Night vision apparatus lights the darkness.
Darkness has always represented the unknown, the forbidden, the frightening. So what better way to illustrate the advances possible through technology than by conquering the darkness? Night vision apparatus does just that. Several techniques extend vision into the darkness. Each uses a different part of the electromagnetic spectrum.
The Electromagnetic Spectrum
High energy gamma and X-rays, ultraviolet light, visible light, infrared light and radio are all versions of electromagnetic waves. Optical and infrared wavelengths are often measured in nanometers (nm), which are billionths of a meter, or in micrometers (µm), which are millionths of a meter. Visible light is roughly the region of the electromagnetic spectrum from about 400 nm to about 700 nm; near-infrared radiation covers the range from 700 nm to about 2 µm. The mid-infrared wavelengths are from about 2 µm to about 5µm, and wavelengths longer than 5 µm are called the far-infrared.
Intensified
The most common, least expensive style of "night vision" uses an image intensifier of some sort. These imagers generate electrons from the small amount of visible light in a dark scene. Some intensifiers take electrons generated by a photocathode and amplify them by accelerating them through a multichannel plate, other versions generate electrons within a charge-coupled device (CCD) and amplify them within the same device, reducing noise. These detectors work with visible and near infrared light, with wavelengths from about 400 nm to about 900 nm.
Active Illuminator
CCD cameras are sensitive not only to visible light, but also to near-infrared radiation, typically responding to wavelengths as long as 950 nm. Active illuminators take advantage of the CCD sensitivity beyond visible wavelengths. They incorporate "flashlights" at near-infrared wavelengths to shine on the scene, and detect the reflection of those waves from objects in the scene. These active illuminators shine and detect light at wavelengths between 750 nm and 900 nm.
Thermal Imagers
Every object radiates energy. The amount and wavelength of the energy depends primarily upon the object's temperature. The sun is about 5,000 degrees Kelvin (8,500 degrees F.) and shines a bright yellow visible light. Much colder objects, like human bodies, have a temperature of about 300 K, which means their peak wavelength is around 9 µm, well out in the low-energy far-infrared. Thermal detectors are sensitive to low energy mid-infrared and far-infrared wavelengths, but they are significantly more complex and expensive than intensified imagers or active illuminators.
Tags: from about, about about, from about about, visible light, amplify them, electromagnetic spectrum, generate electrons