The context of this page is Infrared Illumination for Night Vision. Infrared is used in night vision equipment when there is insufficient visible light for human eyes to see. Night vision devices such as cameras fitted with Infrared vision capabilities operate through a process involving the conversion of Infrared into images that can be seen by human eyes such as on a video screen or on paper. Infrared light sources can be used to increase in-the-dark visibility without using a visible light source.
An Infrared Illuminator throws out a beam of infra-red light that is invisible to the naked eye but visible to a Night Vision Device. It is similar in function to a flashlight and the distance the Infrared emitted has a limit. A powerful eye-safe illuminator allows the coverage up to 100 metres with a certain degree of beam angle. The illumination is classified as Active Infrared.
This picture(Left) was copied from Wikipedia.
Active-infrared night vision: the camera illuminates the scene at infrared wavelengths invisible to the human eye. Despite a dark back-lit scene, active-infrared night vision delivers identifying details, as seen on the display monitor.