The ability to film in low light conditions or even complete darkness is essential for many CCTV applications. Part of the that ability is down to using the right electronics, the other element is whether a camera is fitted with infra red or IR lighting.
Infra red light isn't visible to the human eye but CCTV cameras can be designed to see light in the IR spectrum. This means that to the camera its like shining a torch. When light levels fall the camera automatically switches to black and white and providing it is fitted the IR illumination switches on.
Previously cameras had separate infra red light lamps bolted onto the side of their housings. It made the whole unit very large and industrial looking. In more recent times cameras have been designed with IR lighting built into them. This greatly reduces their overall size and visual impact. It also reduces cost when compared to modular cameras using separate lighting units.
Many people selling CCTV cameras describe them in terms of TVL (television lines), and infra red "range". Do not confuse this with the optical range of the camera ie. the distance at which a camera can record detail. That is determined by the lens. The IR range is a largely immaterial figure, often made up and is supposed to represent the distance at which the camera's infra red can be detected. We deal with this topic in our camera buying guide .
Ultimately how well the camera uses that IR light will be determined by the electronics. The distance at which detail can be captured will be decided by the lens. The wider the angle of view the shorter the distance at which detail can be recorded.
It is worth keeping in mind that IR light has to bounce back off a surface for the camera to be able to see anything. Just pointing the IR into space will result in a black screen.