Comparison

Rays vs Seize Light

Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.

Head to head
About

Rays

Automatically tracks your body's vitamin D synthesis from sun exposure. Get personalized recommendations for optimal timing and duration to maintain energy, mood, and skin health year-round without manual logging.

Highlights
  • Automatic vitamin D synthesis tracking
  • Personalized health intelligence
  • Smart sun exposure recommendations
  • Progress tracking and health insights
  • Apple Health integration
  • Minimal battery usage
Read full description

Never Worry About Vitamin D Again Over 1 billion people are vitamin D deficient, but knowing if you’re getting enough sun shouldn’t be complicated. Rays is the world’s first app that automatically tracks your vitamin D synthesis, so you can spend your time enjoying life. No manual logging, no thinking required. Why Vitamin D Matters Optimal vitamin D levels support natural energy, balanced mood, healthy sleep cycles, and radiant skin. With Rays’ precise tracking, you can maintain these benefits year-round without guesswork or overdoing it. Automatic Vitamin D Tracking Rays uses a first-of-its-kind outdoor detection system combining GPS precision patterns, sensor data, movement analysis, and personalized machine learning that adapts to your routines. With high accuracy and minimal battery usage, it works seamlessly in the background without any manual input. Personalized Health Intelligence Our algorithm analyzes your skin type (Fitzpatrick Scale I-VI), age, geographic location, supplement intake, and lifestyle factors. Based on Endocrine Society Clinical Practice Guidelines, we provide recommendations as precise as your doctor’s, but as convenient as checking the weather. Smart Recommendations Receive personalized guidance like “Get 18 minutes at 11 AM tomorrow” based on real-time UV index, cloud cover, solar positioning, and your personal synthesis rate. Our intelligent engine suggests optimal timing when UV will be 2-3x more efficient for vitamin D production. Advanced Progress Tracking Monitor your vitamin D synthesis with detailed weekly charts, streak tracking, and comprehensive health insights. Seamlessly syncs with Apple Health and automatically adjusts for seasonal variations while preventing excessive intake when combined with supplements. For Tanners & Sun Enthusiasts Already spending time in the sun for a tan? Put that exposure to work. Rays tracks your cumulative UV dose so you can optimize your color, avoid overexposure, and know exactly where you stand — all automatically. Rays is perfect for health-conscious individuals who want optimal vitamin D without the guesswork. Try Rays free for 3 days with full access to all features. Terms of Use: https://getrays.app/eula Privacy Policy: https://getrays.app/privacy Health Disclaimer: https://getrays.app/health-disclaimer

About

Seize Light

Features
Read full description

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.

Screenshots

Rays4 screens
Seize Light4 screens

Verdict

The call

The clearest difference is in-app purchases: Seize Light at none against Rays's 2. Rays's advantage is ads (none vs shown) and update cadence (every 5 days vs every 2 weeks). On price and device support there is nothing between them.

Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS

CostPrice · In-app purchases · Ads · Monetization

Both are free to download. Rays sells 2 in-app purchases, starting at $4.99 per month. Seize Light asks for nothing beyond the download.

UpkeepUpdate frequency

Rays ships an update every 5 days, Seize Light every 2 weeks. The most recent releases landed on October 24, 2026 and October 12, 2026 respectively.

Scorecard4 real differences · 6 level
Rays versus Seize Light: the parameters behind the verdict, then further details
ParameterRaysSeize Light
PriceFreeFree
Rating4.4 (7 ratings) — better—
Positive reviews75.0% of reviews—
Number of ratings7 — better—
Update frequencyEvery 5 days — betterEvery 2 weeks
AdsNo — betterYes
In-app purchasesYesNo — better
MonetizationFree with in-app purchases—
DevicesiPhone, iPod — betteriPhone
Requires iOS15.1 — better18.0
Further details — not scored
Size58 MB35 MB
Age rating4+4+
DeveloperRays Health Technologies LLCsebastian totte

In-app purchases

2 purchases

Rays

Subscriptions2
  • Rays - Auto Vitamin D Tracker3 Days trial$4.991 Month
  • Rays - Auto Vitamin D Tracker3 Days trial$19.991 Year
None

Seize Light

No in-app purchases

Questions

Is Rays free?
Rays is free to download, with in-app purchases available.
Is Seize Light free?
Seize Light is free to download, with no in-app purchases.
Do Rays or Seize Light have ads?
Seize Light shows ads; Rays does not.
Which is updated more often, Rays or Seize Light?
Rays ships an update every 5 days, and Seize Light every 2 weeks. Most recently, Rays was updated on October 24, 2026 and Seize Light on October 12, 2026.

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