(black) and scotopic[LINK: http://www.cvrl.org/database/text/lum/scvl.htm] [1] (green) luminosity functions. The photopic includes the CIE 1931 standard [LINK: http://www.cvrl.org/database/text/cmfs/ciexyz31.htm] [2] (solid), the Judd-Vos 1978 modified data [LINK: http://www.cvrl.org/database/text/lum/vljv.htm] [3] (dashed), and the Sharpe, Stockman, Jagla & Jägle 2005 data [LINK: http://www.cvrl.org/database/text/lum/ssvl2.htm] [4] (dotted). The horizontal axis is wavelength in nm.]] The candela (, symbol: cd) is the SI base unit of luminous intensity (that is, power emitted by a light source in a particular direction, weighted by the luminosity function, a standardized model of the sensitivity of the human eye to different wavelengths). Definition Since the 16th General Conference on Weights and Measures in 1979, the candela has

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