The right light, at the right time.
Meet Seize Light — it reads the sun above you and shows your two windows each day: when to get light, and when the sun can make vitamin D. Then it turns the daylight your Apple Watch records into a score you build on.
Coming to the App Store · iPhone & Apple Watch
Most sun apps show one number.
This one shows your day.
UV index is a single number. Seize Light turns it into the two moments that matter — when to get light to set your clock, and when the sun is high enough to make vitamin D — and scores how much daylight you actually got.
A light day that updates by the minute
Your place and the sky set the sun's path; the vitamin-D window opens when the sun climbs past about 45°. Each session estimates the vitamin D you're making — and counts you down to a safe stop, well before a burn.
Window opens in 1h 20mHow it works
Where you are and the sky above you become the right light at the right time — every value shown with the science behind it.
Find the sun
Your location and the clock place the sun's real path — sunrise, solar noon, sunset — computed right on your device.
Read the sky
Live UV index and cloud cover from Apple Weather tell you how strong today's sun is, where you actually are.
Your two windows
Get morning light to set your clock; step into the vitamin-D window when the sun is high enough — dose before burn.
Score your day
Your Apple Watch's Time in Daylight feeds a daily light score and a streak. Watch it move as your days change.
Your light, your phone
No account. UV comes from Apple Weather, not a sensor; the vitamin-D and sun math runs on your device. Your Health data stays on your device and your own private iCloud — never shared with advertisers. The app is free, supported by ads; a one-time purchase removes them.
- The vitamin-D & sun math runs on your device
- Only a coarse location is sent — for the weather
- Your Health data never leaves your device
- Estimates for wellness — never medical advice
"Carpe lucem." Seize the light.