Relative luminance Y {\displaystyle Y} follows the photometric definition of luminance L {\displaystyle L} including spectral weighting for human vision, but while luminance L {\displaystyle L} is a measure of light in units such as c d / m 2 {\displaystyle cd/m^{2}}, Relative luminance Y {\displaystyle Y} values are normalized as 0.0 to 1.0, with 1.0 being a theoretical perfect reflector of 100% reference white.
