Your latitude determines how much light you need.

Yes, latitude directly impacts SAD severity because winter daylight drops sharply the further you get from the equator, and treatment adjustments are mostly about compensating with more light.

At high latitudes (think Seattle, London, or Helsinki), SAD symptoms tend to be more intense and last longer because the days are genuinely dark. At 45°N you might get 9 hours of weak winter sun; at 60°N you’re looking at 5 or 6. That’s a big difference in how much your brain can reset its circadian clock naturally.

If you’re in Miami, a standard 10,000 lux light box for 20–30 minutes in the morning usually does the trick. But as you go North, you may need to bump that up, both in duration and maybe intensity. I’ve heard from people in the Pacific Northwest who run their light box for 45 minutes or combine it with a dawn simulator. Some also benefit from taking vitamin D more aggressively or adjusting the timing of their light exposure to match the sunrise.

That said, latitude isn’t everything. Your individual sensitivity