A common feature in security cameras is night vision. Your average video camera would show nothing but pitch black if left recording a moonlit night scene. Since it’s rather important that security cameras can see what’s going on at all times of day, extra hardware is put in to give these cameras the ability to see at night. This article will explain how night vision in security cameras works, and will describe why not all night vision is equal.
How Night Vision Works
There are a few different kinds of night vision. One that is often thought of is used in night vision goggles to allow humans to see. This isn’t how the night vision technology used in security cameras works.
Cameras are capable of seeing a much bigger spectrum of light than humans are. We can see the color spectrum, red to violet, and wavelengths longer and shorter than that don’t affect our vision in a useful way. Video cameras, however, are capable of recording these wavelengths because they’re not limited by biology. You might wonder how we as humans would even be able to see these wavelengths, even if they were recorded. What color would they look like?
They wouldn’t have a color, our eye still wouldn’t be able to process them. In fact, recording wavelengths outside the color spectrum onto a digital image even distorts the colors we can see. Recording infrared, for instance, makes visible reds look fuzzy and out of focus. So, as a workaround, security cameras recording infrared get rid of color entirely and just show the image in black and white. Wavelengths are now being represented as how much light is entering the camera, rather than how much light and of what color. Now including infrared no longer distorts the image. This is why nighttime security camera footage is monochrome.
Why include infrared light in security camera footage to begin with? Since there isn’t enough visible light at night, security cameras need to find light from somewhere. One alternative solution would be to surround your house with floodlights. Security cameras wouldn’t need night vision then, there’s lots of light out. However, that’s not very sneaky, and having lights blasting at night is neither desirable nor practical.
Interestingly enough, night vision security cameras do just that. The security camera blasts light out in the direction they’re facing, and use this ample light to record an image. The difference is that security cameras are emitting infrared light, so it appears to the human eye that no light is shining whatsoever. Infrared light bounces back toward the camera, and the camera records the scene in black and white. Oftentimes, you can see the infrared LEDs (commonly abbreviated to IR LEDs) that the camera uses for night vision surrounding the camera lens.
Black and White vs. Green Images
You may be wondering why images of night vision are are green. That’s because the human eye is more sensitive to green light. Phosphors in night-vision goggles take a black and white image and turn it green so humans can see the image better.
Night Vision Improvements
Some security cameras have better night vision than others. Most often, this means being able to see farther into the night. Security camera night vision can be as low as 10 feet or as distant at 60 feet plus. This sizeable difference in night vision range is mostly dependent on how many infrared LEDs are used, how intense they are, and the image sensor’s performance in low light situations. Be sure to find out the security camera’s night vision range before you buy.
Some cameras reduce the frame rate from the usual 30 frames per second down to 15 or some other lower number. This results in choppy-looking footage, but is a cheap way to improve a camera’s night vision. Bigger image sensors will give security cameras a night vision advantage too, because they naturally let in more light than smaller sensors.
Many night vision security cameras come equipped with an infrared cut-off filter and a light sensor. The light sensor checks how much light is entering the camera, and is used to detect when there’s enough daylight to exit night vision mode or when enough house lights have been turned on. The IR cut-off filter is used to remove the negative effects infrared has on the scene by targeting those specific wavelengths and preventing them from being recorded. The light sensor thus decides when to take the IR cut-off filter on or off. When there’s enough daylight, the cut-off filter goes on because the image ought to be recorded in color, and no one wants those fuzzy reds. When the sun sets, the cut-off filter is removed so that the camera can rely on it’s own infrared lights to record an image.
Night vision for security cameras is a must have, and thankfully, most are equipped with it! Make sure that the security camera you’re looking at has a sufficient night vision range, and comes with an IR cut-off filter to remove the color distortion infrared has during the daytime.