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I know you don't get a tan through a glass window. But I don't know whether tanning and vitamin D are produced using identical wavelengths. So my questions are :
-Do you synthesise vitamin D through a window
-Does indirect sunlight reflected from the walls and furniture of a sun lit room trigger vitamin D production ?
The sunlight through the window does not stimulate vitamin D synthesis in the skin.
Sunlight and Vitamin D (PubMed):
Since glass absorbs all UVB radiation, exposure of the skin to sunlight that passes through glass, plexiglass, and plastic will not result in any production of vitamin D3 in the skin.
The sunlight reflected from the surfaces, especially snow, can contribute to vitamin D synthesis in the skin.
Vitamin D status and sun exposure in India (PubMed):
The geophysical parameters like...surface albedo (the fraction of light reflected from earth’s surface)...affect vitamin D3 production in the human body.
This process becomes significant if surface albedo is high, e.g. if covered with fresh snow (albedo ~90%)...With the exception of snow, most natural surfaces have a low albedo in the UV, of the order 5% for vegetation, 10% for soils and rocks, and up to 20% for dry sand, the same as some concretes and cement...
and (Research Gate)
3-5% for water
To produce Vitamin D you need to get radiated by light with wavelengths below 300 nm. So let's look at the reflectance and transmittance of the materials.
A window made of glass has a transmittance of nearly 0 % for UV-Radiation. https://physics.stackexchange.com/questions/74638/transmittance-of-glass
The reflection depends on the surrounding. Asphalt for example has a reflectance below 5 % whereas the value for snow is close to 100 %.
In general I would assume that reflected light on the northern hemisphere under daily circumstances is not enough for sufficient production of Vitamin D. If you live on a high mountain this might vary.
