Seize Light

Most sun apps show today's UV. Seize Light shows your two windows — when to get light and when to stop — and scores your light day from your Apple Watch.

Get the right light at the right time. Seize Light reads where you are and the sky above you, computes the sun's real position on your device, and shows your daily light windows — when to get outside, and when to wind down.

Most sun apps just show today's UV number. Seize Light shows your two windows: a morning-light window to help set your body clock, and the vitamin-D window — the part of the day the sun is high enough to make vitamin D — plus an evening wind-down to help protect your sleep. Your Apple Watch's Time in Daylight turns it into a passive daily habit, with a transparent Light Score and a streak.

YOUR THREE WINDOWS • Morning light — get outside soon after waking to help set your clock; today's target minutes adjust for cloud cover. • Vitamin-D window — opens when the sun is high and UV is strong enough, and closes when it isn't (it tells you why). Keep it short and sub-erythemal. • Evening wind-down — when to dim the lights and protect your sleep.

THE LIGHT SCORE A simple, transparent 0–100 score from three parts — morning light, daylight total, and evening protection — fed by your Apple Watch's Time in Daylight. Missing data is never held against you. Build a daylight streak and watch your 90-day trend.

EVERY NUMBER IS CITED The solar math, the UV model, and the vitamin-D estimate all trace to published science in an in-app "How this works" screen.

HONEST BY DESIGN • UV comes from weather-forecast data (Apple Weather), not a sensor. • Vitamin-D output is an estimate from a model, not a blood test. • Sun safety first: protection is advised at UV 3+, and the rule is always — don't burn. • General wellness and educational use only — not medical advice. Consult a healthcare professional before making health decisions.

PRIVATE BY DESIGN • No account. No sign-up. No ads, no tracking. • The solar and vitamin-D math run on your device; only coarse coordinates are sent, for the weather lookup. • Health data is read-only and never leaves your device, except to sync through your own private iCloud.

Weather data provided by Apple Weather.

Carpe lucem. Seize the light.