Maybe this will help... Infrared is a portion of the invisible spectrum: the portion of the invisible electromagnetic spectrum consisting of radiation with wavelengths in the range 750 nm to 1 mm, between light and radio waves. It is the range between 750 and 900 nm that affest IR film. It's primary purpose was to help distiguish between collors that were really close in scientific work... Like the variations of green in a leaf. However once people like you and I stared palying with it, it bacame very popular as an artistic tool :)