Relative luminance follows the
photometric definition of luminance, but with the values normalized to 1 or 100 for a reference white. Like the photometric definition, it is related to the luminous flux density in a particular direction, which is radiant flux density weighted by the
luminosity function ![](http://info.babylon.com/onlinebox.cgi?rt=GetFile&uri=!!ARV6FUJ2JP&type=0&index=3130)
of the CIE Standard Observer.