It's common for humans to get lost in a fantasy of having night vision and wish we could navigate a dark terrain stealthily. Other animals can see in the dark, so why can't we?
Unfortunately, our vision consists of a much narrower spectrum of light than many other members of the animal kingdom. In fact, humans are only able to see certain types of light, which means we can't see the light that is present in a dark environment.
Curious to learn more about why we can't see in the dark? Let's take a closer look at how the human eye works, what its limits are, and how humans have used technology to expand the range of light that we're able to see.
Limitations of a Human Eye
The human eye is an immensely powerful organ for perceiving the external world — but it's not without its limits.
Light is processed in the retina of our eyes by photoreceptors known as cones. Each cone cell is capable of absorbing specific types of light — for example, there are red cone cells, blue cone cells, and green cone cells.
The different cones handle different wavelengths along the light spectrum. This means that we can only see a specific wavelength of light if we have the corresponding cone cell in our retinas to process that wavelength.
Cone cells work best in bright light conditions, but we also have another type of cell, rod cells, in our retinas, which are able to detect light in darker conditions.
However, our cone cells will not be able to detect any light in extremely dark environments. However, that doesn't mean there is no light in the space. Instead, it means that the limited light falls outside the spectrum that is visible to us.
Our Visible Spectrum Range
The full spectrum of electromagnetic light is much broader than that which humans are able to see. The electromagnetic spectrum is divided into wavelengths. Light that is visible to the human eye sits roughly in the wavelength range of 380-760 nanometers.
However, visible spectrum range varies depending on the person. For example, some people who possess a condition known as aphakia are able to see light on the ultraviolet spectrum, while most people are unable to do this.
Aphakia exists as a result of the lack of a lens around the outside of the eye since the lens of an eye usually filters ultraviolet light.
What Animals Have Infrared Vision?
Some animals have a visible light spectral range that is much wider than that of humans. Here are just a few examples.
Fish such as salmon, piranha, and goldfish, have infrared vision, allowing them to see in the dark. These fish have an enzyme that activates infrared vision to help them hunt prey and navigate in low light conditions.
Bullfrogs have infrared vision to help them adapt their sight to their environment, whether they're traveling through the reeds above water or swimming through murky low-light conditions underwater.
Some snakes like pythons and rattlesnakes have special protein channels which activate when they detect the presence of heat from their prey. This then activates infrared vision in the snake, letting it track down and eat its prey in low light conditions.
What Can Help Us See in the Dark?
Although we lack infrared vision, humans have come up with ways to see in the dark. Here's how you can enhance your night vision.
Night Vision Goggles
Even in low light conditions, there is still a persistent level of light in your surroundings, although it may not be enough for the human eye to register.
Night vision goggles use a type of technology known as image enhancement. Image enhancement collects up all the low light within view and amplifies it.
The result is that objects which first appeared dark now seem much brighter — bright enough for the human eye to detect and for you to see more clearly.
Thermal Imaging Devices
Thermal imaging devices use a different type of technology than night vision goggles. Rather than using light, they use heat to generate images.
Objects in your surroundings — like people, walls, buildings, electrical appliances, and so on, generate heat. Thermal imaging cameras identify the heat in your surroundings and map them to their location to produce an image.
The results don't offer you color vision, as the color profile offered by thermal imaging relates to how hot objects are rather than their actual color. However, it does define the edges of different objects and shapes, so you can navigate around them in low light conditions.
If no other technology is available to us, the handy flashlight may still be able to help us see in low light conditions.
Simply shining a bright light on specific objects allows light photons to bounce off those objects and enter our retinas, mimicking our experience of seeing them in daylight. It's not the one to go for if you're on an undercover operation, however!
Unfortunately, superhumans who can move rapidly in the dark with infrared vision remain fictional. Our eyes are not the same as other animals since cones restrict our visible spectrum range when there's limited light.
However, it is still possible to enhance your night vision with innovative technology like goggles, thermal monocular, and of course, flashlights. We recommend experimenting with both thermal imaging and night vision goggles to test out both experiences. And, of course, you'll always have a flashlight as a backup!