Illumination and Visibility of Radar and Sonar Displays Proceedings of a Symposium (1958) / Chapter Skim
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Session II - Methods for Controlling Ambient Illumination
Session II - Methods for Controlling Ambient Illumination
Pages 33-76
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From page 33... ...
S Navy Electronics Laboratory SOME APPLICATIONS OF CONTROLLED WHITE LIGHTING Fred G
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Emphasis is placed on the use of white light. Polarized white light is specially advantageous for the illumination of cathode-ray tubes.
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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 illuminant at all if it is found that it is operationally better to have a particular display in relative darkness.
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From page 36... ...
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)
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~ 3 ~ Whenever possible, white light should be used. Full spectrum illumination best meets the needs for most work positions, including those with CRT displays.
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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.
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From page 39... ...
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.
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From page 40... ...
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.
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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.
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2. Elements of light control at radar console: {A)
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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.
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From page 44... ...
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.
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From page 45... ...
end of the visible spectrum is somewhat 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.
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From page 46... ...
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)
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From page 47... ...
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.
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From page 48... ...
to maximize GRT scope visibility, (b) to provide adequate legibility of secondary displays, such as maps, flight progress strips, and status boards, (c)
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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.
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(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.
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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.
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Phosphor Class White light BBB light BBB light plus >-ellow-orange goggles P19 6 84 (14:1)
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(4) What experience have you had in radar air traffic control or in other radar operations' or in the maintenance of radar equipment?
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This illumination provides adequate visibility so that the work of supporting personnel can be carried on simultaneously with operations.
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4. The cone-to-rod luminous efficiency ratio of an illuminant affords an index of the usefulness of the illuminant for the preservation of rod sensitivity following the performance of visual tasks which require cone vision.
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Relations between visual acuity and time-in-the-dark following light adaptation have been derived for each of five test-object luminance levels. These relations, presented in Fig.
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Cone function is required when visual acuity requirements are high. Only the cone branch is fourth when the test illuminant is restricted to red light.
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3. Threshold luminance as a function of visual acuity required for resolution of grating test objects.
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From page 59... ...
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.
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From page 60... ...
3 thus afford a basis for adjusting adapting lights in accordance with the actual luminance requirements for performance 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.
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6. Photopic and scotopic luminous efficiency curves, and radiant flux, as a function of wavelength for two hypothetical sources.
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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 adaptation. This decrease appears to be just as great after light adaptation to 0.1 ml as it is following light adaptation to 100 ml.
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From page 63... ...
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.
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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.
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From page 65... ...
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.
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From page 66... ...
In the main part of the experiment, the testing of peripheral locations, fixation was provided by a red spot approximately 20 min of arc in diameter. For foveal threshold determinations, fixation was provided by four blue dots positioned at the extremities of an imaginary, vertical cross.
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From page 67... ...
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)
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From page 68... ...
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 temporal meridian of the right eye.
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From page 69... ...
2. Thresholds at three peripheral locations for two observers {filled circles - RW; open circles - EA)
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Assuming that these studies enable us adequately to specify an illumination system capable of preserving foveal sensitivity' it seems desirable next to determine the visual tasks to which the system applies.
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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.
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From page 72... ...
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 rangesweep speed compatible with the minimum scot-size of the picture tube.
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From page 73... ...
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.
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From page 74... ...
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.
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From page 75... ...
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 nonreflective coating on the first surface, and a simple sun shield, as shown in Fig.
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