Night vision

Night vision is the ability to see when there is very little light, either using our eyes naturally or with special tools called night-vision devices. To see in the dark, we need both the right kind of light and enough light. People don't see very well in the dark compared to animals like cats, dogs, foxes, and rabbits. This is because human eyes lack something called a tapetum lucidum, a special layer behind the eye that helps animals see better in the dark by reflecting light back through the eye.

Types of ranges

Night vision helps us see when there is very little light. Some tools can detect kinds of light that our eyes cannot see, like a special type of light called near-infrared or ultraviolet. Animals like mantis shrimp and trout can see more of these special lights than we can.

Many animals can see better than humans in the dark. They have eyes that are built differently, like bigger pupils or special layers that help their eyes use every bit of light. We can also make tools that help us see better in the dark by using special cameras and sensors.

Biological night vision

Further information: Adaptation (eye) § Accelerating dark adaptation, and Scotopic vision

All eyes have special cells that help us see, and these cells contain molecules that change when they sense light. When it gets dark, our eyes need time to adjust so we can see better. Most of this adjustment happens in the first few minutes of being in the dark.

Some animals, like cats and dogs, can see much better in the dark than humans can. This is because they have a special layer in their eyes called the tapetum lucidum that helps them see by reflecting light back through their eyes. Humans and monkeys do not have this layer, which is why our night vision is not as good.

Night-vision technologies

Night vision technologies can be divided into three main groups: image intensification, active illumination, and thermal imaging. There is also a new kind called digital night vision, which uses very sensitive cameras.

Image intensification makes light brighter. It uses light from stars or the moon and can show images even in very dim light. This is often used in night vision goggles and cameras.

Active illumination adds extra light to help see better. It uses special light that our eyes can't normally see, making images clearer. However, this can sometimes give away a person's location.

Thermal imaging detects heat. It can see in the dark and through fog or smoke by noticing temperature differences. These cameras are used in security and on aircraft, but they cannot see through walls or glass.

Night-vision devices

See articles: Night-vision device and thermal imaging camera

History

Before special technology was invented, people used night glasses to see in the dark, especially on ships. These old night glasses were big and heavy, with large lenses and strong magnification.

Current technology

A night vision device (NVD) is a tool that helps people see in the dark. It is often used by military forces. Now, more people can use night vision technology, even for things like flying planes. For example, enhanced vision systems (EVS) help pilots see better to avoid accidents. These systems are part of new airplane equipment made by companies like Cirrus and Cessna. The US Navy is also using night vision technology in special displays on helmets made by Elbit Systems.

One type of NVD is the night vision goggle (NVG), which has two eyepieces for both eyes. It can use one tube to send the same image to both eyes or a separate tube for each eye. Night vision goggles can also be used with magnifying lenses to make night vision binoculars. There are also smaller devices called monoculars with just one eyepiece, which can be attached to guns as night sights. NVG and EVS technology is becoming more common in helicopters to make flying safer. The NTSB is thinking about recommending EVS as safety equipment.

Night glasses are single or binocular with large lenses that gather and focus light, helping people see better in the dark. They often have a large exit pupil to let more light into the eye. But not everyone can use this well because of how much their pupils can open up. Sometimes, soldiers were given special atropine eye drops to help their pupils open wider.

Today, the PVS-14 monocular is the most popular night vision device used by many military groups. It is known for being affordable and versatile. Some more expensive devices, like the PVS-31 binocular and GPNVG-18, are used by special forces. Monoculars are usually chosen by well-trained military units.

Night vision systems can also be put in cars. An automotive night vision system helps drivers see better in the dark or bad weather. These systems use special cameras, sometimes with extra lighting, to show the driver what is ahead. Some luxury cars now offer these systems as an option.