If you’re anything like me, the concept of night vision has been nothing short of mystifying. It harks back to the cartoonish childhood fantasies of being an invisible superhero that can see through walls. Having regrettably advanced to adulthood, I’ve managed to gather up a fair bit of knowledge on the subject which can help explain how this incredible technology actually works.
Before we dive in, it’s important to understand that night vision’s technical definition is simply the ability to see in low-light conditions. This definition is vague enough where virtually anything can be considered night vision. Something as simple as turning up the brightness in a photo editing program could be “night vision”. Lame, right? Lets move on.
Night vision is accomplished using three different techniques: infrared illumination, thermal imaging, and digital manipulation.
Infrared illumination is a remarkably simple and economical solution to the problem of seeing in the dark. These devices work by using an infrared bulb to emit infrared light which is then reflected back onto a sensor. This sensor then constructs a usable image which can be viewed through a tiny screen. Most organisms on this planet, including humans, are not able to see infrared light (except for some frogs and snakes) which is why this method is so effective. In this picture below, you can see the infrared illuminator mounted on the bottom of the device.
Another way to accomplish night vision is through the process of thermal imaging. Using an extremely sensitive instrument called a bolometer, thermal optics actually use the differences in heat signatures to construct a visualization of their surroundings. Thermal imaging is unique in that it does not depend on reflected light to work. This is why thermal optics have much higher contrast than infrared optics. The downside to thermal imaging is that it’s prohibitively expensive (about 20x more expensive than infrared illumination).
The third form of night vision is an interesting one. It’s equivalent to importing a picture into Adobe Photoshop and turning up the brightness. This process, known as digital manipulation, does not actually illuminate anything and only makes minor adjustments to basic image properties (like brightness or contrast). While it may sound like an underwhelming way to get the job done, it actually works pretty well. Digital manipulation will never be useful in a pitch black environment but it can absolutely help enhance the little light that is available.
Here is a fun fact: virtually all infrared and thermal optics both incorporate digital manipulation to some degree. The important distinction is that it’s not the only thing they use.