The Light Spectrum

We can see the world around us because objects reflect light that our eyes can see and interpret as images. Light is electromagnetic radiation ranging from ultra-violet to the far infrared. The human eye only sees a portion of the full light spectrum, from about 400nm to 700nm.

Infrared Light

At night or in other low light conditions 400-700nm light is lacking. Although humans cannot see infrared light beyond 700nm wavelength, camera sensors can.  Adding 850nm infrared light to a scene significantly improves the cameras performance in low light. Think of it as a flash-light for cameras.