Your phone is already a SAD light tracker

You don’t need a fancy wearable to manage Seasonal Affective Disorder in late winter—your phone’s light sensor and a free app can do the job just fine.

The key metric you want is lux-hours (brightness × time). Most light therapy lamps target 10,000 lux for 30 minutes, but optimizing natural daylight exposure works too. Apps like Light Meter (free, no ads) or Lux Light Meter Pro let you point your phone at your surroundings and get a reading. Take a few spot checks throughout the day: morning daylight near a window might hit 2,000–5,000 lux; your desk lamp might be 300. If you’re well below 10,000 lux total across the morning, that’s a sign to adjust.

Wearable light sensors (like the LYS or Ayo) are nicer if you want continuous logging without thinking about it. They clip to your shirt and record lux every few minutes. But honestly? Most people just need to know whether their morning routine is dim enough to stall their circadian rhythm. Open the curtains, eat breakfast near a window, take a short walk—that’s usually enough.

If you’re deep in late-winter blues and want to be systematic, use a habit tracker (like Streaks or Habitica) to log morning light exposure. Combine it with a light meter check. The real optimization is simple: get bright light within an hour of waking for at least 20 minutes. Technology just confirms whether you’re actually doing it.

Don’t overthink it. Your phone is already a light sensor. Use it.