I know of three approaches to night vision devices Intensification or amplification of the existing visible light coming from an object. Comparison of infrared or thermal radiation from an object with the environment or background. Illumination of the object or field of view with radiation outside the spectrum visible by humans 1. Image intensification is called a "passive" system, so-called because it emits no visible energy that would give away the observer's position. The technique involves wide-aperture lenses that collect and guide even very dim light to an electronic sensor that amplifies and displays whatever is in the field of view. This "low-light" technology was made practical in the late 1960s, during the Vietnam War. 2. Infra-red sensing equipment employs a principle long ago recognized in certain non-human species that were able to see light in the near-infrared spectrum, just beyond human vision. This passive technique depends on the object having some intrinsic heat, either biologic or mechanical/chemical, or its having been heated by an external source of heat, such as sunlight. 3. Illumination in the near-infrared spectrum was found to be practical in the 1930s and 1940s and applied to military needs in WW2. Infrared spotlights were made that, without excessive power demands, could emit infrared light without visible traces. The emissions reflected from an object were then detected by equipment tailored to match the emissions.
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night vision, infrared, military,
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