Sundog vs Seize Light

Most people either avoid the sun entirely or stay out too long. Sundog helps you do neither. Built around four science-backed goals, Sundog gives you a personalized daily sun schedule — calibrated to your skin type, the live UV index, and real-time cloud cover. A smart timer tells you exactly how long to be outside, and your burn limit is always visible so you know when to head back in. Four Goals. One Routine. - Circadian Reset — Morning light sets your body clock for the day. A short session before 9am resets your sleep-wake rhythm, lifts mood, and sharpens focus. - Vitamin D — Midday UVB is your window. Sundog times your session to maximize D synthesis and stops automatically before you reach your burn limit. - Gradual Tan — Afternoon light has lower UV intensity. Sundog schedules your exposure when the risk is lowest and the result is real. - Sleep Optimization — Evening golden-hour light cues melatonin production, making it easier to fall asleep and stay asleep. Smart, Not Just Simple Sundog's timer isn't a countdown — it's a calibrated recommendation. It reads the live UV index and adjusts your session length automatically. Heavy cloud cover? Session extended. UV extreme? Pulled back. Your burn limit is always front and center. Built Around Your Skin Set your Fitzpatrick skin type once. Sundog uses it to calculate your personal burn limit at any UV level and adjust every session recommendation accordingly. Skin type I gets very different guidance from skin type V. Time-Window Gating Each goal has a scientifically appropriate time window. Circadian Reset is a morning-only session. Vitamin D is gated to the midday UVB window. Sleep Optimization surfaces in the evening. You always know whether your window is open, closing soon, or already passed for the day. Sun Tracker A visual emoji-based tracker shows your progress across the day — which sessions you've completed, which are still open, and what's coming up next. Daily Sun Insights Every day, Sundog surfaces a new insight — practical, evidence-based tips on UV, circadian biology, and getting more from your time outside. Available in English and Spanish. Sundog is designed for general wellness purposes only. It is not a medical device and does not provide medical advice. Consult a qualified healthcare professional before changing your sun exposure habits, particularly if you have a skin condition, a history of skin cancer, or are taking photosensitizing medications. UV exposure carries inherent risks. Always use appropriate sun protection.

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 that tells you when to dim the lights. 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 as part of a wind-down routine. 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. • 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 — and it is never used for advertising. Weather data provided by Apple Weather. Carpe lucem. Seize the light.