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An instrument that measures the lowest brightness of an extended area that can barely be detected by the eye.



an apparatus for measuring the optical sensitivity of the eye by finding the minimum light intensity which creates a sensation of light; it is also used to study a number of physiological characteristics of sight, such as the course of adaptation to shadow and vision in twilight.

The design of the adaptometer ensures a smooth variation in the precisely measured intensities of light over a wide range (from 10 million to several hundred million times). When the adaptation to dark is studied over a long time (up to 60 minutes) the investigator seeks the dependence (generally expressed graphically) of the sensitivity of the eye to the interval of time spent in the dark.

In order to obtain a base value for adaptation (during three minutes), the investigator studies the variations of the brightness of colors in dusk visibility.


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