Night Vision helps humans see in what we call the dark. Humans see in only a small part of the light spectrum. Light is made of waves of energy and the longer the wave is, the less energy it has. The shorter a wave is, the more energy it contains which means that the visible light we see has a range of energy levels. Red is the lowest. Violet has the highest energy. The colour spectrum increases in energy as you go from red, orange, yellow, green, blue, indigo, and the highest violet. Below the visible red waves, we can see are even lower energy waves called infrared. We can also call these heat waves. The infrared part of the light spectrum can be divided into three types. Near infrared is closest to visible red light. Mid infrared waves are longer and farther away from visible red light. Thermal infrared has longer wavelengths still. Violet is the highest visible wavelength, which humans can see. Above the violet coloured waves, we see in the visible light spectrum, are the ultra violet waves, which has higher energy waves than visible violet light.

Night vision devices can help you see a great distance away on a cloudy night when there is no moon light and it works in two ways.

One way uses light that that we cannot see toward the infrared end of the light spectrum. This light is amplified to the point where we can see images.

A lens focuses visible and infrared light into a special electronic tube that intensifies a dim image into a strong one. The few photons that exist in the dim light are converted to electrons. The electrons, pushed by a strong voltage within the tube, collide with the sides of the slightly bent tube to create thousands of electrons. Electrons hitting other electrons in the micro channels of the vacuum tube generate thousands more electrons than there were to start with. There is a screen covered with phosphers at the end of the tube. When the electrons hit the phosphers they become excited. A greenish light is given off in the image of what there is to be seen.

Another way night vision is achieved is by using the heat objects give off. This is how thermal imaging works. The light given off by warm objects is focused by a specially designed lens. This infrared light hits an electronic detector device, which creates a detailed pattern of the differences in temperature. This pattern is called a thermogram. The information held in the thermogram is transformed into electrical impulses. A little computer creates usable data from the electrical impulses and the data is processed more and sent to a display where it is seen as various colours, depending on how much infrared light an object was giving off. There must be a temperature difference between objects and their surroundings to detect images. This image can be viewed through a scope like in a pair of binoculars or on a monitor screen.

Michael Russell
Your Independent guide to Night Vision