I’ve always wondered about IR (Infrared) radiation. Yes, it has longer wavelengths but does carry heat (or what do night goggle glasses see??) Why is it never mentioned? The silver coating on some sunglasses make a nice block (“blocker”) against the IR – I’ve always found them restful.
A separate and maybe minor point: glass (as opposed to plastic, the material of "sunglasses) naturally blocks out much UV light. Even plain glass glasses without that green tinting will block out significant UV. I’d be curious to know how much of the reputedly harmful UV is blocked out by glass.
It’s never mentioned because IR isn’t bad for your eyes where UV is. It doesn’t carry heat… it has energy.
An IR detector sees you emitting IR radiation, not reflecticting it. Any object (people qualify) above absolute zero emits blackbody radiation and in that temperature range it is mostly IR. I believe that most night vision goggles are actually looking at small amounts of light and not infrared.
I’m not really sure what the range of harmful UV is and glass can either be very transparent in the UV or not, depending on what kind of glass youre talking about.
I’m not sure what you mean. Heat, energy… energy, heat. You think there’s a difference?
IR radiation and UV radiation are both electromagnetic radiation. Their frequencies lie on either side of our visible spectrum.
If your eyes are assaulted by bright light, it can hurt: too much heat/energy received. The brain recognizes this when the light is in the visible spectrum. But we don’t “see” the IR or UV. Their heat/energy, though, is added to the visible that we do see.
If you experiment with a prism, you’ll find that energy still comes through at wavelengths too long to see (ie. the IR.) Blocking that extra energy can give the eye relief.
As for glass blocking UV… Years ago, I worked in a field where we made devices to segregate different spectra (used to identify different molecules.) Glass had the characteristic that it naturally blocked out the near UV. If we wanted a device to be able to see UV, we had to use a different substrate. So plain glasses give some protection – at least of near UV, I don’t know about very short wavelength UV. (Another nice feature of plain glass is that it will cut down the light coming through by about 8%. So between the light reduction and the UV protection, plain glass has some helpful qualities.)