From PanoTools.org Wiki

Radiance RGBE is a HDR image format[*] invented by Greg Ward Larson for his Radiance rendering software. The file extension is usually .hdr. It stores pixels as one byte RGB (red, green, and blue) values with a one byte shared exponent. Thus it store four bytes per pixel and the dynamic range covers 80 decades.

Retrieved from "http://wiki.panotools.org/index.php?title=RGBE&oldid=9530[*]"