Your light box needs to work harder above 50°N

Living at high latitudes like above 50°N lowers your threshold for seasonal affective disorder in late winter, and yes, you likely need more intense or longer light exposure to compensate.

The mechanism is simple: less light, more trouble. At 50°N (roughly London, Berlin, Calgary) the winter sun barely clears the horizon, and by 60°N (Oslo, Anchorage) you’re dealing with just a few hours of weak, angled light. Late winter — February through March — is actually the worst time for SAD at these latitudes because you’ve already been starved for months. Even though days are getting longer, your circadian system is still playing catch-up, and the absolute amount of bright light hitting your retinas stays low.

The standard recommendation — 10,000 lux for 30 minutes — works fine for most people at mid-latitudes. But above 50°N, I’ve seen clinicians suggest bumping that to 45 or even 60 minutes in late winter, and some people need a stronger box (closer