Skot (unit)

Skot (symbol: sk) is an old and deprecated measurement unit of luminance, used for self-luminous objects (dark luminance). The term comes from Greek skotos, meaning "darkness".

Overview
The skot to measure the dark luminance (Dunkelleuchtdichte) was introduced in 1940 by the German Lighting Society (Deutsche Lichttechnische Gesellschaft, LiTG) out of a necessity to describe the luminance of self-luminous objects, which differed so much from that of other objects that it was impractical to describe it using commonly used luminance values. Conversion factors for so called "scotopic stilb" (Skotopisches Stilb) depend on the spectral distribution of the light and were therefore redefined in 1948 by the International Commission on Illumination (Internationale Beleuchtungskommission, IBK) for a specific color temperature of 2042 K or 2046 K, the temperature of solidification of platinum. Before 1948, the definition was based on a temperature of 2360 K as emitted by a wolfram-vacuum lamp. At this temperature, 1 sk = 10−3 asb. The maximum allowed value is 10 skot to avoid the unit being used up into areas of mixed scotopic and photopic vision of the eye.