Prophylactic treatment of seasonal affective disorder (SAD) by using light visors: bright white or infrared light?

Background: Thirty-eight patients with SAD participated in a light visor study addressing two questions. 1. Can the development of a depressive episode be prevented by daily exposure to bright light started before symptom onset in early fall and continued throughout the winter? 2. Does the light have to be visible in order to have beneficial effects? Abstract Methods: Three groups participated in the study: I (n = 14) received bright white light (2500 lux); II, (n = 15) received infrared light (0.18 lux); III (n = 9, control group) did not receive any light treatment at all. Results: Infrared light is just as effective as bright white light. Both are more effective than the control condition. Conclusions: Light visors can be effectively used to prevent the development of SAD. The fact that exposure to infrared light was as effective as exposure to bright white light questions the specific role of visible light in the treatment of SAD.