Active illumination couples imaging intensification technology with an active source of illumination in the near infrared (NIR) or shortwave infrared (SWIR) band.
Thermal imaging optics detects the temperature difference between the background and the foreground objects and are excellent tools for night vision. They detect thermal radiation and do not need a source of illumination. They produce an image in the darkest of nights and can see through light fog, rain and smoke (to a certain extent). Thermal imaging make small temperature differences visible.