Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson (1968) / Chapter Skim
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FLASH BLINDNESS
FLASH BLINDNESS
Pages 85-144
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From page 85... ...
The specific devices which have been developed and which are being evaluated at this time, are discussed elsewhere in this Report. In considering the effects on vision of the light from a nuclear burst, there are, in fact, two major areas of concern: one deals with the permanent damage, or retinal burns, and the other with temporary impairment, or flash blindness.
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From page 86... ...
Thus, if any features within the cockpit can be arranged to provide benefit, such as an automatic increase in cockpit lighting following exposure, the period of flash blindness can be decreased, even though the overstimulation of retinal chemicals has in no way been changed. Such a concept is important since it allows one to consider means of reducing flash blindness above and beyond the obvious one of providing direct protection for the eye.
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From page 87... ...
2. a pilot from flash blindness at much greater distances from the burst than is required for protection from thermal radiation effects on his skin.
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From page 88... ...
Here, again, any light which produces flash blindness or even destroys dark adaptation could be quite serious. Many persons have proclaimed that with airborne radar and 88
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From page 89... ...
Realizing the importance of maintaining the visual capability of Navy personnel under combat conditions, the Navy has had, for several years, an active program to investigate flash blindness and to develop protective devices and procedures.
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From page 90... ...
5. example, that a period of flash blindness that would last from 20 to 30 sec under normal lighting can be reduced to approximately 2 sec simply by floodlighting the visual task with 50 foot-candles.
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From page 91... ...
Useful vision is regained in the protected eye almost immediately following the flash, while vision through the exposed eye may remain impaired for many seconds. The major problem with this protective device, however, is that since vision is so critical to most missions the maintenance of vision in one eye is generally regarded as only a poor interim solution to the protection problem.
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From page 92... ...
Accordingly, the Navy has changed to a 3 per cent coating which has met with much greater pilot acceptance and seems to involve only a nominal loss of protection. While fixed-filter goggles might provide adequate protection against retinal burns and flash blindness, they do impose a penalty of loss of vision because of the low transmittance of the filter.
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From page 93... ...
Flash blindness protective devices, as they are delivered into the fleet, represent a class of equipment entirely new to pilots. These devices attempt to meet a requirement for which no previous equipment has been provided.
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From page 94... ...
With this source it is possible to produce all of the features of flash blindness; that is, startle, intense afterimages, and visual incapacitation, without the risk of permanent damage to the visual system. By actually experiencing flash blindness, a pilot will better appreciate the need for protective devices and should be more highly motivated to use them correctly.
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From page 95... ...
Although such a weapon flash can also cause retinal burns, this paper is limited to the nature of the radiation in relation to flash blindness. The minimum information about a light source necessary to determine whether or not it will produce flash blindness, and, if so, to design adequate flash blindness protective devices consists of the luminance, duration, and visual angle subtended by the source.
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From page 96... ...
The variation of the ranges with weapon size is shown in Fig.
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From page 97... ...
Figure 4 shows the thermal history of a nuclear detonation at low altitude. The form of this curve -- a very rapidly rising and falling pulse followed by a second, longer, slower rising and falling pulse -- is the same for all weapons regardless of weapon size.
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From page 98... ...
6. The luminances of the smaller weapons viewed at the minimum safe distances exceed the luminance of the sun.
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From page 99... ...
6. Fireball luminance for five weapon yields at minimum safe distance with 80 per cent atmospheric transmission.
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From page 100... ...
7. Integrated fireball luminances for five weapon yields at minimum safe distances with 80 per cent atmospheric transmission.
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From page 101... ...
9. Visual angles subtended by fireball of five weapon yields at minimum safe distances.
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From page 102... ...
11. Integrated fireball illuminance for five weapon yields at minimum safe distances and integrated luminance of 10 per cent reflecting surface at 80 per cent atmospheric transmission.
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From page 103... ...
With reasonable knowledge of the luminance that personnel may be expected to encounter in operational situations, adequate flash blindness protection will be devised, and the minimum safe distance for personnel will not have to be extended. REFERENCES Glasstone, S
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From page 104... ...
One approach to the problem is to attempt field tests of visual function and visual impairment in conjunction with atomic weapon tests. Field tests may provide valuable information relative to the effectiveness of protective devices and general reactions to weapon detonation, but they can 104
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From page 105... ...
These considerations all argue for the study of basic visual functions which relate to flash blindness in the laboratory. Field tests, if they are ever again permitted, will afford a knowledge of the physical conditions to be encountered and will permit evaluation of protective devices and techniques, but information on the responses of the eye, from which necessary characteristics for protective devices can be specified, is best obtained in laboratory experiments.
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From page 106... ...
Flash duration is an important variable and a subsequent section is devoted to it, but in this section, flash duration is considered a constant. A hypothetical relation between the energy of an adapting flash and recovery time for a specific visual task is illustrated in Fig.
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From page 107... ...
provided a measure of the duration of flash blindness. Miller presented her data in the form of recovery time versus log adapting-flash energy in troland-seconds.
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From page 108... ...
3) , which, when replotted in terms of recovery time versus log adapting-flash energy, show an approximately straight-line relation between these variables over a wide range.
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From page 109... ...
3. Recovery times for detection of criterion targets after exposure to adapting flash as measured by several investigators.
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From page 110... ...
. In summary, several experiments have been performed that provide a relation between recovery time and the energy of an adapting flash.
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From page 111... ...
This characteristic of the curves is attributed to retinal injury which will be dependent solely on the characteristics of the adapting flash. It is possible, of course, that the effect of injury on recovery time will vary with the criterion task, but for a given task with changes only in display luminance, the relations presented in Fig.
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From page 112... ...
As display luminance is reduced, detection time increases at an increasing rate down to a display luminance which represents the absolute threshold for the discrimination of the display pattern. At high display luminances, there is little difference in recovery time for different adapting luminances, although recovery time is slightly longer for the two highest adapting luminances.
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From page 113... ...
6. Specification of the visual task in terms of acuity requirements is not sufficient to define the function, however, as visual acuity is an arbitrary and incomplete description of any visual display (Brown, Phares, & Fletcher, 1960)
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From page 114... ...
The form of the function showing recovery of visual acuity with time in darkness was not affected by duration of light adaptation, but appeared to be determined by the product of the luminance and duration of the light-adapting flash, i.e., the total luminous energy. In the experiment by Miller (1964)
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From page 115... ...
When an adapting flash is of the order of 1 ms duration or less, bleaching cannot be as great as that which will occur for the same or even lesser amounts of light energy spread out more in time. Early thresholds measured after a short adapting flash will, therefore, not be elevated as much as those after a longer duration.
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From page 116... ...
The curves of recovery time versus adapting-flash energy all indicate a more rapid recovery from a short adapting flash (165 jisec at one-third amplitude) than from a long adapting flash (9.8 ms at one-third amplitude)
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From page 117... ...
will have important implications for the theory of visual function. Spectral Characteristics of Flash and Task Illumination Some studies of flash blindness with various wavelength distributions of the adapting flash have been made, but they have been limited to low-flash energy levels by the use of selectively absorbing color filters for control of spectral distribution.
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From page 118... ...
. If the protective filter attentuates only the adapting flash and not the illumination of the visual task, shorter wavelength transmittance is bound to be accompanied by an increase in detection time for a coarse grating at low levels of illumination of the 118
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From page 119... ...
It is difficult to predict the result of investigations in which spectral variations are included. These results depend on the population of receptors required for the visual task, the threshold luminance for performance of the task, the spectral character and the energy of the adapting flash, as well as the spectral character and the luminance of the visual task illumination, and the spectral transmission characteristics of any filters employed.
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From page 120... ...
Although techniques of making measurements in flash blindness experiments differ from those which are usually employed in studies of dark adaptation, flash blindness experiments are essentially studies of the early dark-adaptation process following exposure to short adapting flashes. Rushton has found that the logarithm of threshold luminance during dark adaptation is an exponential function of elapsed time from the termination of light adaptation.
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From page 121... ...
(-1.4 log ft-L for visual acuity of 0.26; -2.3 log ft-L for visual acuity of 0.08.) Perception time t must approach a minimum tQ as display luminance L is increased, and it may safely be assumed that a value L will be reached beyond which there will be no further 121
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From page 122... ...
It varies both with the luminance of the adapting flash and with the visual acuity required by the display. Relations between average values of b determined graphically for JB and FS and the energy.
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From page 123... ...
The intersections of these vertical lines with the functions for each of the three grating display luminances provided coordinates in display luminance and recovery time with which to check the adequacy of Equation (3) for describing the results of Hill and Chisum.
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From page 124... ...
. This equation can be used to calculate values of adapting-flash energy at the longer flash duration, which would be equivalent to the shorter duration adapting-flash energy in their effects on recovery time, however.
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From page 125... ...
L Time required for detection of acuity targets following exposure to short adapting flashes.
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From page 126... ...
J The effect of varying the intensity and the duration of preexposure upon subsequent dark adaptation in the human eye.
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From page 127... ...
Some applications consider open transmission of major importance and demand a TABLE 1. Nominal Specifications -- Flash Blindness Protective Devices Transmission Density (activated)
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From page 128... ...
Mechanical Polarization Chemical-molecular Blink response ELF (explosive) Stressed plate Photochromic or Eye patch Electromechani Kerr Cell phototropic Fixed Filter cal goggles Pockle Cell chemicals Curtain Photochromic glass Destruction Triple-State enzymes of mirror F -centers surfaces Fast plating Exploding wire Vado materials 128
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From page 129... ...
Though limited to a maximum open transmission of about 30 per cent, closure time can be less than 1 ^sec. The Pockle Cell is approximately the solid-state equivalent of the Kerr Cell.
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From page 131... ...
Energy for the xenon flash-tubes is furnished by a high-efficiency power supply which is triggered by a light-sensitive detector circuit, which, in turn, reacts to the very earliest nuclear light. The size of the power supply is a function of the sensitivity of the photochromic material, the goggle area, and the closed density.
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From page 132... ...
2-10 2 5-10 Recycle rate (sec) 2-10 2 10 Life cycles 100 30-60 30-60 Optical quality All excellent fication is equalled by the periscope device and exceeded by the goggles, while the closure time exceeds the specification in both cases.
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From page 133... ...
In addition, the photochromic materials are temperature sensitive in that the clearing or reopening time varies with temperature. Another problem is weight, particularly that of the energy storage power supply.
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From page 134... ...
The concept of a goggle-type protective device should not be completely discounted since there will be other operations associated with flying in which they could be most valuable. The problem of flash blindness and that of chorioretinal burns cannot be entirely divorced.
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From page 135... ...
. It is apparent that there has been much effort expended in the past on the problem of chorioretinal burns; however, data obtained in these field tests and laboratory studies are of definite importance in establishing eye-protection criteria.
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From page 136... ...
These were parallel developments at the USAF School of Aerospace Medicine and the Aerospace Medical Research Laboratory. The phototropic approach has resulted in at least three eye-protection systems, including the indirectly activated phototropic goggles (Barstow & Lilliott, 1961)
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From page 137... ...
This model will made use of the best available data on recovery times and weapon illuminances, and if successful, will permit computer programming for development of flash blindness safe separation distance charts. Concurrent with the development of flash blindness separation distance charts will be the development of design criteria for eye-protective devices.
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From page 138... ...
R Radiation thresholds for chorioretinal burns.
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From page 139... ...
E Visual recovery times from high intensity flashes of light.
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From page 140... ...
BioTechnology, Inc. Relative to the flash blindness problem area, a flash blindness indoctrination and training device has been developed for the Office of Naval Research and the Bureau of Naval Weapons by BioTechnology, Inc.
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From page 141... ...
This panel provides tasks for the pilot which are representative of those performed by aviators. It can be used to demonstrate the performance decrement which occurs following exposure.
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From page 142... ...
TABLE 1. Range of Visual Recovery Times for Two Conditions of Illumination of the Visual Task Illumination Range of recovery times 0.5 foot-candles 20-90 sec 30 foot-candles 4-7 sec 142
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From page 143... ...
VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT James W Miller, Chairman
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