(CIE, Commission Internationale de l'Eclairage) The International Commission on Illumination. It is the international organization that is responsible for establishing the chromaticity diagram of 1931. The three dimensional 1931 CIE diagram attempts to define light and color. Only two of the three dimensions are represented in this program. There have been several important systems developed by the CIE since 1931. We sort of skip the chart developed in 1969 and go directly to the one put forth in 1976. CIELUV units come from that representation. While the 1976 chart more accurately represents the way we see light, the tradition of using the numbers in the 1931 system still continues. Both systems are represented on this web site.