Straight answers to common questions about sunlight, UV, and vitamin D.
What dminder did well, what its 2026 rewrite broke, and what to look for in a free vitamin D and sun-session app that replaces it.
Dawn-simulation lamps make waking easier in trials, but a bedside lamp is a few hundred lux. Your clock is set by the 10,000-plus lux outside, once you are up.
The official UV forecast is a clear-sky number cut by one forecast cloud factor. Real clouds pass most UV, so an overcast day is not UV 0.
Outdoor light within an hour of waking, a fixed wake time, and dim evenings move the clock about an hour a day. A seven-day protocol with times.
Sun on skin makes D3 plus sulfated D, nitric oxide and beta-endorphin; a capsule covers one pathway. When to use each, and how to dose from a 25(OH)D test.
Sun times, UVA rise, the UVB window and a cloudless ceiling can be computed on the phone. The live UV number needs cloud and ozone data and a connection.
Most UV apps show a forecast for a grid point, not a reading where you stand. Low sun, clouds, stale hours and coarse location all produce a 0 in full sun.
Brown and black skin (Fitzpatrick V and VI) needs three to eight times the UVB dose of fair skin. Minutes to 1,000 IU by UV index, and what to do in winter.
No. Window glass absorbs almost all UVB, the only band that makes vitamin D. What passes through is infrared and UVA, and what you need is open sky.
No UV index is safe on its own. Burn risk is the index times minutes on your skin type. Burn times by Fitzpatrick type at UV 3, 6 and 9, and what 3+ means.
UVA does not arrive at sunrise. It rises once the sun clears roughly 10 degrees, about 50 to 100 minutes after sunrise depending on season and latitude.
Three outings: within an hour of waking for your clock, midday for vitamin D, late afternoon to wind down. The minutes for each and how they move by season.
Every UV app shows a model of the index, not a measurement. They differ on data source, clouds, update cadence, location resolution, ozone, and peak vs now.