Why do night vision goggles work in total darkness?

2021-08-12

When it comes to night vision, most of us think that these products enable us to see at night. However, there are different types of night vision technologies, which have different uses and capabilities.

There are three main types: image intensifier night vision, digital night vision devices, and thermal imager. Although there are many differences, they all share common architecture: an optical tube that is customized for imaging infrared light and an integrated infrared sensor that converts invisible infrared light into visible light that can be seen human eye.

We are familiar with the image produced by the intensifier tubes , as we have seen on movies, news, or popular science publications, it is an optic which produces green and black images.  Intensifier tubes use reflected ambient infrared radiation, which is invisible to the human eye, to generate images just like the visible light, this infrared radiation is emitted by the Sun and the stars, and illuminates everything—including the Earth and the Moon. The infrared light that is generated by the stars reflects from the Moon and forms the ambient infrared illumination that is used by night vision devices at night. Intensifier-tube night vision devices convert the infrared light reflected from objects and convert it to visible images. At the heart of these devices are the intensifier tubes, which are constructed of tubes that have a photocathode at one end, an internal anode in the middle, and phosphor screen on the other end.Between the photocathode and the anode there is high-voltage to create a strong electrostatic field. When infrared light strikes the photocathode, electrons are emitted and accelerated by the electric field toward the phosphor screen, which produces a visible image. Since the inception of these devices, their basic principle of operation has remained basically the same; however, resolution, clarity, and image brightness have improved significantly over the years.