LBNL Report Number
For several generations lighting practitioners have had suspicions that calibrated light meters and photometers do not accurately reflect their perceptions of lit environments even for light which is whiteish in color. The troublesome perceptions arise when comparing lightings of different spectral quality and where the metered photometrics are equal but contrarily where brightness sensation and visual sensitivity are perceived to be different. An observer can readily experience these perceptions of different lightings by comparing the same environment under equally lit photopic conditions by low color temperature lamps (3000 K) versus high color temperature lamps (6000 K) or incandescent lighting versus natural lighting or compare high pressure sodium lighting with metal halide lighting. Vision scientists have tried to resolve this problem by introducing small corrections into the calibration function which are not included in its classic determination based on flicker photometry. These refinements have not resolved the differences and the problem continues to plague lighting practice.