A monitor filter is a device that is attached in some way to a computer screen to protect the screen, hide its display from people who are not directly in front of it, or reduce the amount of glare, static or radiation that is being emitted. The filters can be made from a few different substances, but they most often are a plastic, such as acrylic, or are made from composite materials. The transparent viewing surface can be coated in a special film to prevent glare and create interference, or it can be constructed from a material that has the innate properties desired. The monitor filter can come with special mounting brackets so it hangs in front of the monitor or special strips so it can be attached to the front, or it can be a thin sheet of plastic that fits into the recess of the monitor, especially in the case of liquid crystal displays (LCDs).
One of the main reasons why a monitor filter is used results from the design of traditional cathode ray tube (CRT) monitors, which generally have curved glass surfaces on the viewing area of the screen. This glass and the curve easily reflect light from the surrounding environment, causing glare that can obscure the screen. A monitor filter interrupts this light, removing the glare from the screen. Another concern with CRT monitors is the amount of radiation emitted by the monitor, which monitor filters are able to mitigate.
LCD monitors, also called flat-screen monitors, do not emit as much radiation as a CRT and also are generally flat without a glass coating on the surface, automatically reducing the amount of glare on the screen. While a monitor filter might still be needed to act as an anti-glare filter, a more common purpose often is privacy. A filter can be made in a way that allows it to create interference, meaning the monitor will appear black or blurry when viewed from angles not perpendicular to the screen.
Two other uses for a monitor filter are to protect the screen from physical damage and to reduce the amount of static that is emitted. CRT monitors generate static electricity that can be transferred to a person and then potentially damage computer hardware. Some filters include a grounding clip that can be attached to a piece of metal, absorbing and dissipating the static charge as it is generated. The plastic filters also can be an easy way to keep a monitor clean, preventing nicks, scrapes and damage from oils on the fingers if touched.