Night-vision

Night vision is the ability to see in low-light conditions. Whether by biological or technological means, night vision is made possible by a combination of two approaches: sufficient spectral range, and sufficient intensity range. Humans have poor night vision compared to many animals, in part because the human eye lacks a tapetum lucidum.

Biological night vision

Biological night vision mechanisms involve the eyes, where the rod cells help in night vision while cone cells in the eyes help in color differentiation. The rhodopsin contained in the rods in the eyes changes shape as it absorbs light. Rhodopsin is the chemical that allows night-vision, and is extremely sensitive to light. Exposed to a spectrum of light, the pigment immediately bleaches, and it takes about 30 minutes to regenerate fully, but most of the adaptation occurs within the first five or ten minutes in the dark.

Technological night vision

Technological night vision is achieved through the use of two major types of technologies: image enhancement (active) and thermal imaging (passive). Image enhancement systems collect tiny amounts of light and amplify them to the point where one can easily observe the image. Thermal imaging systems use thermal radiation to create an image of the target and can see in total darkness, making them superior to image enhancement systems.

Image enhancement

Image enhancement is one of the most common types of night vision and is used in night vision goggles and other night vision devices. Image enhancement systems use a complex process to amplify the available light so that you can see an image. Most systems use a photocathode to convert the incoming light into electrons, then use a phosphor screen to convert the electrons back into visible light.

Thermal imaging

Thermal imaging is a technology that allows one to see the heat radiating off an object. Thermal imaging systems sense the temperature difference between an object and its environment to create an image of the object. These systems are superior to image enhancement systems in that they do not need any light to create an image and can see through obstructions such as smoke, fog, and foliage.

See also

• Infrared vision
• Night vision device
• Thermographic camera
• Electro-optical sensor

Night-vision Resources
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