Dim versus bright red (light-emitting diode) light in the treatment of seasonal affective disorder

Forty-three subjects with seasonal affective disorder were randomly assigned to receive 2 weeks of treatment with either bright- (mean 4106 lx) or dim-light (mean 96 lx) therapy, using red light-emitting diode light sources, in a head-mounted unit. Defining response as a 50% reduction in the 21-item Hamilton Depression Rating Scale score to a post-treatment score of less than 8, there was no significant difference in response rate between patients receiving bright light (67%) as compared with patients receiving dim light (68%). Possible explanations for the similar response rate to 2 very different illuminances of red light are discussed.