Minimal erythemal dose — usually shortened to MED — is one of the quiet foundations under Basky’s timer. You will not see a big “MED meter” on the Home screen. You will see minutes. Those minutes are derived, in part, from this idea: how much erythemally weighted ultraviolet would it take to just begin reddening skin of a given type?
Basky treats MED as a ceiling reference, never a target to hit. The product’s identity word is warm. Warm means inviting you outside for a little light — not daring you toward pink shoulders.
MED in plain language
Think of MED as a research yardstick. In photobiology, it is the UV dose (often in joules per square meter of erythemally weighted irradiance) associated with the faintest clear reddening after exposure. It is not a personality score. It is not “how tough you are.” It is a way scientists compare doses across skin types and light sources.
Important honesty:
- Your real-world skin can adapt a little with season and recent sun history. Basky does not try to model every adaptation.
- Illness, medications, and medical conditions can change sensitivity. Basky cannot know those. It is not medical advice.
- A phone camera cannot measure your MED. Basky uses conservative reference values tied to the Fitzpatrick type you choose.
How MED connects to the UV index
The UV index is built from erythemally weighted UV — the same family of weighting that makes MED meaningful. Roughly: higher index means more reddening power per minute. At UV 8, the clock to any given dose runs faster than at UV 3.
Basky’s Exposure Engine combines:
- A MED figure for your Fitzpatrick type
- Today’s live UV (Open-Meteo when location is allowed)
- A target fraction of about 60% of MED
- Guards that clamp the result (no marathon sessions, no nonsense zeros when the sky still has meaning)
The feeling on screen stays simple: “about n minutes of safe sun.” The MED math stays under the hood so the ritual stays gentle.
Why Basky uses ~60%, not 100%
If MED is “just perceptible reddening” in a controlled sense, aiming at the full number would be the opposite of Basky’s promise. The app exists to help you catch just enough to feel good, never enough to burn. Sixty percent is a deliberate buffer — conservative, not macho.
That buffer also supports the anti-shame design:
- Ending the session when the ring fills is success.
- Going past the line caps counted light. There is no bonus for overdoing it.
- Streaks never require you to ignore the window.
MED is not a competition between skin types
Standard tables show lower MED values for types that burn more easily and higher values for types with more constitutive pigment. Basky uses that pattern so fair skin gets shorter windows in the same sky — and deeper skin is not forced into an absurdly tiny timer that ignores melanin’s protection.
What Basky will not do:
- Rank types as better or worse
- Push anyone to “train” toward a darker look
- Frame outdoor time as overdoing the sun or burn-and-repair culture
Your type is a soft input. You can change it in settings if your self-description was off. The Fitzpatrick skin type landing walks through the six types in the same warm voice.
What MED does not cover
MED math for direct sun does not automatically account for:
- Dense shade, umbrellas, or deep porches
- Most window glass (which blocks a large share of UVB)
- Heavy clothing coverage
- Reflection from snow, water, or pale sand (which can add UV)
Basky’s safe-sun window is a starting estimate for the exposure you choose to log. Sunscreen, hats, and shade remain your call — and they are never “cheating.”
MED, vitamin D, and Health
The friendly vitamin D estimate is capped with the same safe dose philosophy. Basky will not invent unlimited D minutes after you should find shade. Optional Apple Health writing is Time in Daylight only — write-only, never a MED or vitamin D medical record.
A calmer takeaway
MED is the science word. Basky’s product word is window. Same backbone, softer surface. When the sky is strong, the window shrinks. When the sky is mild, it lengthens. When the sun is resting, daylight check-ins still count as care for your habit — not as failure.
Now on iPhone. Core free forever. General wellness guidance, not medical advice. More terms live in the glossary; product questions in the FAQ.