Morning light is the real driver for SAD, but evening blue blockers help

Blue-light blocking glasses in the evening are effective as a supplement to morning light therapy for late-winter SAD, but they won’t do much alone.

The mechanism here is circadian timing. Late-winter SAD is largely about your internal clock drifting late because you’re not getting enough bright morning light. Morning light therapy (10,000 lux, white light with blue wavelengths) resets that clock forward — that’s the main treatment.

Evening blue blockers help by preventing that clock from drifting even later. Blue light after sunset suppresses melatonin and tells your brain it’s still daytime. Blocking it ~2-3 hours before bed improves sleep onset and sleep quality, which indirectly helps mood