Spectral energy distribution of the International Commission on illumination light sources A, B and C

Standard ligh t sources A, B , and C were adopted by the International Commission on Illumination (CIE) in 1931 for t he colorimetry of materials. Source A is an incandescent lamp operated at 2,854 K . Sources Band C, r eprese ntative of average noon s unlight and average daylight, respectively, are produced by passing radiant flux from source A through specified Davis-Gibso n filters described in Bureau Miscellaneous Publication M114 (