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Abstract
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Night vision or dark adaptation is a function of the nature of the visual stimulus and the physiological states of the viewer. Night vision efficiency varies on persons of the same age, among persons of different ages, and with the physiological state of the viewer. Low blood sugar levels, oxygen deprivation, co poisioning, and dietary deficiency all tend to reduce the final level of night vision and the time required to achieve it. Dark adaptation, recovery from light shock, visual acuity, depth perception and visibility under glare conditions were studied when the targets were seen through tinted windshield glass.
RESULTS were compared with those obtained with filters, or with filters of different absorptive properties. The tinted windshield glass used in these tests is an absorptive filter of light bluish- green tint with a transmission maximum near 500 millimicrons. Thresholds are about 0.15 log units higher in dark adaptation tests, when tinted windshield glass is used in front of the test light as compared with the condition when no filter was used. After a light shock, recovery time is 1.2 to 1.4 times longer when the test target is shielded by tinted glass windshield glass than when no filter is in front of the target. Visual acuity is less when a tinted windshield is placed between observer and target than when no filter is used. Depth perception tests with a verhoeff stereoptor yields about 25% poorer results when a tinted windshield is in the path of vision than when no filter is involved. When thresholds are determined at which targets at fixed angular distances from a glare source become visible, it is found that the ratios of glare luminance are the same. Test results cannot be interpreted as being favorable to the use of tinted windshields. Statistical analysis of a large sample ranging from 16 through 89 years of age indicates that age is the best known predictor of the eventual level of dark adaptation. Age, the initial level of adaptation, and the asymptotes of the cone and rod curve are reliably statistically correlated. The initial level of adaptation is negatively correlated with the asymptote of the asymptotes of the cone and rod curve, and the final level of adaptation, or the asymptote of the rod curve. |