets, or identifying interrogating aircraft should be provided by the system. (2) Image Orthicons. Training and research agencies should have the option of using closed circuit TV in order to relay a picture of control activities to remote groups of individuals. This should, of course, be accomplished without inter- ference with normal operations. (3) Photographic materials.- The illumination system should provide the opportunity of taking still and motion pictures within the operations room without interference with the normal operations of radar air traffic control. The system should also permit the taking of frame-per-sweep photographs of the CRT, frame-per-time-exposure for long-period record keeping, and time compression motion pictures of radar tracks. In order to obtain the desired performance for detection of faint signals in noise, maximum simultaneous contrast should exist between signal and back- ground and should be maximized as to intensity and color. As pointed out earlier, it is the ratio of signal luminance to background luminance that is important here, rather than signal luminance alone. Visible phosphor persistence should not be interfered with by the visibility of the fluorescence of the CRT, the bright- ness of the sweep line, the brightness and area of video mapping, the color and brightness of proximal secondary displays, or the color and intensity of the room illumination. Phosphor persistence should have the following visible characteristics: (1) The visible positional history (trails of a moving target should be composed of three or more successive radar returns. That is, the persistence of the phosphor should be visible in excess of the time required for three antenna rotations. (2) The trail of a moving target should have the visible characteristics of decaying intensity and the related change in shape. Shape of the trail can be the major difference between correlated information from a moving target and the un- correlated visible representations of noise. ~ 3 ~ The systematic and related changes in shape' brightness differential, and separation between radar returns should be visible. These visual characteristics provide the controller with information as to identification, compliance with instructions, and the influences of external sources, such as wind, on the aircraft's track. Operational suitability tests Several tests of the suitability of the broad-band-blue lighting system have been made. A visual-skills analysis was made on eight individuals in order to determine the relative efficiency of vision under the broa~l-band-blue illumination 50

as compared with white illumination of similar brightness One set of measures was taken under fluorescent white illumination and another under the filtered blue fluorescent light. Tests were conducted on the two sources in alternation in such a way as to eliminate fatigue effects and any bias that might result from initial familiarization with one system. The Renshaw Stereodisparator and associated stereogramsr, were used for these tests. The visual measures in- cluded were: Snellen acuity for each eye alone and for both eyes at 13 in., second-degree fusion, retinal rivalry, lateral phoria, break and recovery ranges, and static stereopsis. All measures with the exception of the acuity or visual resolution tests were taken at 13 in. (near point) and at the optical equivalent of 20 It (far point). The results of these tests indicated clearly that visual per- formance is not adversely affected by the selective illumination of the broad- band-blue system as compared with white light of equal brightness. It is im- portant to note that there is no indication of any interference with accom- modation. It has been emphasized earlier that white room light interferes with scope reading by adding reflections and phosphor excitation, thus raising the intensity level of the background against which the signal is seen and effectively attenuat- ing the signal-to-noise ratio. To measure these reflectance and fluorescence effects' photometric readings were made of the background luminance of the scope face at three intensities of white diffuse light falling on the CRT. The in- strument used was the Luckiesh-Taylor Brightness Meter and the values are an average of several readings. In Fig. 6 are three solid lines representing 'noise" functions on the log-log plot. These are photometric brightness functions (com- prising diffuse reflections from the front of the CRT or filter and the phosphor- escence of the CRT) on a new P7 tube as products of the intensity of the room illumination. The upper function is for white light, the middle function for the broad-band-blue light, and the Tower function the nearest approximation for the broad-band-blue light when the operator has goggles on. This photometric bright- ness is called "photometric noise" since it is the visual background against which the controller must see the luminus intensity of the electronic signal. At the standard illumination level of 1.2 ft-l the broad-band-blue system (without goggles) has a P7 photometric noise level of 0.0086 ft-l. The noise level of white light at the same intensity is 0.70 ft-l, representing a 17.8-db increase. If the operator chooses to wear goggles the photometric noise level is less than 0.0025 ft-l or representing a 23.8-db. attenuation. The noise level with goggles is only an estimate' since 0.0025 ft-l is the lower limit of the instrument and the noise level was less than this amount. The P25 conditions are similar since white light of 1.2 ft-l produces 0.57 ft-l of noise and the broad-band-blue system pro- duces 0.0084 ft-l without goggles: an 18.3-db. attenuation. With goggles the noise level is below 0.0025 ft-l' a 23.7-db attenuation. These gains do not include any derived from increasing the sensitivity of the visual mechanism of the human observer. 5Renshaw, S. A Manual of Technical Data and Suggested Procedures for the Renshaw Visual Diagnostic and Training Split Stereograms for Use in the Stereo-Disparator. Ohio State Uni- versity, 1 948. 51

10.0 In a) 1.0 rat J to -A 0.10 a) In . _ At . _ - a) ~ 0.01 o 0.001 / / 'K' It Mean Photomet ric intensity of a 3 sec. old signal (unfiltered) ,,o~°: __~ Measureable Intensity (.0025 Ft. L.) of / was not measureable as It IS below minimum of instrument. 0.001 0.01 0.1 Room Illumination in Foot Lamberts fig. 6. "Photometric noise" as a function of white and broad-band-blue room illumination. Visual photometric noise is defined as the combined luminance from reflected light and phosphor fluorescence. 1.0 10.0 + 10.24 +0.24 -10.24 -20.24 -30.24 - to - lL - ~n a) Q . _ A critical measure of the operational suitability of the broad-band-blue system is the length of time that the persistence of the phosphor excitation from a typical radar target is visible under this and alternative systems. A prelim- inary comparison of this type has been made using simulated targets on a CRT under conditions of white room light' broad-band-blue light alone, and broad- band-blue light plus the use of goggles. The comparative results provide valuable operational suitability data, but should not be construed as representing either live radar returns or a definitive experiment. These preliminary data permit a direct comparison of the relative time the trace was visible after 5 min of adap- tation to each of the three lighting conditions. The results are given in Table 1, along with the gain ratios of the broad-band-blue system over white room light. Table 1. The Relative Time in Seconds that a Simulated Radar Return was Visible under Three Conditions of Room Illumination. Phosphor Class White light BBB light BBB light plus >-ellow-orange goggles - P19 6 84 (14:1) 217 (36:1) PI 6 66 (11:1) 132 (22:1) Note: A yellow-orange filter covered the scope for all three tests. -52

A surveys was conducted to obtain the opinions of controllers and main- tenance personnel on the operational suitability of the BBB lighting system. The opinions were asked of personnel who had worked both at Wright-Patterson Air Force Base under the BBB lighting system and in other radar locations where different illumination was utilized. Dr. Edger Chenoweth prepared an "open ended" written questionnaire containing the following questions: (1) How satisfactory is the lighting with only the blue room light and the orange scope filters? How does this system compare with the lighting in other centers you have seen? (2) How satisfactory is the complete system when the orange goggles are worn by scope observers? (3) What suggestions, if any, do you have for further improvement in the lighting system? (4) What experience have you had in radar air traffic control or in other radar operations' or in the maintenance of radar equipment? Respondents were asked to write detailed comments, and to list both favor- able and unfavorable aspects in answering the first two questions. After the first year of use of the system' the questionnaire was distributed to eleven controllers (~2 to 8 yr of experience) and nine maintenance people (1 to 8 yr experience). The most frequently mentioned favorable aspects of the BBB system were that it allowed maintenance, seeing, and moving about during RAPCON operations, it improved visibility of CRT and secondary displays, and the use of goggles added further target resolution and visibility of trail. Unfavorable comments regarding the system were that difficulty was experienced in using color coding of wires, resistors, capacitors, etc., not enough light was provided for all types of main- tenance, and goggles were uncomfortable. At the end of the third year of use the same questionnaire was distributed to ten controllers and ten maintenance people, of whom approximately 60 per cent had answered the initial questionnaire. The most noticeable result was the similarity in the proportioning of comments between the two sets of responses to Question 1 as illustrated in Table 2. . ~. ~.. . . . . . Table 2. First year (20 Respondents) Third year (20 Respondents) Favorable comments 38 (73%) 49 (73%) Unfavorable comments 14 (27%) 18 (27%) Following either one or three years use of the BBB lighting system, the opinion of operations personnel is highly similar. The comments made most fre- quently to open-ended questions are the same in each survey. These results imply that though the newness and uniqueness of the lighting installation has worn off, the opinions of operational people have remained stable and in support of the adequacy of the illumination system. updraft, C. L. A broad-band-blue lighting system for radar approach control centers: evaluations and refinements based on three years of operational use. Wright Air Development Center, 1956, Technical Report 56-71. 53

Psychologically, people prefer to work in a room illuminated with white or desaturated colored light. The BBB illumination, although distinctly colored? is less objectionable than highly saturated light. Operations and maintenance personnel who have worked in a center illuminated with the BBB system state no objection to the color of the light in the answers to questionnaires. The light contains no ultraviolet, nor does it create a problem in accommodation. The sources are cool and efficient, the filtration easy, and the cost low. The use of the short wavelengths aids in making special displays visible since these wave- lengths are capable of exciting all flourescent colors. The lighted working environ- ment is conducive to communication, industrial safety, training, inspection, and research. This illumination provides adequate visibility so that the work of sup- porting personnel can be carried on simultaneously with operations. 54

Relations Among Dark Adaptation, the Spectral Character of Illumination, ant' the Visual Task JOHN LOTT BROWN, U.S. Naval Air Development Center Summary 1. The duration and extent of dark adaptation varies with the criterion of threshold. If luminance thresholds during dark adaptation are measured for the resolution of a visual-acuity object which requires cone vision, dark adaptation is complete within 1 to 5 min. If the criterion of threshold during dark adaptation is the detection of light, or the resolution of a coarse visual-acuity test pattern, the threshold decreases during dark adaptation over a longer period of time and over a range which represents the recovery of sensitivity of rods as well as cones. 2. The visual acuity which can be achieved by the eye at a given level of illumination increases rapidly during dark adaptation and reaches a maximum determined by the level of illumination. If the level of illumination is very low, maximum acuity is delayed by the late recovery of rod sensitivity. 3. The receptors of importance in the performance of a visual task are not determined exclusively by the level of adaptation of the eye, but also by the nature of the visual task. In the com- pletely dark-adapted eye, thresholds may involve cones, rods, or a combination of cones and rods, depending upon the level of acuity which is required for the performance of the task. When a pilot must read fine markings on an illuminated instrument panel in brief glimpses, he may have to depend exclusively on cone vision. The relative effectiveness of various spectral dis- tributions of the instrument illumination would, in such cases be estimated in terms of the spectral sensitivity of the cones. 4. The cone-to-rod luminous efficiency ratio of an illuminant affords an index of the usefulness of the illuminant for the preser- vation of rod sensitivity following the performance of visual tasks which require cone vision. The advantages of the use of long wavelength distributions with high cone-to-rod ratios are evident even after exposure to adapting luminances as low as 0.1 ml. The relation of dark adaptation to the threshold criterion Dark adaptation of the eye is usually studied in terms of the decrease in threshold of the eye for detection of small spots of light in the darkened visual field after the eye has been exposed to a bright preadapting light. The exact nature of the relation between the increase in sensitivity of the eye for perform- ance of a visual task and time spent in darkness after light adaptation depends on the nature of the visual task.~~3 J' 1Brown7 J. L., Graham7 C. H.7 Leibowitz7 H.7 Ranken7 H. Luminance threshold for the resolu- tion of visual detail during dark adaptation. J. Opt. Soc. Am., 1954, 43, 197-202. Brown, J. L. Effect of different preadapting luminances on the resolution of visual detail during dark adaptation. J. Opt. Soc. Am., 1954, 44, 48-55. ~Diamond, A. L., and Gilinsky, A. S. Dark adaptation luminance thresholds for the resolution of detail following different durations of light adaptation. J. Exp. Psychol., 1955, 50, 134-143. - 55-

In Fig. 1, the curves represent decreasing luminance thresholds with in- creasing time in the dark for the recognition of a series of visual-acuity test objects as well as for the detection of light. The acuity test objects consisted of a graded series of parallel-line grating patterns which represented visual acuities of 0.042 to 1.04. It is evident that, for fine gratings, dark adaptation is a simple function which probably represents cones alone. For coarse gratings (low visual acuities), or for the detection of light, dark-adaptation curves show two branches. The higher probably represents cone function, and the lower probably rod func- tion or a combination of rod and cone function. It may be considered that specifi- cation of the time course of dark adaptation should take into account the nature of the task which the dark-adapted eye will be called upon to perform. If the task requires a level of visual acuity of 0.25 or higher, only the cone dark- adaptation process need be considered. Or the other hand, if levels of acuity below 0.25 are required, then the increasing sensitivity of rods during dark adaptation will also be of practical importance. ~ 1 0 z z ~ 0.0 J Oc~ -1 o I On LL -2.0 I ~ -3.0 o l g O VA = 1.0 4 ~ . . .. L~ A\ ~.083 \: 0.542 ~ x~ JB o \\~ ~ x SS l . . ~I 10 20 30 0 10 20 30 Tl ME IN M I NUTES Fig. 1. Luminance thresholds for different acuities during dark adaptation. The number beside each curve refers to the level of acuity. Data for subjects JB and SS. Relations between visual acuity and time-in-the-dark following light adap- tation have been derived for each of five test-object luminance levels. These relations, presented in Fig. 2, indicate a rapid increase in visual acuity for a given level of illumination during the first 5 min of dark adaptation. As level of test illumination is decreased, the initial rise in visual acuity during dark adaptation is delayed, and the maximum level of visual acuity which can be achieved is lowered. At a low level of test illumination, a delayed secondary rise in visual acuity may be found which probably represents rod functioning. At extremely low levels of illumination, only the delayed rod branch will be found. ~. . 56

-02 ~0.4 fig. 2. Visual acuity at constant grating luminance as a function of time in the dark. Curves are derived from those of Fig. 1. The number beside each curve specifies the con- stant value of grating luminance. LOG L--065 - --0.6 /// -0.8 _ / -1.0 _ 1 / I i I I 0 . 5 10 15 TIME IN THE DARK - Ml N -1 .65 1 / - -1 .8~ -2. 15 it/ - - A clearer understanding of the relative contributions of scotopic and photopic vision to the performance of visual acuity tasks by the dark-adapted eye may be obtained by examining the relation between threshold luminance and visual acuity in the dark-adapted eye. Figure 3 represents this relation for each of nine different spectral distributions of the test light.4 Luminance thres- holds were determined for the recognition of grating patterns presented in a circular 6° field, centered on the fovea. Test flashes were of 0.016-sec duration. The curves for various color filters have been shifted with respect to the curve for neutral filters in amounts indicated at the right-hand side of the figure. The results verify the conclusion which was drawn from the data presented in Fig. 1. The recognition of test objects by the dark-adapted eye can be represented by a curve which includes two branches, the higher of which probably represents cone function, and the lower of which represents rod function or the combined function of rods and cones. Cone function is required when visual acuity re- quirements are high. Only the cone branch is fourth when the test illuminant is restricted to red light. The rod branch is emphasized by the use of a deep- blue test light. Combined function of rods and cones The thresholds illustrated in Fig. 3 were measured with a variety of test-light spectral distributions for two specific reasons. First, it was hoped that possible 4Brown, J. L., Kuhns, M. P., and Adler, H. E. Relation of threshold criterion to the functional receptors of the eye. J. Opt. Soc. Am., 1957, 47, 198-204. 57

2.0 ~ 1. 1 lo Z O go -1 J ~ -2.0 o I -3. i_ -4.0 ° -5.0 -6. aft-- ~g gD.R120~) ~ o ~ -fly ~ 0+0.6 R.(~412) Y ~ ~ two 0~ ~ _~ :0.5 ~ 1 L~°? W,,-~ ~.. _ Yet ~ G.( ~ _~ , , , , ~ _, , , , , , , , -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 L OG V I SUAL A CU I T Y fig. 3. Threshold luminance as a function of visual acuity required for resolution of grating test objects. Curves have been labeled in terms of the spectrally selective filters which were used. Curves for both observers, PK and JB, have been shifted along the ordinate in amounts indicated at the right-hand side of the figure. interaction between rods and cones might be revealed by changes in the form of the rod branches of the curves with changes in the spectral distribution from shorter wavelengths to longer wavelengths. Dependence of the lower branches of the curves on rods exclusively would result in a mere shift of these lower branches with respect to the log luminance axis with changes in the color of the test flash from blue toward red, as illustrated in Fig. 4. This idea has been elab- orated in detail elsewhere. '; A single curve has been used to fit the rod branches of curates in Fig. 3. The curve is merely shifted with respect to the log luminance axis. It provides a good fit of the data of subject P.K. for all spectral distributions. However7 it is too shallow for the deep-blue test data of J.B. and too steep for the orange test light data. This would tend to indicate that some interaction be- tweer1 rods and cones may be occurring in the determination of thresholds repre- sented by the so-called roe] branches of the curves. If similar data are obtained for a 1° circular test field, the edge of which is located at a distance of 1° from the fovea, there is clearly a change in shape of the rod branches of curves with change in the spectral character of the illuminant, as illustrated in Fig. 5. Under these conditions, much of the rod branches probably represents the combined function of rods and cones. Equation of various spectral distributions for cone vision A second reason for obtaining the data which were presented in Fig. 3 was to compare the relative amounts of light, in photometric terms, which are re ''Brown, J. L., and Woodward, L. K. Rod-cone interaction in the dark-adapted eye. Optica Act., 1 957, 3, 1 08-1 14. t;Bridgman, C. S. An analysis of Taylor's data on relative luminous efficiency of various colors. J. Opt. Soc. Am., 1954, 44, 394 396. 58

quirky with different color filters for the resolution of acuity test-objects. The actual threshold luminances with the different test lights are not the same throughout the cone branches of the curves in Fig. 3. A slightly higher level of illumination is required to resolve a fine grating pattern with the deep-blue test light than is required with the neutrally filtered light, and a slightly lower level of illumination is required with the deep-red test light as compared to the 1/ Red- ~ ~J Orology,/ // ~/ Yellow ~ ///1 / / 1 Greeter /' Blue o I Ill fir I _ O _ LOG VISUAL ACUITY Fig. 4. Hypothetical curves repre- senting the completely independent function of rods and curves. 3.C L D R. (2 ~| ~ i.9 | my( o 1: ~ /: 1 ~ ~ 0.5! -1.0 -:: _ ~-0.33 I ~NEUTI ~ I ~ ~ ~ .2 | --3.0 - r ~ ~/ O / ~ J ~_/ _ / V.A.e 203 .290 .490 D. B. ~.203 .290 .490 .054 .105 .168 .246 .417 ~ .IOS .168 .246 .417 -5.0 ~ 1 · 1 . ~ 1. 54 , ~ - 1. 30 - .80 -.30 - 1 .30 - .80 -. 30 LOG V I SUA L AC U ITY Fig. 5. The relation between threshold luminance and visual acuity for stimulus conditions slightly different from those illustrated by Fig. 3. -59

neutrally filtered light. The data of Fig. 3 thus afford a basis for adjusting adapting lights in accordance with the actual luminance requirements for per- formance of visual tasks which depend on cone vision. Dark adaptation following spectrally selective light adaptation The same two subjects were adapted to each of four levels of illumination with each of the spectral distributions represented in Fig. 3. Adjustments in the levels of adaptation were made in accordance with the positions of the cone branches of the curves for the different color filters in Fig. 3. Adaptation levels were approximately 10O7 10, 17 and 0.1 ml. Subjects were dark adapted prior to light adaptation at these levels and light adaptation was of 5 min duration. A circular area' 35° in diameter' which was centered at a distance of 10° from the fovea on the temporal side of the retina, was used as the light-adapting field. Fol- lowing light adaptation, dark adaptation was measured with a 1° circular test area illuminated with "white" light which was presented in 0.016-sec test flashes in the center of the light-adapted area. Dark-adaptation measurements were continued until there was little further drop in threshold with repeated presentation of the test flashes. Threshold measurements were continued out to nearly 30 min of dark adaptation following light adaptation at the two higher luminances. These data afford some interesting comparisons of the effect of a variety of spectral distributions of the adapting light on the sensitivity of the eye. Before presenting the results of the dark-adaptation experiment, however' it is of interest to review some of the theoretical bases for the advantage of long- wa~relength illumination over illumination of shorter wavelengths. The cone-to-rod luminous efficiency ratio In Fig. 6, the luminous efficiencies of both rods and cones are presented along with two distributions of radiant flux.7 One of these distributions is an equal energy spectrum, and the other represents a red light which includes little or no energy below 600 me in wavelength. Theoretically, these two radiant flux distributions are equally exciting to the cones. This is illustrated by multiplying the radiant flux in watts by the photopic luminous efficiency in lumens per watt over the visible spectrum. The results of these calculations are represented graphically in Fig. 7 by the solid curves. The sharp' peaked curve centered at 650 me represents the red illuminant, corrected for cone sensitivity. The shorter' broader curve centered at 550 my represents the equal-energy source, corrected for cone sensitivity. The areas under these two curves are the same, and it may therefore be assumed that they are equally effective in stimulating the corles. The products of the same two energy distributions multiplied by the scotopic or rod luminous efficiency are represented by the dashed lines in Fig. 6. It is clearly evident that the area under the corrected curve for the equal-energy source is much greater than the area under the corrected curve for the red-light source. It may, therefore be concluded that although the red-light source and ~Brown, J. L. Review of the cone-to-rod ratio as a specification of lighting systems. Illum. Eng. 1946, 51, 577-584. 60

equal-energy source are equally effective for performing tasks with cone vision, the equal-energy source will be.much more damaging to rod sensitivity than will the red source. These calculations afford a possible basis for the specification of any spectral distribution in terms of its effect on dark adaptation after exposure to levels of illumination appropriate for the performance of some task which depends on cone vision. The equal-energy distribution provides a convenient reference. When a given spectral illuminant is equated with an equal-energy source for ~ 1200 In Z 1000 :, z lo ~ 400 800 600 g 200 o rS COTO PI C L U M I NO U S / E FF IC I E N CY /\ / DISTRIBUTION R- /\ / RADIANT FLUX -\ PHOTOPIC / ~// OF RED FILTER - \ LUMINOUS / ~ ~TUNGSTEN SOURCE CIENCY/ ~ / COMBINATION V / i /\ / \ \ | DISTRIBUTION E | RADIANT FLUX OF EQUAL ENERGY |\~SOURCE 350 450 550 650 750 WAVELENGTH-MILLIMICRONS to 11 D 40 D Z 30 r x 20 1 D 10 (in _ O Fig. 6. Photopic and scotopic luminous efficiency curves, and radiant flux, as a function of wavelength for two hypothetical sources. 600C At ~ 5000 J ' 4000 x . J LL 3000 ° 200C J IOOC / SCOTOPIC LUMINOUS \ FLUX OF EQUAL \ ENERGY SOURCE \ / ~PHOTOPI C \ ~\ rLUMI NOUS \, \ I FLUX OF Y \ ~ EQUAL `` ~ E N E R GY I SO U RCE / it / ~\\~ 350 450 550 650 750 WAVELENGTH - MILLIMICRONS - PHOTOP I C LUM I NO US FLUX OF RED LIGHT -- S C OTOPI C · UM I NOU S FLUX OF RED LIGHT Fig. 7. Luminous flux as calculated for each of the four possible combinations in Fig. 6.

cone vision, the relative excitation of the rods by this illuminant, as compared with the excitation of the rods by the equal-energy source, may be expressed as a ratio. The ratio may be calculated by dividing the scotopic luminous flux of the illuminant into the scotopic luminous flux of the equal-energy source. This ratio represents the relative stimulating effect of the illuminant on cones as compared with rods.7 This kind of a ratio is termed a cone-to-ro~ luminous off iciency ratio. Dark adaptation as a function of the cone-rod ratio of the adapting light Results of our dark adaptation experiment are presented as a function of cone-rod ratio of the adapting light in Fig. 8. The four curves for each subject represent thresholds after 1 sec of dark adaptation for each of the four levels of light adaptation. It is evident that7 at each of the four levels of light adaptation, an increase in the cone-to-rod ratio of the adapting light results in a decrease in the logarithm of threshold luminance for light detection after 1 see of dark adapta- tion. This decrease appears to be just as great after light adaptation to 0.1 ml as it is following light adaptation to 100 ml. The results are quite similar for the two observers and clearly illustrate the advantages afforded by red illumination in situations where it is important to maintain a high level of sensitivity of the eye for rod vision. THRESHOLD AFTER I SECOND DARK ADAPT AT ION 0.0E to 0 - 2.0 an I )-3o -I o ~ ooF JR PK L i 9 ht Ada ptat i of Lum i nance 0 0 = 2.0 Log ML x x = 1.0 '' .' ·- =0.0 .' '' =-1.0 , , , . , . , . , . , . 1 - 1.0 o.o 1.0 -1.0 o.o 1.0 LOG CONE-ROD RATIO Of ADAPTING LIGHT Fig. 8. Threshold luminances after on.e-sec dark adaptation as a function of the cone-to-rod ratio of the adapting light. Subjects JB and PK. Figure 9 is similar to Fig. 8 but represents the logarithm of mean threshold luminance for light detection after 20 sec of dark adaptation. There is an - ~Brown, J. L. Beview of the cone-to-rod ratio as a specification of lighting systems. Illum. Eng. 1946, 51, 577-584. 62

~ -1 .0 an J c' -2.0 J I lo ~ -3.0 o J \ ~ '\ \ \~ JB \ 0 of xx \ -10 0.0 1 0 -1.0 -2.0 -3.0 P K A oo = 2.0 _ x x = 1 .0 ·e = 0.0 ~ ~ = 1.0 1 , -10 0.0 10 Log It 11 11 1 ML 11 11 - LOG CONE-ROD RATIO OF ADAPTING LIGHT Fig. 9. Mean threshold luminances after 20-see dark adaptation as a function of the cone-to-rod ratio of the adapting light. Subjects JB and PK. interesting change in the shape of the curves as compared with Fig. 8. Straight lines no longer seem to afford an adequate fit, and, at the lowest level of light adaptation, the data appear to require a curve of two branches. As in the case of the 1-see dark-adaptation threshold, the advantage of a high cone-to-rod ratio is found to hold up, even following the lowest level of light adaptation. Following light adaptation to a luminance of 0.1 ml, the light detection threshold for a "white" test light is 10 times higher when the adapting light is deep blue than when the adapting light is a deep red. The situation at still later times during dark adaptation is illustrated in Fig. 10. The curves in the upper part of the figure represent mean thresholds measured after 1 to 2 min of dark adaptation. Although somewhat more com- pressed, the curves are very similar to those presented in Fig. 9. Thresholds after 5 to 6 min of dark adaptation are presented in the lower portion of Fig. 10. After this interval of dark adaptation, the early advantages gained by the use of a red adapting light have nearly disappeared at the lowest light-adaptation luminance. The disadvantage of deep-blue light adaptation, however, is still clearly evident following adaptation to a luminance of 10 ml. Data presented in Figs. 8, 9, and 10 represent a limiting condition: the nature of dark adaptation, as measured by a rod threshold, following levels of light-adapting illumination which have been equated in terms of cone function. Under these conditions, there is a clear advantage to be gained by the use of illuminants which are restricted to the longer wavelengths. As we have illustrated, visual tasks which require a low order of visual acuity may depend on the com- bined function of rods and cones. The advantages of using a high cone-to-rod ratio illuminan.t may be somewhat reduced when dark adaptation is considered in terms of a visual task to which the cones contribute. 63

MEAN THRESHOLD AFTER I TO 2 MINUTES DARK ADAPTA T I ON -1.0 JB PK Light Adoptation \ -1.0 - Luminonce \ \,, ° 0 = 2.0 Log ML W - 2 . 0 ~ \ ~ -2.0 hi) -3. 0 _ -3.0 _ 1 , I , I ~ -1 0 0.0 1.0 -1 0 0.0 1.0 MEAN THRESHOLD AFTER 5 TO 6 MINUTES DARK ADAPTATI ON -2. O _ -~ ` -3.0 _~ . --10 0.0 1.0 -10 0.0 1.0 LOG GONE-ROD RATIO OF ADAPTING L I G HT Fig. 10. Mean threshold luminances after 1 to 2 min and after 5 to 6 min dark adaptation as a function of the cone-to-rod ratio of the adapting light. Subjects JB and PK. 64

Effects of Certain Pre-Exposure Variables on Dark Aciaplation* JOHN A. HANSON, Tufts University Summary Three experiments demonstrated effects of pre- exposure on subsequent dark adaptation. A modified Crozier- Holway discriminometer was used to measure pre-exposure tolerance of the peripheral retina, effect of pre-exposure size on foveal dark adaptation, and its effect on peripheral dark adapta- tion. Results indicate that exposure for 100 ft-1-seci or less im- pairs peripheral, but not foveal, sensitivity. This paper presents the findings of three recent investigations of the "white" light pre-exposure tolerance of the dark-adapted and partially dark-adapted human eye. These studies were conducted in an attempt to arrive at a com- promise solution to the conflicting illumination requirements inherent in operational situations in which it is necessary for an individual to perform tasks requiring good visual acuity and also to identify targets under low levels of illumination. The main problem is to determine whether or not the dark-adapted eye can be exposed to light of sufficient luminance and duration for the performance of many acuity tasks and at the same time suffer only minimal loss of sensitivity. Emphasis has been placed upon the preservation of foveal sensitivity rather than peripheral rod sensitivity with the belief that, in the modern operational situa- tion, low brightness tasks involve form identification more than detection. Previous studies.in this series investigated the effects of pre-exposures of various brightnesses and durations on foveal sensitivity. The major finding was that foveal dark adaptation is too slight to be measured by the techniques used, following pre-exposures of the dark-adapted eye to light in which the luminance-duration product is 100 ft-1-sec, or less. This finding suggests that maximum foveal sensitivity may be maintained during tasks requiring high visual acuity if the luminance-duration of the illumination is controlled below 100 ft-1-sec. Pre-exposure tolerance of peripheral retina The three studies to be reported in this paper are extensions of the earlier studies. The first study reported here investigates the pre-exposure tolerance of the dark-adapted peripheral retina in order to answer two questions: (1) What effect does pre-exposures of 100 ft-1-sec have on the sensitivity of the dark-adapted peripheral retina? (2) Assuming that an exposure of 100 ft-1-sec causes an ap- preciable rise in peripheral thresholds, are there pre-exposure combinations of practical magnitude which would result in little or no decrement in peripheral *This work- was supported by Office of Naval Research Contract l\ionr-494(12) Footlambert-second is represented by f t-Z-sec. 65

sensitivity? Although the main purpose of the experiment was to determine the pre-exposure tolerance of the peripheral retina, a limited number of pre-exposure luminances and durations were used to retest the fovea so that the present ex- periment would have some common conditions for comparison with the previous studies. A modified Crozier-Holway discriminometer was used. The instrument consists of two main paths which can be individually controlled with respect to size, brightness, position, and duration of exposure. A third auxiliary path is used to provide fixation points. The pre-exposures are presented by means of one main path, the test flashes by the other. The eye tube enters a light-tight booth where the observer sits. A head holder fixes the observer's eye in position relative to the eyepiece of the instrument. The optical arrangement provides a Maxwel- lian view of both the pre-exposure field and the test patch. For calibration of luminance, three observers made binocular matches in which one eye viewed a field presented by the discriminometer and the other eye viewed a field of similar size and known luminance through an artificial pupil. The luminances presented to the eye by the discriminometer in this ex- periment are equivalent to luminances of a diffusing surface viewed with a pupil size of 3. 77-mm diameter. In the main part of the experiment, the testing of peripheral locations, fixa- tion was provided by a red spot approximately 20 min of arc in diameter. For foveal threshold determinations, fixation was provided by four blue dots posi- tioned at the extremities of an imaginary, vertical cross. When the observer fixated the intersection of the imaginary cross lines, the four dots were positioned 3° above and below, and 3° to the right and left, of the central fovea. The test patch was a square, 1° on a side, which was presented for a duration of 0.033 sec. The pre-exposure field was circular, measuring approximately 55° in diameter. Under all conditions, fixation of the field was central; fixation was provided by ~ ~ ~ ~ · . . ~ ~ 1 ~ . _ _ cllagona1 cross-hairs. l Free peripheral locations were tester. 1 ne locations, measured from the central fovea, were 2°, 6°, and 18° on the horizontal temporal . ~ . meridian. There were two observers, both females in their mid-twenties. Before pre- exposure, the observers adapted to darkness. When foval thresholds were to be determined, adaptation lasted 10 mini when peripheral thresholds were to be determined, adaptation lasted 30 min. Pre-exposure luminances investigated there 0.01, 0.1, 1., and 10 ft-l for durations of 1 and 10 sec. Therefore, the range of luminance-duration products was 0.01 to 100 ft-l-sec. Peripheral locations were tested with all combinations of pre-exposure luminance and duration. The fovea, however, was tested only following pre-exposures of 10 ft-l for 1 and 10 see and of 1 ft-l for 10 sec. Absolute thresholds were determined using a modified method of limits in- volving the ascending series only. The first transtional judgment was accepted as the threshold. One dark-adaptation curve was obtained following each pre- exposure condition for each observer. 66-

The results of the retest of the fovea were in slight disagreement with the results of the previous study. There appeared to be a measurable loss of sensitivity following the pre-exposure of 100 ft-l-sec. Whether adaptation is demonstrated following the two pre-exposure combinations yielding 10 ft-l-sec is impossible to state positively, in view of inherent variability in threshold determinations. However, slight adaptation appears to have taken place in at least one of the conditions ( 1 ft-l for 10 see). In general, the following results were similar at all three peripheral loca- tions tested: ( 1 ~ The three pre-exposure combinations of greatest magnitude re- sulted in a substantially greater sensitivity loss than the remaining combina- tions. (2) Reciprocity of luminance and duration appeared to hold for all three reciprocal relations tested. At 2°, all conditions resulted in a measurable sensitivity loss. However, the effects of pre-exposure combinations of 1, 0.1, and 0.01 ft-l-sec were not appre- ciably different. At both 6° and 18°, pre-exposure combinations of 0.1 and 0.01 ft-l-sec produced little or no loss of dark adaptation that could be measured by the technique used. Effect of pre-exposure size on foveal dark adaptation The same apparatus was used as in the previous experiment, with the follow- ing modifications: (1) A 10x wide-field eyepiece replaced the previously used 20x wide-field eyepiece in order to increase the maximum obtainable brightness. This reduced the maximum subtense of the pre-exposure field from 55° to 37 5°, however. (2) The conventional slit mechanisms in both pre-exposure and test- patch paths were replaced by ones which provided circular apertures. (3) The previously used blue fixation points were replaced by red ones (in the same orientation) in order to make the fixation points visible after the higher pre- exposures. A check comparison indicated no differences between dark-adaptation curves as a function of the color of the fixation points. The pre-exposure sizes investigated were centrally-fixated circular fields with diameters subtending 1°, 2.5°, 5°, 10°, and 37.5°. Each size was presented at the to~ow~ng ~um~nance-oura~on combinations: 1 ft-l for 10 see; 10 ft-l for 10 see; and 1000 ft-l for 100 sec. Thresholds were obtained using the same tech- niques as in the previous studies except that the test patch was a 1° circle rather than a 1° square. .~ r ~ ~ ~ ~ ·~ Two observers, a female (EA) and a male (RW), both in their late twenties, served in the experiment. Three curves were obtained, and average curves were computed for each observer under each condition. The average curves were com- puted as follows: The obtained threshold points of each of the three curves were drawn perpendicular to the abscissa at regular time intervals. The points of intersection of the three curves on each perpendicular were read off the ordinate and averaged. In Fig. 1, the average points are enveloped by line segments connecting the highest and lowest intercepts on each perpendicular. The effects of increasing 67

BRIGHTNEss SIZE- lo 2.S° DURATION I FT-L 10 SEC. 21 ~2 5° 10° 37 5° 2L .~2: lO FT-L 8 IO5EC. I I I 24___ 2: _2~ 2~__2_ a' -- 2 jet 22 24 air: 0 100 200 400 600 0 100 200 600 0 100 200 400 600 o 100 200 400 600 0 100 200 400 600 TIME -SECONDS Fig. 1. Average foveal dark adaptation curves for two observers (filled circles - RW; open circles - EA) following various sizes of pre-exposure field presented at three luminance-duration combinations. pre-exposure size for a given luminance and duration of pre-exposure are shown by the five curves that appear side by side in a given row. In general, there appear to be no differences in the curves as a function of pre-exposure size for any of the luminance-duration combinations employed except after 1000 ft-l for 100 see with a 1° pre-exposure field. This curve shows a lower initial threshold and reaches a final threshold earlier than the other curves of the row. This may be a real effect, or it may be an artifact resulting from the inherent difficulty in reliably testing a small retinal area with a test patch the same size as the pre- exposure field. Imperfect fixation could result in both incomplete pre-exposure of the retinal area to be tested and inadvertent testing of unexposed retina. To test the hypothesis that imperfect fixation could be a factor, a 1/3° test patch was used to compare the effects of 1° and 37.5 ° pre-exposure fields at 1000 ft-l for 100 sec. The results were inconclusive since both observers showed some size effect, although the magnitude of the effect was markedly reduced. Effect of pre-exposure size on peripheral dark adaptation The apparatus used in this experiment was the same as in the previous experiment except that fixation was provided by a single red fixation point. Three peripheral locations were tested: 2°, GO, and 15° on the horizontal tem- poral meridian of the right eye. A preliminary experiment, using a wide range of centrally fixated pre-exposure sizes, had indicated no differential effect of pre-exposure size when the pre-exposed area did not include the area being tested. Therefore, in order to concentrate the data, three pre-exposure sizes were chosen to test each peripheral location. These sizes were such that the small size would not pre-expose the area to be tested, the intermediate size just included the area to be tested, and the large size was as large as the apparatus would per- mit. The sizes used to pre-e~`pose each location were: 1°, 5°, and 37.5° at the 2° 68

location; 2.5 °' 15°' and 37.5° at the 6° location; and 5°, 32°, and 37.5 ° at the 15° location. Two pre-exposure luminance-duration combinations were used: 0.1 ft-l for 10 see, and 10 ft-l for 10 sec. Three dark-adaptation curves were ob- tained for each condition by the same observers as in the previous experiment. The results are shown in Figs. 2 and 3. Average points and ranges are shown as before. All pre-exposure conditions resulted in some loss of subsequent sen- sitivity. For all sizes and locations' the greater luminance during pre-exposure resulted in more loss of sensitivity. For those sizes which did not stimulate the tested area, this effect may have been due to the increased amount of stray light in the instrument and eye. RE~NAL LOCATION TESTED 2° 6 tn 3 he or m 15° SIZE 2 t . .~ ..°.: ~ ~ ~ SMALL INTERMEDIATE LARGE 2t 3 E. . . ~ 3- . con- 3 4' , ,, ,, , 1 ~ , . . ,, , I , i.t,l.' . ~ ~ l 1 l 1 ~ 111 I'DI: 4~' 11.11 , ~ I ~ I ~ I I'1'1~ I ~ I I ~ ~ islet- · ~ ~ ·~ ~ I ~ ~ In 1 . ~ 34= 4 o loo 200- 400 600o 100 200 400 600 TIME-SECONDS 2- . . ~ . 3 .' . O. j Q..,'t. ~ .~,,,..~ ' - ` ~ 2 ~ ~ Fig. 2. Thresholds at three peripheral locations for two observers {filled circles - RW; open circles - EA) following presentation of three sizes of pre-exposure field at a luminance of 0.1 ft-l for 10 sec. For all locations, the pre-exposure sizes that stimulated the area to be tested had a much greater effect on dark adaptation than those which did not stimulate this area. The sensitivity loss following the intermediate pre-exposure size was as Great as the sensitivity loss following the large pre-exposure size. The sensitivity loss at the 15° location, following the intermediate- and large-size pre-exposures, was greater than the loss at 2° and 6° locations. How- ever~ the overall effects of size were similar at all retinal locations tested. The results of these three experiments, together with the results of the previous studies, indicate that maintaining foveal sensitivity with "white" illumi- nation is probably feasible. Adaptation appears to be only slightly affected 69

RETINAL LOCATION TESTED 2 2° 3 l 4L 6° ~_ o 1 an an At, he - following ~easonably adequate luminances and durations of large pre-exposure fields. The maintenance of peripheral sensitivity, however does appear not to be feasible. An investigation is now being made to determine the length of dark period necessary between pre-exposures to avoid the accumulation of effects during long series of pre-exposures. This investigation will be followed by a wavelength study on the effects of various narrow-band pre-exposures on thresholds for colored test patches. Assuming that these studies enable us adequately to specify an illumination system capable of preserving foveal sensitivity' it seems de- sirable next to determine the visual tasks to which the system applies. Sl Z E SMALL W...°:~-.-. 2-1 1 ~ I l 1 ~ 1lil1 , ~ I, 1 ~ - 4 2 3 '`.,°,,,0 on' 4-: 1 l 1 ~ 16111 :~° 4 . INTERMEDIATE LARGE i_ ~ · ~ l i ' I ' I 'I'm I :,~Do ., ~ o ~ . ~ · ~ '1 ' 1 l 1 ~ 111 . . l ~ ~ 1 ~l 1 ~ 1'1'1 1,,,, 1 1 1 1 l ill _ _ . 2- 2 5° 3 3 4'~- 4 o 100 200 400 600 ~_` 3 .° o -- 4 t: [A 4~ ~- ..... . . . . . .. . . . . . , , . . . . . . o 100 200 400 600 o 100 200 40~0 600 TIME-SECONDS Fig. 3. Thresholds at three peripheral locations for two observers (filled circles - RW; open circles - EA) following presentation of three sizes of pre-exposure field at a luminance of 10 ft-l for 10 sec. -70

Making Raciar Inclicators Useful in High Ambient ItIumination J. R. ROEDER, Westinghouse Electric Corporation Summary The design of the electrical portion of the indicator must take into account pulse width, pulse repetition frequency, sweep speed of the indicator, antenna scanning pattern, and video amplifier bandwidth. The characteristics of the converter must be considered in selecting the picture tube and the phosphor in the picture tube. The design of the optical portion of the indicator must take into consideration the geometry of the specific installa- tion. Hood design cannot be divorced from geometry, and the magnitude of the reflection problem is determined by the geom- etry. The best present-day indicating system for fighter aircraft consists of a bright tube, a circular-polarizer filter with a non- reflecting first surface, and a sun shield. The radars of fighter aircraft are excellent today, with the indicating system probably the weakest link in the chain for the single-place aircraft. In a one-man aircraft when the pilot must look at the sun, clouds, and sunlight on his instrument panel, it is very difficult for him to look also at the picture tube of his radar indicator and see small, weak targets. The smaller and weaker a target the pilot can see, the greater is the detection range of the radar. Every mile that can be added to the range of a fighter aircraft radar is of great im- portance because of the supersonic speeds at which aircraft can fly. Obviously, the higher the speed of approaching aircraft, the less is the time available for maneuvering and for preparing to fire. Every second gained is important. High- speed aircraft, approaching each other at several times the speed of sound, do not have enough seconds to get ready to fire missiles. The pilot must see the target before the weapon system is of any value. In the 20-year development of radar, a great many improvements have been made. The signal-to-noise ratio has been improved, the noise of the first amplifier tubes has been reduced, improvements have been made in crystal noise, etc. A great deal can be found in the literature about these subjects, but prac- tically nothing can be found on the use of indicators under high ambient light conditions. It has been only recently that the operation of radar under high ambient light has been extensively studied. Therefore, it is the author's opinion that there is more to be gained at this time towards improving detection range by expending engineering effort on the indicating system than on any other portion of a radar. Detection range must be increased to make fighter radars more useful. Electrical inputs to the indicating system are shown in Fig. 1. The video signal input has noise plus pulses with the intelligence. The characteristics of the pulses are: (1) pulse width (parsec), (2) pulse repetition frequency (prf), and (3) sequence repetition, determined by antenna pattern. The output is optical. The hood is used to keep direct sunlight off the face of the picture tube. The optical output must be bright enough so that the pilot can see it in the presence of -71

bright sunlight. At high altitude, most of the light appears to come up into the pilot's eyes, being reflected off clouds. SUNLIGHT FIRE CONTROL RADAR I NDICATOR E LECTRI CAL OPTI CAL I N PUT O UTPUT 7 HOOD in / ~ / PILOT'S / EYE SUNLIGHT REFLECTED OFF CLOUDS Vl DEO SIGNAL Fig. 1. Fighter-aircraft radar indicator blocic-diagram. To obtain the best detection range with the electrical inputs, we must get as much light output as possible. One thing that must be done is to make the range- sweep speed compatible with the minimum scot-size of the picture tube. The slowest range-sweep in Fig. 2 takes about four times as long as the pulse width to cross the minimum spot-size on the picture-tube phosphor. This means that the electrical signal causing the light output of this spot is the average of the target pulse and the noise. The apparent target intensity is as shown at the bottom of Fig. 2. As the range-sweep is made faster, the time required to generate the minimum spot-size is about twice the target pulse time. Hence, the average of the target pulse and noise gives a larger apparent target intensity than for the slower sweep. The next sweep shown crosses the minimum picture-tube spot-size in a time equal to the target pulse width. At this sweep speeds the optimum ONE MILLIMETER DEFLECTION I N t 6 MILLIMETERS | 4 2 APPARENT ~ , TARGET I NTENSITY . _ _ M I N I MU M SPOT SIZE ~TIME(microseconds) ,L] ~11-RADAR SIGNAL Fig. 2. Detection is improved when sweep speed is optimized for pulse width and minimum spot size. 72

apparent target intensity is achieved. Making the sweep faster, as shown, will obviously make the target larger but will not make the target more intense per unit area. In order not to deteriorate detection range, the indicator must have a sweep speed greater than that determined by the minimum spot-size of the picture tube. In actual equipment for the case of a 50-mi range sweep, a 10 per cent increase in detection range was calculated. Actual flight test data indicated better detection range for a very small target on a 12-mi range than on a 24-mi range, thus verifying the calculations. The effect of picture-tube phosphor characteristics on light output is shown in Fig. 3. The pulse width and the time between pulses affect the light output. These parameters are often determined by other requirements of the radar, but information about the relationship of these parameters to the light output and what the pilot can see can be used to improve detection range. Conventional picture tubes do not store information long enough to make the antenna pattern of any importance. However, with the storage tube there is a buildup of light output by additional passes of the antenna across the target. The insert in Fig. 3 shows the relative light buildup for a conventional picture tube with P2 and PI phosphors under pulsed operation which is typical of radar indicators. This shows how important the selection of the phosphor is to obtain the most light output. The time between target pulses is typically 1,000 times as long as the target pulse. The greater the duty cycle or ratio of pulse time to off time, the better is the detection range. mono 900 800 ~ 700 ~n At 600 by 500 400 - / 300 1 \1 / / / / ,, ~ Ah\ ~ ~ ~ P2 TIME- ~ Vl DEW Fig. 3. Pulse width and time between pulses determines brightness of picture tube. The transfer function of voltage input to light output for a conventional picture tube is shown in Fig. 4. Target signals of three different amplitudes are shown with idealized noise signals. To improve detection range, the small target signals are the ones to study. The amount of light visible to the pilot's eye will change with the ambient illumination. Hence it follows that the electrical signal required to produce this light will vary with the ambient light. It is also inter 73

esting to note that the gain of the conversion of the electrical signal to light is not constant because of the changing slope of the curve. There is better gain at high- intensity light output. LOGA R ~ TH M I 1 1 VOLTAGE FOR / I ZERO LIGHT OUTP;/ I ~- - ~ ELECTRICAL SIGNAL (volts ) == , - o - z w I J Fig. 4. Transfer function (volts to light). Thus far we have considered electrical-output signal characteristics, as well as how variation of the component parts of the signal affect detection range. The transfer characteristics of the picture tube (the electrical to optical converter) have also been shown. This leaves the strictly optical portion to be considered. Reflections are a big problem. When enough target light is available, a circular-polarizer filter has been found to improve greatly the usefulness of the indicator. Test pilots report very favorably on circular-polarizer filters when used with bright tubes. The light from the pilot's bright-orange life vest, his white, shiny helmet, and other bright spots pass through a linear polarizer. It is then rotated 45°. If it should be reflected from any one of a number of surfaces, it makes no differ- ence, since it is rotated another 45° on its return trip. It is now rotated 90° with respect to the linear polarizer and' hence, is greatly attenuated as it passes through on its return trip. It should be noted that, with conventional picture tubes, the 60 per cent one-way loss of light cannot be tolerated, but with the brighter picture tube, the circular polarizer appears to give a very great improvement. The 74

circular polarizer reduces all rear-surface reflections. If a nonreflective coating is added to the first surface, we have improved our equipment greatly as far as reflections are concerned. If light could be eliminated from the face of the indicator, we would not have a reflection problem. Many types of hoods have been built, but as each hood must be designed for a particular installation, it becomes a problem in geometry. The installation of the radar indicator in fighter-aircraft cockpits is very important. From all the work Westinghouse and others have done, both in development and on specific problems, it is felt that the best state-of-the-art fighter-aircraft indicating system consists of a bright tube, a circular Polaroid filter with a non- reflective coating on the first surface, and a simple sun shield, as shown in Fig. 5. The bright tube is used to overcome the high-ambient-light problem. The cir- cularly polarizing filter is used to eliminate all multiple rear-surface reflection. The nonreflective coating on the first surface is used to eliminate first-surface reflections, and the indicator has a simple sun shield to keep off direct sunlight. Over a dozen flight tests with the bright-tube indicator have yielded excellent results in comparison with existing equipment. With direct sunlight on the in- dicator at 30,000-ft altitude, targets are visible, but further improvement ap- pears possible. BRIGHT TUBE I NDICaTOR - l SIMPLE SUN SHIELD 'en\ C IRCULAR NON-REFLECTIVE POLAROID SURFACE FILTER Fig. 5. Best indicating system flight tested. 75

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