Can you get vitamin D through a window?

01 / The short answer

A bright room does not mean UVB reaches your skin.

What matters is which radiation passes through the material, not how bright the room looks. The warmth you feel cannot tell you how much vitamin D you are making either.

02 / The detail

Closed glass, an open window and the car.

Opening the window removes that barrier from the direct path of sunlight. Building shade, time, location and the skin actually exposed still matter. Ambient light entering the room is not enough to define the exposure.

The same principle applies inside a closed car: driving time should not be counted as a vitamin D session. Glass types and treatments differ. Blocking UVB also does not establish that a window eliminates all UVA radiation.

You do not need to infer these differences from the colour or thickness of the glass. A simple calculator does not know its optical properties. Taiyo therefore treats “behind glass” conservatively and assigns zero estimated production.

03 / In practice

Zero estimated production is not zero risk.

The tool does not assess UVA damage through a window. Its result describes a limitation of the vitamin D calculation. Keep protection appropriate to your circumstances; warmth and the absence of sunburn do not measure sun damage. WHO ↗

To compare, switch “behind glass” on and off in the calculator while keeping the other values fixed. You can see how the assumption changes the result, without learning your blood levels. If that is your concern, it belongs in a healthcare assessment.