Bright light and high-density negative air ionization reduces symptoms of seasonal affective disorder.

Intervention Patients were allocated to 6 groups for 2 consecutive treatment periods, each lasting 10–14 days. 2 parallel groups received morning treatment with negative ions. 4 groups received light treatment and were crossed over at mid point using the following sequences: morning-evening, evening-morning, morningmorning, and evening-evening (10 000 lux, 30 min/d). 2 groups received negative air ionisation treatment at either high density (2.7 x 10) or low density (serving as the placebo control, 1.0 x 10 per cubic centimeter) (high-high and low-low sequences, 30 min/d in the morning). All treatments lasted for 20–28 days with a 1–3 week withdrawal phase.