Because medications for bipolar depression are often ineffective and frequently produce adverse effects, nonpharmacological approaches hold great interest. Morning light in patients with bipolar depression has had mixed results and induces occasional hypomania. Based on preliminary work, investigators conducted a randomised, 6-week study comparing midday broad-spectrum bright-light therapy (7000 lux) with dim red light (a "sham" condition; 50 lux).

The 43 participants had moderate levels of bipolar depression with no manic symptoms and were on stable medications (mean age, 45; 67% female); 67% had bipolar I disorder, and 83% had some seasonality. Exclusions included manic, hypomanic, or mixed episodes within 6 months; rapid cycling in the past year; active psychosis, suicidality, or substance use disorder; and certain medical conditions.

Light therapy was daily between noon and 2:30 p.m., gradually increasing to a target of 60 minutes daily (median achieved length, 46 minutes). With most improvements occurring between weeks 4 and 6, 68% of those receiving bright light remitted at 6 weeks, compared with 22% receiving dim light. No hypomania, manic switches, or treatment-attributable serious adverse effects occurred.