Light therapy can be an effective treatment for seasonal depression, but there has been concern that the treatment might induce mania in people with bipolar disorder. Participants in the new trial did not experience any manic episodes, despite daily exposure to bright light.

The study was led by 2013 and 2002 Young Investigator Dorothy K.Y. Sit, M.D., and 1998 Independent Investigator Katherine L. Wisner, M.D., M.S., both at Northwestern University.

Forty-six patients participated in the study. All had been diagnosed with bipolar disorder and were taking medication to manage the illness. At the time of the study, which for most participants began in the fall or winter, all patients were suffering from an episode of moderate depression.

Trial participants were randomly assigned to receive daily treatments of either bright white light or dim red light, with the red light serving as a placebo. Treatments were administered midday, beginning with 15 minutes of light exposure and increasing daily until treatments reached a duration of one hour. The light dose was similar to that used to treat seasonal affective disorder.

After six weeks of treatment, 68 percent of those who received bright light therapy experienced a remission of their depression. In contrast, only 22 percent of those in the placebo group achieved remission.

In an earlier study involving some of the same patients, Dr. Sit and colleagues tested the effects of administering light therapy in the morning, and found that some patients responded with episodes of mania. Timing of light exposure may be critical for managing depression in patients with bipolar disorder, they say.