Night vision simply means that you have the ability to see at night or in a dark environment by using either technological means, biological means or a combination of both. The human has a poor spectral range especially when compared to animals. One out at night it can often take around 40 minutes before you have your “biological night vision”. Our lack of night vision is simple because our eyes lack tapetum lucidum which is a layer of tissue that resides in the eye of many animals either behind the retina or sometimes within. It works by reflecting visible light back through the retina which means there is more light available to the eyes photoreceptors which in the end improves vision in low light conditions.
What is Spectral Range?
Spectral Range is the viewer’s sensitivity to different types of light that would normally be invisible to humans. As humans our vision is confined to a very small sector of the electromagnetic spectrum (otherwise known as visible light). By enhancing spectral range this allows the viewer to “see” otherwise non visible sources the likes of near infrared or ultraviolet light. Many animals have this ability naturally.
There are many animals which have better night vision than humans often due to the biological differences such as the size of their eye which are often larger than humans meaning their lenses are bigger, larger rods in the retinal etc.
We can only compare if we use technology to our advantage. This is done by image intensification or multiplication.
Night Vision Goggles.
Night vision goggles or binoculars work by using a large lens to concentrate the light which intensifies it enabling the user to see better than if they were just using their own vision. Night goggles often have what is known as a large exit pupil of 7 mm or more which means it just gathers available light and focuses it into the user’s eyes. The disadvantage of a large exit pupil however is that many humans cannot take advantage of this because their eyes cannot dilate enough to take advantage of it. To overcome this problem, many of the Special Forces used Atropine drops which made the eyes go into full dilation thus making the effects of the night vision much more effective.
Night glasses are telescopes or binoculars with a large diameter objective. Large lenses can gather and concentrate light, thus intensifying light with purely optical means and enabling the user to see better in the dark than with naked eye alone. Often night glasses also have a fairly large exit pupil of 7 mm or more to let all gathered light into the user’s eye. However, many people can’t take advantage of this because of the limited dilation of the human pupil. To overcome this, soldiers were sometimes issued atropine eye drops to dilate pupils. Before the introduction of image intensifiers, night glasses were the only method of night vision, and thus were widely utilized, especially at sea. Second World War era night glasses usually had a lens diameter of 56 mm or more with magnification of seven or eight. Major drawbacks of night glasses are their large size and weight.
