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Infrared (IR) filters can block or pass light in the IR section of the spectrum, depending on the design, and are available for a number of purposes. Some are used in imaging, while others provide safety for devices that emit infrared light, acting as heat suppressors to prevent overheating when the device is in operation. A number of optics companies produce IR filters for a range of devices. These tools are available from camera shops, electronics stores, and other facilities that carry optics equipment.
Some IR filters are IR cutoff filters. They block emissions of infrared light, with a level of sensitivity determined by the design. The packaging usually indicates the specific wavelength it blocks, to allow the customer to determine whether it will suit a given need. A common use for such filters is in devices with light bulbs that tend to heat up, like projectors. The filter can block the heat in the infrared area of the spectrum to keep the device operating at a cooler temperature.
Others are IR pass filters. Pass filters are most commonly seen in photography. These filters can block all visible light and only allow IR radiation to pass, allowing photographers to take images in the IR range of the spectrum. Such photography can create visually striking images and can also be useful for security purposes, where people may want to see sources of IR in a scene. IR filters can be built into the structure of a device like a camera, or added over the lens to provide additional filtration.
IR filters are also available to block infrared emissions for cameras that are sensitive to them. Sometimes IR creates noise in an image, especially with digital cameras, which have very delicate sensors. If photographers notice repeat problems with images, they may experiment with different filter types to determine if blocking light in some ranges of the spectrum can make their images sharper and cleaner.
Devices like binoculars and telescopes can also be fitted with IR filters. The filter manufacturers classify their products on the basis of the range of light blocked, and technicians can select the most appropriate product to filter out visual noise or to take infrared images, depending on their needs. Some of these filters need to be custom made, in the case of specialty equipment that may have nonstandard eyepieces or openings. The filter can also be designed to block other ranges of the spectrum, if necessary.