A convenient linear scale for measuring, in arbitrary units, the relative luminance amplitudes within the scene to be recorded in a video or photographic image, as shown below. The relative luminance scale is one factor affecting the choice of suitably artistic scene reproduction. It may establish the optimum rendition of reference white and optimum employment of the nonlinear transfer function in image recording.

Note: This relative luminance scale (linear in luminance) resembles IRE units (linear in voltage) in positioning both black level reference and reference white at 0 and 100, respectively, but that it differs in recognizing the extended luminance range of many commonly encountered scenes.