Indoor products may be subjected to a wide range of interior lighting environments. These environments include residential incandescent, commercial fluorescent, and industrial metal halide illuminants. Products may also be exposed to sunlight coming through a window or an automobile windshield. Each of these light sources has its own unique spectrum. In a like manner, each material has its own unique spectral sensitivity. This paper surveys a wide variety of the most commonly used indoor light sources, including direct and indirect window-filtered sunlight. The results indicate that direct window-filtered sunlight is the most severe interior lighting condition that your product will probably see. Because a xenon arc test chamber can provide an excellent simulation of sunlight through window glass, it is the best method of simulating this worst-case indoor lighting environment for testing the light stability of your product.