Bright light therapy is an effective treatment for seasonal affective disorder, an uncommon condition marked by mild winter depression. Bright lights have been used as adjuncts in the pharmacological treatment of other types of depressive illness. The rooms in our psychiatric inpatient unit are so placed that half are bright and sunny and the rest are not. Reasoning that some patients were getting light therapy inadvertently, we compared the lengths of stay of depressed patients in sunny rooms with those of patients in dull rooms. Those in sunny rooms had an average stay of 16.9 days compared to 19.5 days for those in dull rooms, a difference of 2.6 days (15%): P < 0.05.