Why is night vision green?
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Eli5 answer: because we see and can differentiate shades of green than any other color. So they use that to display more details in the image. If they just made things brighter it’d get blown out like turning up the contrast and brightness in Photoshop.
Simply put when we ramp from black to red, black to green, and black to blue, and if we time each of these, we see green earlier than other colors. Meaning that our eyes are more sensitive to green wavelengths than others.
Engineers take advantage of this and use a green display on night vision goggles so that we can pick up on those very tiny changes in light intensity.
Contrary to popular belief, it has nothing to do with the number of green-sensitive receptors in our retinas. In fact red-sensitive receptors out number all others. It’s a more complex question of receptor ratio and sensitivity.
There’s a few different ways to amplify light, to massively oversimplify nvgs convert incoming light into electrons, amplify that, and then the electron strikes a phosphor screen that converts it back into light, and the screen only produces green light. You could get different colors with different phosphor screens or using different methods of light amplifcation.
The original night vision / image intensifiers use something like an old TV tube.
It’s called a photo-multiplier, and it’s different to a lot of home CCTV stuff.
The cheaper night vision has an Infra red light source, and a camera that picks up infra red.
It’s almost a bit of a cheat, as it’s like having a floodlight on that a person can’t see.
The decent night vision doesn’t use any hidden lights, it just amplifies the very small amount of light available.
This is projected onto the equivalent of a tiny TV screen.
This is a tube with a thin layer of phosphorus on it, and that glows green.
It’s the same green like very old computer screens, oscilloscopes etc, the most basic form of a TV screen will be green.
Others have answered the question, but note that white night vision devices are produced as well. It’s more of a white with a slight blue hue, but it’s not nearly as green as the traditional tubes.
Honestly, after just a minute of using it, you don’t really notice the color either way.
So ELI5 (wildly oversimplified, and slightly incorrect) version: most night vision uses green phosphorus. This means that the image displayed is green tinted. There are white phosphorus goggles that display an image that is black/white. Essentially the type of chemical used in the physical components of the goggle tint the resulting image.
The reason night vision images appear green is because the devices use a phosphor screen to convert the electrons into visible light. Phosphors emit light when excited by electrons. Green phosphors are used because our eyes are more sensitive to shades of green, thanks to the way our rods and cones are structured. Green light appears brighter to us in low-light conditions compared to other colors.
So, when the electrons are converted back into visible light by the phosphor screen, they emit a greenish glow, making the image appear green in night vision devices.
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