Now, for those of you who don't know much about infrared (IR), here's a little bit and some. Most of us see things in a limited spectrum of colors and light. Light has wavelengths like sound and when it bounces off of something, our eyes will pick it up and interpret it as a certain color..based on wavelength. The same way short sound waves are higher pitched and broader ones are lower pitched, color changes with light wavelength. Here's the visible spectrum of light/colors, simplified:
Taking a look, you may notice the utmost left is red and the utmost right is violet. Beyond what we can see past violet lies ultraviolet (UV). Waves in this territory are a radiation that could even harm us and damage our skin. When you hear about UV rays, it's usually in the case of the sun emitting them and how you can get burned by them, especially on a bright and hot day. On the other side of the spectrum, beyond red...is infrared. Like UV, waves in this territory are a form of invisible radiation. Remember even visible light is radiation, though it's not usually harmful in most cases. There are many kinds of radiation, some that can melt your skin off or poison you or even kill you, other kinds that are harmless.
Even though we cannot see infrared or UV with the naked eye, we can use special equipment to 'translate' the invisible into visible colors. This is what infrared cameras do. You can buy special lenses to put on normal cameras, or you can have the whole camera made stricly for the purpose of seeing IR alone. There are also different ways the IR can be translated. Some high tech IR cams translate the source into something called thermography. Since heat and IR share a lot of the same territory, people can see temperature differences in thermographic pictures. Here are some examples:
Red is the most hot, yellow is next in line, greens follow, and blues are the coldest.
At nighttime or in darkness we find things hard to see. Naturally this makes sense since there's very little or no light to bounce colors back to us. Since IR is beyond normal sight anyhow, info can be picked up and converted into a usually greenish display in nightvision cameras/goggles/hunting scopes etc. Below is an example of nightvision.
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