Global illumination methods allow us to calculate physical values such as radiance and luminance at each pixel, but they do not tell us how to display these values. If we attempt to fully reproduce the world luminance levels on a computer monitor, slide or print, the results are usually disappointing, for a couple of reasons. First, contemporary display media fall short of the real worlds dynamic range by a few orders of magnitude. It isn't possible to reproduce the luminances in bright and dark regions accurately. Second, the adaptation luminance, or light level to which the viewer is accustomed, is almost always different under the real world and computer display viewing conditions, and this affects visual response dramatically.