I’ve always “known” that window glass filters UV radiation from sunlight. You can’t get a sunburn through a window, right?
Peace,
mangeorge
You sure can. Some glass is treated to block UV light, but glass isn’t filtering UV by default.
Just as sunglasses never filtered UV light prior to special coatings that filter UVA and UVB.
UVA rays will pass through glass, but the more harmful UVB rays are blocked. I think you could probably still get sunburned through a window pane in intense sunlight, but as with other sunscreens it would take much longer.
I wear eyeglasses with “Transitions”, which react (get darker) to UV light. They do not noticeably darken in a vehicle. I have also gotten a mild sunburn on a very long summer trip with the windows up and the a/c on.
UV light will also fade furniture and drapes and such after long exposures.
Bottled beer in green or clear glass tends to skunk more quickly than beer in brown bottles.
My recollection and anecdotal experience says that Telperion is on the mark. It naturally blocks some UV light…but not all of it.
A complete answer depends on the exact type of glass and its thickness.
“Vanilla” glass is fairly opaque to the UV-B band, which is usually considered to be the most damaging to your skin. At typical window thickness, it will block around 90%+ of UV-B. It’s still mostly transparent to UV-A, though, which isn’t entirely harmless to your skin.
Automotive glass is a special case, though. Because it is “safety glass”, it also contains a layer of a plastic called polyvinyl butyral, which – as I understand it – results in a window that blocks something like 97-99% of both UV-A and UV-B. If I recall correctly, that’s roughly equivalent (in terms of UV-B blocking, anyway) to wearing SPF 50 sunscreen. Additionally, except for a period just after sunrise and just before sundown, you usually don’t get full sun exposure while in a car to begin with. So unless you have very fair skin and are out for a very long drive, I think it’s unlikely that you could get a sunburn while driving around.
The Master speaks:
" *To summarize briefly: some ultraviolet rays can pass through car window glass, although most of the burning (as opposed to tanning) rays can’t. On the other hand, most sunlamps aren’t made of ordinary glass–they’re made of quartz or special UV-transparent glass.
Having thus confronted our ignorance, let us humbly endeavor to learn. Ultraviolet light, which causes both erythema (sunburn) and tanning, ranges in wavelength from 4,000 angstrom units (A) down to about 100 A. (Light with wavelength greater than 4,000 A lies in the visible spectrum.) The most potent rays for burning and tanning lie in the 2,900-3,050-A range, with radiation of 2,967 A supposedly being most effective of all.
Ordinary window glass, however, is pretty much opaque to wavelengths below 3,000 A. From this we deduce that the intervention of a window will significantly reduce but not halt the burning/tanning process.
In addition, UV rays above 3,200 A will cause tanning (but usually not burning) if administered in sufficiently massive doses, such as you get when you’re driving across the desert.
I understant that it’s the IR radiation in sunlight that warms you? And glass is transparent to IR?
I just noticed that my left arm is no longer darker than my right! For the last few years I’ve always driven with my windows up.
Glass is not transparent to IR.
At least, it’s less transparent than it is for visible light. This is what causes the greenhouse effect in an actual greenhouse: Any kind of light at all (including the visible light that passes through glass easily) can warm an object, but the light produced by a warm object depends on its temperature, and for most reasonable Earthly temperatures, the light so produced is infrared. So the energy ends up trapped in the greenhouse, and it stays warmer than the outside.
I suspect it also has a lot to do with the fact that a greenhouse is on the ground which is warm itself. Glass is pretty darn good at blocking IR though. I don’t know about near IR, but for mid IR glass is transparent the same way a brick is. Barring symmetry rules, any covalent bond absorbs in this region pretty strongly. You certainly cannot take an IR spectrum through glass.
Stand back, I’m going to try science! 
I went out on my balcony and played around with several remote controls (for my TV, satellite receiver, and sound system), and none of them had any trouble controlling their respective devices through the balcony window. I was at a distance of about 15 feet or so from the equipment. I also tried bouncing the signal off a mirror (which would have to pass through the thickness of the glass twice), and through a large glass jar, neither of which seemed to present any obstacle.
Not a very rigorous experiment, to be sure, but I would hazard to say that the glass used in residential windows, mirrors, and jars is fairly transparent to near-IR.
But IIRC, the IR LEDs used in TV remotes are very near IR, so these results aren’t that surprising given that glass doesn’t block visible red light, either.
True. You can even see the light from a remote with a digital camera, but it turns up blue because of the built-in filter.
As usual, it depends. What window glass are we talking about? Most modern house window glass now comes standard with what is usually refered to as Low-E.
This is a thin metalic coating that helps prevent UV from entering the house and warming it. It also helps reduce radiant energy from escaping when it’s cold outside. There are various levels.
The windshield is made like this, true, but the side and rear windows are not; they are ordinary tempered glass, no plastic coating involved.
I’ve done more rigorous experiments. The glass blocks a bit more than you think.
I had to find a way to enclose an IR receiver so that it could survive outside in a power plant. I was hoping that we could use the standard glass that came with the enclosure we were purchasing. Unfortunately, when I made measurements, the glass was blocking about 45 to 50 percent of the signal. Your TV remote will still work, but the range will be reduced somewhat. Because of the reduced range I was forced to replace the glass with IR transparent lexan.
I posted a question related to that some time back and although IR does heat you up, plain ol’ visible light does too.
Not to derail things entirely, but I think greenhouses work more because they block convection currents than because they block radiative heat loss.