Infrared illumination lights a scene with light the eye cannot see but the camera sensor can. Most cameras switch to it at dusk by removing the IR-cut filter. Range depends on the illuminator, the lens and the scene, so a datasheet distance is rarely the distance that produces usable detail.
IR is why a camera can appear to see in total darkness. It is really adding light, and it flattens the scene into monochrome.
Shorter and longer wavelengths
Shorter-wavelength emitters are more efficient and cast a faint red glow visible to people. Longer-wavelength emitters are less visible and generally carry less distance.
Overexposure at close range
An illuminator built for a long throw will blast a subject standing at the camera. Smart IR reduces output as the object approaches; check the minimum working distance.