Can you explain how Infra red day night cameras work ?

The ability to film in low light conditions or even complete darkness is essential in many CCTV systems. Much criminal activity takes place under cover of darkness and when most of us are sleeping so you can see why it's so important.

Low light filming can be dealt with by careful selection of the CCTV camera electronics. There is a huge difference in the way cameras perform in low light conditions with good quality cctv cameras able to film in conditions the human eye struggles to see in. We spend many hours testing the performance of different electronics before settling on a particular CCD and DSP or Chipset combination. What works well during the day may be less good at night and visa-versa. It is essential to have a camera which performs well across the board.

To film in total darkness and to help low light filming many cameras, known as day night cctv cameras, feature built in infra red or I/R lighting. This is provided by a series of leds mounted at the front of the camera surrounding the lens. Infra red light is invisible to the human eye so they don't shine a beam of light as such but to the CCTV camera which can see infra red light it's like shining a torch.

People are often confused as to just how the day / night cameras in their home CCTV will change between daytime and night time filming. What happens is that as light levels fall the camera's internal electronics detect the drop. When levels fall to a pre-determined point the camera switches from colour to black and white mode. It does this because black and white cameras are more sensitive and so produce a clearer image

Independently from the camera's internal electronics the infra red light source on the camera has a built in photo resistive cadmium cell which switches on the I/R leds as light levels drop. In this way the camera automatically switches between day and night mode. There is no need to manually switch anything.