The design and utilization of a light stability cabinet for testing pharmaceuticals has been described. The lighting system developed for this cabinet is intended to simulate ordinary room illumination found in the pharmacy, home, doctor's office, or in other storage areas for pharmaceuticals, but under accelerated light intensity. The use of this equipment eliminates the influence of certain wavelengths in the ultraviolet spectrum of artificial sunlight testing equipment presently in use. Several representative pieces of artificial sunlight testing equipment used in the textile and dye industries are discussed. The photosensitivity of two tablet preparations were studied utilizing the specially designed light stability cabinet. Samples were stored in an open dish and in amber bottles. In one case the tablets contained a sulfonamide which darkened, while the other tablets contained a benzothaidiazine derivative plus D&C Orange No. 3 which showed fading of the color with storage. It was demonstrated that the amber glass appears to inhibit the deleterious effects of light on the tablets.