Light therapy for preventing seasonal affective disorder.

Single-centre, randomized, non-blinded controlled trial conducted in the Netherlands; 46 adults with a history of SAD who were non-depressed at baseline; outpatient setting; three-arm design: bright white visor light, infrared visor light, and no light exposure.

Bright white visor light: 2500 lux, 30 minutes daily in the morning (6:00–9:00), at home, during October–April across two winters (1993–1994 and 1994–1995). Infrared visor light: 0.18 lux, 30 minutes daily in the morning (6:00–9:00), at home, during October–April across two winters (1993–1994 and 1994–1995).

Light therapy reduced winter SAD incidence numerically versus no light therapy in this small RCT, but confidence intervals were wide and the evidence quality is very low. No adverse events were reported. There is no comparative evidence versus other preventive options. Conclusion: efficacy and safety remain uncertain; decisions should be guided by patient preferences; more high-quality trials are needed.

Small sample size; single study; high risk of bias (unblinded, incomplete data, self-rated outcomes); no adverse event data; limited participant characteristic reporting; older visor-light intervention with limited generalizability; very wide confidence intervals.