Twenty pieces

Field Notes

The reference behind the instruments. Each piece explains a mechanism rather than asserting a conclusion, and says plainly where the evidence is contested.

Sun

SunHow Your Skin Actually Makes Vitamin DThe photochemical chain from UVB photon to circulating vitamin D, why the process self-limits, and what that means for how long you should stand in the sun.
SunReading the UV Index Like an Instrument, Not a WarningThe UV index is a measured physical quantity with a precise definition. Understanding what it counts, and what it deliberately ignores, changes how you plan a day outdoors.
SunWhy the Same Ten Minutes Is a Different Dose for Different PeopleThe Fitzpatrick scale, minimal erythemal dose, and how melanin changes both the vitamin D output and the damage cost of identical sun exposure.
SunVitamin D Winter: The Months Sunlight Stops WorkingAbove roughly 37 degrees of latitude, the winter sun cannot produce vitamin D at any exposure duration. The geometry behind that, and what to do about it.
SunDoes Sunscreen Block Vitamin D? The Answer Is Uncomfortably SpecificLaboratory studies say sunscreen should nearly eliminate vitamin D synthesis. Field studies find almost no effect. Both are correct, and the gap between them is where the useful answer lives.

Daylight

Heat

Effort