Operation of CCTV from the camera as the video receiver to pick up the image, it must have a light shines onto the object and light would affect the object then reflects back out.
From the work of the CCTV camera is the input. You get the picture, it must have a light to the object and the light is incident on the object. And then return to the
The work of CCTV started from the camera as the image signal receiving. To get the image must be the light to the desired object and the light that hits the object. Then reflected back out.