Humans as a species have very poor night vision, especially compared to other mammals. The eyes can only process a small portion of the electromagnetic spectrum, which is the measurement of all electromagnetic radiation. To put it simply, human eyes can only see a very small percentage (called visible light) of what is actually going on all around them. Cameras have the ability to open up and expose to more of the electromagnetic spectrum than human eyes can process. This feature allows cameras to be used a night, in conditions of low to no light. The camera uses a series of filters to go from recording only visible light (so the images taken look like what people see) to a wider range on the spectrum. This is normally accompanied by the photo or video having a green hue, as the camera is recording more light than humans can see.
Intensity Range
Another simpler way that some cameras record in night vision is to enhance their intensity range. This means that the cameras are enhancing the quality of available light through a variety of processes. Camera features like using an image intensifier, which captures light for longer periods of time than normal, gain multiplication, which changes the way images are exposed. The use of highly sensitive photo detectors all enable cameras to expose proper looking images under conditions of low light.
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