Been wondering …
If you were to put an animal with excellent night vision into a totally dark room, with a mirror on the wall … would that animal see its own reflection, or would there be no reflection to see because of lack of light? 
Without light the animal wouldn’t be able to see.
Mirrors work by reflecting light back at the viewer, therefore no light = no reflection.
Animals that “see in the dark” don’t. They see in very low level light. Sight requires light. A totally dark room has none. ergo…
“very low level light”
“dark”
Same thing aren’t they?
(I am just being pedantic. Ignore this post)
So what you’re all saying is that however good an animal’s night vision is, there has to be some light for the animal to be able to see? And in the presence of any light at all, there would be a reflection?
OK … what about a human equipped with infra-red vision specs, or whatever - in a completely dark room, would they see anything in the mirror? My guess would be no, even though they would be able to look down and see their own body …
Night vision goggles work the same as animal’s eyes. They enhance the little light that is there. There is no such thing as Night vision goggles that can see with no light. So yes, they would see a reflection.
And I think infra-red viewers would see a reflection too, but I am not 100% sure on that one.
Sorry, I didn’t read your post correctly. You were asking about infra-red googles.
Infra-red is still light. so infra-red goggles would still require the presence of light. Light that our eyes can’t detect, but still light.
Infrared googles require infrared too work. I don’t know whichwavelengths infrared googles can see; if it is the shorter infrared wavelengths you’d be able to see your reflection, but if it is th longer wavelengths you wouldn’t as glass absorbs the longer infrared frequencies (I think it is the former as I’ve seen seen footage shot by infrared cameras on copumentaries and glass is usually opaque).
nope - infra red is not the same as light, if by light you mean the visible spectrum. Infra red is a lot more like heat. A person using such night vision glasses and looking in a mirror, in a room that has NO light in the visible spectrum - i.e. light that be detected by human eyes - would still detect his image in the mirror, because he is, in fact, emitting infra-red radiation. Assuming that infra-red radiation is reflected by a mirror, and I believe it is, what he would “see” in the mirror would be what another person with infra-red goggles would see looking directly at him. Those glasses that enhance the avaliable light in very low light conditions do, in fact, work because there is SOME light. In fact, the total absence of light is almost impossible to find naturally any more. You have to be deep within a building, or in a cave someplace to be in a totally dark room.
Actually, glass mostly reflects longwave IR (some small amount does get absorbed, of course). This is how greenhouses work. Light passes through the glass, heating objects inside. These warm objects re-radiate some of this heat energy as longwave IR, which is reflected back by the glass, further warming the objects.
Wow, you can organize search results by how hot the websites are? That could be useful.
Glass will absorb the longer infrared radiation almost completely; I don’t know how much is re-emitted, but I don’t think you would see a reflection. This also depends on other properties of the mirror.
The bolded part should read something like “slowing down the cooling rate” or something. The way you wrote it it sounds like energy is coming from nowhere.
I thought that glass was transparent to most frequencies of infrared, just like visible light. It’s with ultraviolet that glass suddenly becomes nearly opaque.
Glass is transparent to the higher frequencies of infrared, but not to the lower frequencies.
bolding mine
Ummmm
So in a room lit only by ultraviolet light*, you’d see nothing in a mirror?
- Is this the same as the lights that used to be (still are, for all I know!) used in 70s discos? The ones I used to make sure never to wear a white bra under?
It’s not the same light, but it is quite close.
I’m not sure what was unclear to you, so I’ll elaborate for the science-impaired–though I’m sure you know most of this. Visible light and shortwave infrared pass through glass. This is fairly obvious, hence the usefulness of windows. In a greenhouse, this light hits the plants, the ground, the shelves and anything else inside. Some of it is absorbed, and some of it is reflected away. The light that is absorbed imparts energy to the atoms that make up the plant, the ground, the shelf or whatever. This energy is heat.
If the only “light” in the room was in the UV spectrum and past the visible spectrum, you would see nothing at all. You eyes only see light in the range of 400-700 nanometers or so. So no matter how much IR or UV “light” is in that room, you’d see it as totally dark.
The “blacklight” phenomenon in discos is different. These lamps are emitting light in the ultraviolet range. Some compounds fluoresce in response to UV light, and you see that glow. See here for more info. Black light posters are painted with compounds that fluoresce and look cool under the light. Your white clothes glow because of the detergent you use when you wash them (dark clothes would glow too but the other colors in there absorb most of the radiation).
You see purple/blue coming from a black light because it looks cooler, and it’s also (in the case of UV lamps used in labs) a way to tell that the lamp is ON, because you wouldn’t know otherwise.