Patent ID: 7322731

Claim:
An optical system, comprising: an image-forming panel having an illumination side; and a backlight unit disposed to the illumination side of the image-forming panel, the backlight unit comprising: at least first and second light sources, the first light source producing light at a first wavelength and the second light source producing light at a second wavelength different from the first wavelength, and a reflecting cavity having at least one reflecting surface and a controlled transmission mirror, the light from the first and second light sources being reflected within the reflecting cavity, the controlled transmission mirror comprising an input coupling element, an output coupling element and a first multilayer reflector between the input and output coupling elements, the first multilayer reflector being reflective for normally incident light from the first and second light sources, the input coupling element redirecting at least some of the light propagating from the first and second light sources in a direction substantially perpendicular to the first multilayer reflector into a direction that is transmitted through the first multilayer reflector.