The Short Version
Apple Watch has quietly tracked daily sunlight exposure using its ambient light sensor since watchOS 10 launched in 2023, with years of data stored and searchable in the Health app.
Apple buried a genuinely useful health tool so quietly that it took three years for most people to find it. Since 2023, your watch has been logging daily sunlight time without ever asking for permission or announcing itself. Apple tracks your sun exposure more reliably than you track your own screen time. Check the Health app search bar before assuming your watch is just a step counter.