A reader asks:

Are light visors effective in treating SAD? I have found one that emits 2500 lux. Is this light output strong enough to counteract SAD?


In principle, 2500 lux from a visor should be effective, although it would require far longer daily exposure duration (around 2 hours) than using a 10,000 lux light box (around 30 minutes). Such lower light levels were typical of first-generation light boxes that gained wide use about 15 years ago. However, attempts to demonstrate visor efficacy for treating winter depression have been hampered by the failure of controlled studies to show any benefit from low-level “placebo” light. The problem may lie in the narrow area of illumination projected by the visor, which could result in non-optimal illumination of the retina of the eye. Future design enhancements of visors may yet solve this problem.