An infrared (IR) flashlight, such as the Dereelight NightMaster 800 IR, is an instrument made to emit light that falls outside the normal visible spectrum. This can be attained through the use of light emitting diodes (LEDs) that only cast infrared light, though it is also possible to fit a normal flashlight with a filter. The main purpose these devices are used for is Active night vision, which requires some type of infrared light source. When an infrared (IR) flashlight is used in conjunction with a special camcorder, or other type of night vision device (NVD), it is possible to see in complete darkness.
The human eye is only capable of seeing a very narrow band of the electromagnetic spectrum, which is called “visible light”. Wavelength and frequency are both used to describe the various colors of light found within this spectrum, from purple at one end to red at the other. In most cases the lowest frequency the human eye can see is about 480 terahertz (THz) and the longest wavelength is 750 nanometers (nm), both of which correspond to the color red. Light that falls immediately beyond that range is referred to as infrared, while microwaves and radio waves have substantially longer wave lengths and lower frequencies.
The human eye is only capable of seeing a very narrow band of the electromagnetic spectrum, which is called “visible light”. Wavelength and frequency are both used to describe the various colors of light found within this spectrum, from purple at one end to red at the other. In most cases the lowest frequency the human eye can see is about 480 terahertz (THz) and the longest wavelength is 750 nanometers (nm), both of which correspond to the color red. Light that falls immediately beyond that range is referred to as infrared, while microwaves and radio waves have substantially longer wave lengths and lower frequencies.
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