Seasonal Light Loss and Winter Headache Patterns
A winter light headache is usually driven by two separate changes, not one. The first is light quantity — indoor winter light sits somewhere around 100 to 500 lux, while even a heavily overcast outdoor day delivers several thousand, so most people spend the dark months receiving roughly an order of magnitude less light than their circadian system evolved to expect. The second is light timing — a later sunrise moves the signal that sets your body clock, which drifts sleep and melatonin release later and leaves you running a mild, permanent jet lag. Both can lower the migraine threshold. They respond to different fixes, and neither is the same thing as seasonal depression.
The distinction matters, because a lamp only fixes one of them, and only if you use it at the right hour.