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There are two luminous efficiency functions in common use. For everyday light levels, the photopic luminosity function best approximates the response of the human eye. For low light levels, the response of the human eye changes, and the scotopic curve applies. The photopic curve is the CIE standard curve used in the CIE 1931 color space.
The scale consists of 20 colors [1] (from light blue to dark brown-black) that correspond to the different eye colors observed in nature due to the amount of melanin in the iris (in this case, the lower the number, the lighter the eye color): [2] [3] 1-2: blue iris (1a, 1b, 1c, 2a : light blue iris - 2b: darker blue iris) 3: blue-gray iris
The original Martin scale, summarized below, consists of 16 colors (from light blue to dark brown-black) that correspond to the different eye colors observed in nature due to the amount of melanin in the iris. The numbering is reversed in order to match the Martin–Schultz scale, which is still used in biological anthropology. In this case ...
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The use of the human eye as a detector led to photometric units, weighted by the eye's response characteristic. Study of the chemical effects of ultraviolet radiation led to characterization by the total dose or actinometric units expressed in photons per second. [1] Many different units of measure are used for photometric measurements.
Some clinics do not have 6-metre eye lanes available, and either a half-size chart subtending the same angles at 3 metres (9.8 ft), or a reversed chart projected and viewed by a mirror is used to achieve the correct sized letters. In the most familiar acuity test, a Snellen chart is placed at a standard distance: 6 metres.
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Three hues in the Munsell color model. Each color differs in value from top to bottom in equal perception steps. The right column undergoes a dramatic change in perceived color. Lightness is a visual perception of the luminance of an object. It is often judged relative to a similarly lit object.