I realise this is likely to have been answered before, but I couldn’t see it when I searched.
Anyway, is it true that you tan less if the sun is shining through glass? That is, does common window glass block some wavelengths of UV light or something like that? A friend suggested this was the case, but didn’t have any evidence when asked.
Yes, window glass block the vast majority of shortwave UV-B and UV-C, which causes the most tanning (and skin damage), while passing most of the longer wavelength UV-A, which gives very little tanning results.
Too easy! Thanks, guys.
The eight people locked inside Biosphere 2 were quite pasty after spending two years inside due to the UV blocking of the 1/2" glass. An unfortunate side effect was that bees did very poorly as pollinators as they were probably unable to identify UV images of flowers.