Reference image brightness width
The reference image brightness width (RHB) is a measure of the brightness of a projected image on a projection screen. It depends on the light output of the projector, specified in ANSI lumens, and the size of the image projection.
The reference image brightness width was developed for comparability of projectors with different light output levels. As a reference, 1,000 ANSI lumens were chosen and an image width of 2 m was selected. With an aspect ratio of 4:3, this results in a projection area of 3 square meters and a projection screen brightness of 333 lux.
This relationship illustrates that projection brightness is directly dependent on the size of the projection surface. Thus, a doubling of the area results in a halving of the brightness, and with twice as much light output, twice as large an area can be illuminated with the same projection brightness.