Infrared light is described as light that is invisible to the naked eye. It has a much longer wavelength that normal light and also a lower frequency as well. Infrared detects how much heat energy is emitting from a person or an object, since all things transfer some kind of infrared light as some point depending on its temperature.
Infrared security cameras use infrared LED (light-emitting diode) lights located on the outside of the camera lens, this is so that the light can capture the images even areas with little to no visible light. The infrared measures the heat emitted from objects in the focus range of the camera.
Infrared security cameras are not day/night cameras and should not be confused with them. A day/night camera does not use infrared light technology and can only give a quality picture if the image to be captured has a consistent source of light. Infrared security cameras will produce a color picture, when visible light is available, as the light diminishes the security camera would automatically switch to infrared light mode, which would transmit as a black and white image.
Quality infrared cameras will have 0.0 lux. Lux is the amount of light that would be required to a good, quality picture, this means that the lower the lux, the lower amount of light required to take a good quality picture. Therefore an infrared security camera with 0.0 lux, translates to a camera that can take quality images in complete and total darkness, with no visible light present at all.
The quantity of infrared LED lights present on the camera will determine how far into complete darkness the camera can see. In some cases cameras are able to see up to 150 feet in total darkness, however infrared cameras are available in long and short range lens and are suited for indoor and outdoor use.