Abstract: A sign having selectable spectral characteristics of visible light produced by combining selected amounts of light energy of different wavelengths from different sources in a diffusion chamber. The signs exhibit diffuse reflectivity to provide light having uniform intensity and illumination.

Abstract: A signage system to provide advertising and the like. In a first example, the sign includes a cavity in a housing with a diffusely reflective interior surface at the back of the housing and a sign panel at the front of the housing with an aperture for allowing emission of light from the cavity. In still another example, the sign is a channel letter with a clear or translucent sign panel and with light sources mounted on a shelf facing the back of the housing. The light sources preferably use LED's or other solid state devices. Where the light sources emit multiple wavelengths, control of the intensity of emission of the LED light sources determines a spectral characteristic of the light output through the aperture.