How do night vision work?

Are you curious about how night vision devices let you see objects in the dark? Night vision devices are devices that use physical and electronic technology to amplify weak light, and they can let you see a green or black and white image. The working principle of night vision devices is actually not complicated, they are mainly composed of the following parts:

Objective lens: This is the front end of the night vision device, its function is to collect the weak light in the environment, such as moonlight or starlight, and focus it on a small point. The size and shape of the objective lens determine the field of view and magnification of the night vision device.

Photoelectric converter: This is the core of the night vision device, its function is to convert the collected weak light into an electronic signal, and amplify it by hundreds or thousands of times. The type and quality of the photoelectric converter determine the performance and generation of the night vision device.

Fluorescent screen: This is the back end of the night vision device, its function is to convert the amplified electronic signal back into visible light, and display it on a small screen. The color and brightness of the fluorescent screen determine the image quality and mode of the night vision device.

According to different generations of night vision devices, photoelectric converters have different types and working modes, here are some common photoelectric converters:

Photomultiplier tube: This is the photoelectric converter used by first-generation night vision devices, it is a vacuum tube, inside which there is a cathode and an anode, as well as a series of metal plates called dynodes. When weak light enters the photomultiplier tube from the objective lens, it hits the cathode, causing it to release some electrons. These electrons are accelerated and hit the first dynode, causing it to release more electrons. These electrons are then accelerated and hit the second dynode, causing it to release more and more electrons. This repeats until the last dynode releases hundreds or thousands of times more electrons. These electrons are finally collected on the anode and output as an amplified electronic signal.

Microchannel plate: This is the photoelectric converter used by second-generation night vision devices, it is a thin glass plate, inside which there are millions of tiny holes with a diameter of less than one millimeter. When weak light enters the microchannel plate from the objective lens, it hits the entrance of the hole, causing it to release some electrons. These electrons are accelerated and move along the hole, while colliding with the hole wall, causing it to release more electrons. This repeats until the exit of the hole releases thousands or tens of thousands of times more electrons. These electrons are finally collected on a metal plate and output as an amplified electronic signal.

Low-light enhancer: This is the photoelectric converter used by third-generation and fourth-generation night vision devices, it is a semiconductor device, inside which there is a layer structure called a photocathode. When weak light enters the low-light enhancer from the objective lens, it hits the photocathode, causing it to release some electrons. These electrons are accelerated and pass through a device called an electron converter (ECC), which can convert electrons into photons of different wavelengths, and amplify them by tens of thousands or hundreds of thousands of times. These photons are finally collected on a device called a photodiode and output as an amplified electronic signal.

Back to blog