Night vision is the ability to see in low-light conditions. Night vision technologies can be broadly divided into three main categories: Image Intensification, Active Illumination, and Thermal Imaging.
This magnifies the number of received photons from various natural sources such as starlight or moonlight. Examples of such technologies include night glasses and low light cameras.
Active illumination couples imaging intensification technology with an active source of illumination in the near infrared (NIR) or shortwave infrared (SWIR) band.
Thermal imaging detects the temperature difference between the background and the foreground objects. Thermal imaging cameras 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 cameras make small temperature differences visible.
Night Vision and other lowlight cameras are not very useful during twilight hours when there is too much light for them to work effectively, but not enough light for you to see with the naked eye. Thermal cameras aren’t affected by visible light, so they can give you clear pictures even when you are looking into the setting sun. In fact, you can aim a spotlight at a FLIR and still get a perfect picture.