All the night vision goggles I’ve looked through makes everything look green… all the movies and games show night vision as green…
Night vision amplifies the tiny amounts of light that’s present… so how come it always turns out as green? Is there something special about green light’s wavelength that makes it act this way? Or is it the filtering process that night vision uses?
The Straight Dope would be appreciated!
The light picked up my night vision goggles isn’t turned green.
The light picked up is displayed on a “mini-moniter” in the headset. The moniter is only capable of displaying the information in green.
I’ll let the more astute members of the TM tell you the exact kind of moniter used.
Your question is comparable to: “Why does my TI-30 calculator turn all the numbers red?”
It is just how the goggles are made.
I don’t have a definitive answer, but I can explain how those devices work. First, the incoming light hits a photocathode, which is a thin sheet of some material which absorbs light and emits electrons. Then the electrons are usually multiplied by a microchannel plate - electrons are accelerated down many microscopic holes, and when they hit the walls, it can knock off more electrons off the walls, which are again accelerated and create even more electrons. Finally the electrons hit a fluorescent screen, which absorbs electrons and emits light. Each hole in the microchannel plate acts like one pixel.
I’m not sure why most fluorescent screens emit green light; I’d guess they are the cheapest, most stable, and/or most efficient fluorescent material available. Anyway, the color of the output has nothing to do with the color of the input light; these are monochrome devices, incapable of distinguishing color.
But why green? Why not black/white? It seems like that’d be a better and cheaper method for a “mini-monitor”. In addition, you’d think that more advanced versions of nightvision goggles would be capable of showing color if it was just a matter of the “mini-monitor”, yet I’ve never seen hide nor hair of anything like that.
I really think that the wavelength for the color green is easier to pick up somehow… I just want to know, what is this property?
I’ve seen green and B&W vision enhancers. The night sight I had on my rifle back in the day showed green, but a night vision sight for a TOW (tube-launched, optical-track, wire guided antitank missle system) launcher was B&W. My WAG (#1) is that it’s cheaper, or was the best technology of the time. If you see those new Cadillac ads, their night-vision stuff is B&W.
Another WAG (#2) is that much like using red flashlights at night to preserve your night vision, using green might allow less of an impact on eyes accustomed to the darkness. Yet another WAG (#3) is that you would want to emit as little white light as possible from the viewfinder, protecting the concealment of the trooper using it. Seeing white light across a valley would be much easier than seeing green.
Make sense?
-sb
Night vision technology was reverse engineered from instruments discovered from the Roswell flying-disc crash. Our minds tend to prefer images that are black & white simply because we are black and white people. They, being little green men, constructed the night vision instruments to produce images in green light. Of course, since we reverse engineered their instruments, our instruments produce the same green light.
Simple, really, when you think about it.
The little monitors in night vision goggles display a green color because they are the same monitors you have on oscilloscopes. The fluorescent screen can only put out green light in the visible spectrum due to the material it is made of. Other factors, such as the preservation of night vision are probably viable factors as well. In this particular respect, the only other color you can really use would be red, which isn’t very nice on the eyes. Remember how green light is supposed to let your eyes relax?
Note: Human vision is most sensitive around yellow. That means exposure to yellow light would make the recovering of night vision the hardest. Green and red are on the two ends of the visible spectrum where human vision is not too sensitive, and that subsequently allows faster recovery of night vision after exposure.
I think that green-emitting phosphors (??sp) are the most efficient, i.e. give the most light for lowest energy. A white-emitting phosphor would need a bigger power supply to enhance the image to the same degree.
Sorry green’s right in the middle.
Does anyone know if color night-vision is on the horizon? Are there color versions available at higher cost or only for use in big-money operations like the military? Is there some technical reason why color can’t be done? (I suspect not)
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I know of at least one device that enables its user to see the complete visible color spectrum in the dark. It’s almost foolproof, handheld, and even has lower power needs than conventional night-vision goggles.
It’s called a…flashlight. 
This whole thing seems pretty simple to me, though I lack the scientific vocabulary to explain it. We see color because unsbsorbed light bounces off of things back into our eyes. In the dark where there is little light we have no real chance of seeing color. All that those night-vision goggles do is enhance existing light and “see” with better eyes than we have. It’s almost a miracle that they work as well as we do - seeing color in the dark (without a MagLight) is just impossible.
No?
I don’t believe that’s correct.
It is true that in dim light, humans can only see black and white. However, I believe that is due to the mechanics of our eyes, that either the rods or cones are more sensative (or something, I don’t have time for details; I’m a big picture man!)
Since in very dim light, the color information is still floating around on those photons, just in more limited number, I suspect that color-night-vision is possible. The question is, is it possible today?
Strictly speaking, the color of objects at night is dependent on what color of light you still have left around. If you use a red flashlight for example, you’re not going to see green and yellow. Now if you happen to use moon light for illumination, then billehunt is correct in that the information is still there, and it’s only our eyes that can’t distinguish it properly.
As for J String…
Tsk tsk, picky picky. If you know how the colors of the visible spectrum are distributed, you should know what I message I am trying to convey. Night vision in blue is bad for the eyes. Perhaps “at the two ends of yellow” would better suit your taste? Now don’t go on about orange please…
The explanation I heard was that the human eye can distinguish more light levels with green light. That is, if one little chunk is just a teeny bit brighter than another little chunk, it’ll be easiest for us to detect that difference if the lighting is all green.
Here’s a link on the subject:
http://policesupply.com/itt-hownvworks.html
If I may tack on my own question to this thread, why is that image intensifiers sometimes have infra-red illuminators? Don’t image intensifiers and infra-red systems work on completely different principles (i.e., light amplification in the first case, and changes in wavelength in the second case)? If visible light amplification is used by the same systems that “translate” (don’t know the real term) infra-red light to visible, how do you tell the difference? I mean, I see blurbs about this kind of thing all the time, and even the technical ones seem to sort of miss the big picture … is it an amplifier or a frequency shifter?
Or maybe II and IR are more closely related in principle than I have thought.
You’re right, light amp and IR do work on different principles, meaning that all the goggles that can use IR do is detect light and, if it’s in the visible spectrum, amplify or, if it’s in IR, shift frequency. The goggles that don’t use IR make use of the amplification system described in earlier posts. IR is used in pitch-black conditions (Think varmint hunting on an overcast night away from big cities.) simply because you can’t amplify what’s not there and IR is a wavelength that most species can’t see (except pit vipers) and doesn’t go through things as readily as UV. BTW, there is nothing especially ‘hot’ about IR. All electromagnetic emissions excite atoms, which is known as heat. If you cranked up a radio transmitter high enough, you’d fry the atmosphere as well as anything else around. It’s how microwave ovens work. (First documented case of this is when the inventor of the microwave oven stood near radar eq. during testing. A chocolate bar melted in his pocket. That’s why old microwave ovens were called radar ranges.)
I haven’t heard of such a system. Current night vision systems work by first converting photons into electrons using a photocathode, so all the color information is lost right there. To get color with such a detector, you have to use three of them with with color filters, feed the output into cameras, combine them electronically and output to a color display. Another way is to use a cooled CCD, which is what astronomers use these days. Cooling systems are heavy and expensive though.
Even with a color detector, you may not get a very clean color image. You know how night vision images are grainy and flicker a lot? Each grain/flash is a single photon being detected. If there are enough photons, the average is stable so the color is stable, but if there are very few photons, the image will be made up of tiny red, green or blue grains/flashes - a huge mess, in other words. There are two ways of getting around this problem: you can collect the light for a long time (many seconds, maybe minutes) and take the average - but at that point the system becomes a camera, not a telescope or goggles. Or you can collect more photons using a larger lens, which makes the system big and heavy.