Photostability chambers provide high intensity lighting in the 300-700 nm range for pharmaceutical stability studies conducted at constant temperature (25°C) according to the ICH testing guidelines. Each shelf has a bank of 10 lights that produce uniform lighting (±10%) across a large circular area on the shelf. The banks combine black and cool white fluorescent bulbs to satisfy the ICH definition for Option 2 lighting. At a distance of about 8” from the lights, average light intensity is approximately 10,000 lux for visible light and 10 w/m2 for black light. Four light switches control the light banks, and a black light digital timer allows the black light portion of the testing to be curtailed while the visible light portion of the stability study continues to completion. Temperature failsafes and lockable solid doors protect the study from temperature excursions and light disruption.