OPSIN is a wellness tracker, not a medical device. Everything it shows —
vitamin D, UV dose, lux, and scores — is an estimate to help you build better
daily light habits. It does not diagnose, treat, or prevent any condition, and it is not a
substitute for a doctor, a blood test, or a calibrated UV/light meter.
The basics
What does OPSIN actually do?
OPSIN helps you get the right light at the right time. It estimates your daily
vitamin D from the sun (plus any supplements you log), tracks your circadian light exposure
(bright mornings, dim evenings), tells you the best times to go outside today, and warns you
before you'd get too much sun for your skin type.
How is OPSIN different from other sun / vitamin D apps?
Most apps optimize a single number. OPSIN models your whole light day from one
consistent engine — so your "safe sun limit" and your "vitamin D goal" are always calculated
from the same physics and never contradict each other. It combines vitamin D, circadian rhythm,
and burn safety into one picture, with a plan for when to go outside.
Is OPSIN free?
Core features are free. A Premium subscription unlocks the full recommendation
engine, all history and insights, unlimited light readings, the AI coach, and tracking tools.
You can cancel anytime; subscriptions are billed through your app store.
Accuracy & how it's calculated
How accurate are the vitamin D numbers?
They are modeled estimates, not measurements. We use published photobiology
(UV Index, your skin type, exposed skin, age, and the sun's angle) to estimate how much
vitamin D your skin can make — and we cap it at the point where skin physically stops making
more (the "plateau"). Real synthesis varies a lot between individuals (±30–50%), so treat the
numbers as a helpful guide, and confirm your actual status with a blood test (25-OH-D) if it
matters to you.
Why does the app sometimes say I've hit my safe limit but not my full goal — or vice versa?
This is exactly the kind of contradiction OPSIN is designed to avoid. Your skin
stops making vitamin D at roughly the same exposure where sunburn risk begins, so on most sunny
days "you've optimized your vitamin D" and "you've reached your safe limit" arrive together. On
weak-UV days (winter, high latitude, heavy cloud) the sun physically can't reach your target —
OPSIN will tell you that honestly and suggest topping up with a supplement rather than sending
you out to burn.
Where does the UV and weather data come from?
From a public forecast service (Open-Meteo). The UV Index we use already accounts
for cloud cover, so a cloudy day shows lower UV than a clear one. UV also depends on your latitude,
the season, time of day, and elevation.
Does the app's light meter (the "mirror") really measure lux?
It estimates it. On phones, the camera's own exposure settings (shutter, ISO,
aperture) encode how bright the scene is — that's what real light-meter apps read, and it's far
more reliable than reading pixel brightness. Expect roughly ±10% after you calibrate it once
against a known reference; it's meant as a directional signal, not a laboratory instrument.
What are the three scores?
Vitamin D score — how close you are to your daily vitamin D
target (sun + supplements + diet). Circadian score — whether you got bright light
early and dim light late, weighted for its effect on your body clock. OPSIN score —
the overall quality of your light day, combining both plus indoor-light adequacy and your daylight
time from Apple Health.
What is the Vitamin D Balance Sheet?
It's a simple ledger of your day: your target, what you've taken in (sun + supplements),
how much your skin can safely make from the sun today, and the remaining gap. It then routes the gap
honestly — "sun can safely cover ~X IU today; take ~Y IU to close the rest." On low-UV days it tells you sun
alone can't get there, rather than nudging you toward a sunburn.
What's the "estimated vitamin D level," and how do I calibrate it?
OPSIN models your blood 25-hydroxyvitamin D over time from your intake, using standard
pharmacokinetics (vitamin D has a ~15-day half-life in the body). It's a modeled estimate, not a
measurement, shown with a confidence band. When you log a real blood-test result in Settings, OPSIN
anchors and tunes the estimate to you — the more results you log, the tighter it gets. Always confirm your
status with a blood test interpreted by a clinician.
Is the AI coach giving medical advice?
No. The OPSIN Coach is a general wellness assistant grounded in your own data and a curated,
cited knowledge base. It's built with hard rules and an independent safety filter: it never diagnoses, never
prescribes doses to treat a condition, never suggests more than 4,000 IU/day, and never tells you to exceed
your safe sun window. For anything medical — deficiency status, dosing, a condition — it will point you to a
clinician and a blood test.
Safety
Can OPSIN stop me from getting sunburned?
It estimates your time-to-burn for your skin type and current UV, and warns you as
you approach it — but it can't see your actual skin, sweat, sunscreen reapplication, or reflected
UV from snow/water/sand. Always use your own judgment and standard sun protection. If you have a
history of skin cancer or photosensitivity, follow your doctor's advice, not an app.
Should I take vitamin D supplements?
That's a decision for you and your healthcare provider. OPSIN lets you log
supplements so your daily total reflects everything you take, but it does not prescribe doses and
is not medical advice — especially at higher intakes.
Privacy
Who can see my data?
On the iOS app, your health and profile data stays on your device. On the web app,
your data is stored in our secure cloud database under your account so it syncs across devices, and we
use a small set of processors to run the service (sign-in, hosting, UV forecasts, the AI coach, and
privacy-tuned analytics). We don't sell your data. See our
Privacy Policy for the full list.
Does OPSIN use Apple Health?
Only with your permission. It can read things like your time in daylight, sleep
schedule and age to personalize your plan, and write your estimated vitamin D and light-exposure
sessions back to Health. You control this in your device settings.