How do night vision goggles work?

If you eat enough carrots, you will be able to see in the dark. Unfortunately, this is not a true fact, but night vision goggles are very much a reality. These goggles, as you might be familiar from military movies and spy thrillers, allow users to see in near-total darkness. But how exactly do they work? These high-tech devices amplify available light, allowing humans to see in conditions where they'd normally be blind. Through the work of several scientists and engineers in the 1920s and 1930s, night vision goggles have become practical and commercially used.

The technology behind night vision goggles

Night vision goggles typically rely on two main technologies: image intensification and thermal imaging. 

• Image Intensification

Image intensification is the most common and involves gathering even the smallest amounts of ambient light — from the moon, stars, or distant streetlights — and amplifying it thousands of times. This process occurs in a tiny photocathode, which turns incoming photons (light particles) into electrons. The electrons are then accelerated through a microchannel plate and onto a phosphor screen, creating a bright, greenish image that users can see.

• Thermal Imaging

Thermal imaging, on the other hand, detects heat rather than light. This is useful when there is no light source, such as in caves or heavy fog. All objects emit infrared radiation (heat), even if cold to the touch. A thermal imaging system detects the temperature differences between objects and translates them into a visible image, showing warm objects in lighter shades and cooler ones in darker shades.

Why does everything look green through the goggles?

Even at night, the photons that reach the lens of night vision goggles contain light of all colors. However, once this light is converted into electrons, the color information is lost. The incoming colored light is transformed into black and white. This begs the question: why do night vision goggles not simply display in black and white? The screens in these goggles are intentionally designed to produce green images, because our eyes are more sensitive to green light. Additionally, green screens are more comfortable to observe for extended periods compared to black and white ones. As a result, night vision goggles have their distinctive and eerie green glow.

Conclusion

These goggles were originally designed for military use, but they are now utilized for various applications, including wildlife observation and security. They provide an enhanced ability to see in low-light conditions, thanks to an innovative combination of physics, electronics, and engineering.

Works Cited

Woodford, C. (2007). How does night vision work? [online] Explain that Stuff. Available at: https://www.explainthatstuff.com/hownightvisionworks.html [Accessed 4 Nov. 2024].