Light can cause retinal damage by mechanical, thermal, or photochemical mechanisms. Mechanical and thermal injury require a very intense light exposure, but photochemical injury is caused by a prolonged exposure to light levels that probably would be well tolerated if experienced only transiently. The existence of photochemical retinal damage has prompted concern about its possible role in macular degeneration, and reexamination of the safety of clinical light sources. An analysis of the potential hazardousness of these light sources is presented, in addition to a review of retinal damage mechanisms, and suggestions for pertinent patient counseling.