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Three video projector technologies in use today include CRT, LCD, and DLP. A CRT (Cathode Ray Tube) projector is based on proven television technology; there are three small cathode ray tubes (one each for primary colors red, green, and blue) coupled with a light magnifying lens. A CRT projector's image is not limited to a fixed pixel field so it can effectively display a variety of resolutions. It can produce very dark blacks and a full range of colors, and the projection tubes have a long life expectancy (potentially 20,000 hours). However, its large size makes it inconvenient for travel, it must be used in a very dark room, and all three projection tubes must be replaced if one fails. Furthermore, CRT projectors are fairly expensive.
An LCD (Liquid Crystal Display) projector passes a powerful light source through a transparent LCD chip consisting of individual pixels, and it projects the image on a large screen through a lens. It works well for business presentations because it is compact and portable, has high contrast, and consumes little power. However, LCD projectors can exhibit what it known as the "screen door" effect. This is when the individual pixels are visible on-screen, appearing as if the viewer is looking through a screen door. When used in a home setting, the image presented by an LCD projector may appear too bright and harsh. Additionally, if one or more pixels burns out, the entire chip must be replaced. The light source in an LCD projector costs several hundred dollars, and it must be replaced about every 1,500 hours.
A DLP (Digital Light Processing) projector employs a chip known as a DMD (Digital Micromirror Device) that displays the video image. The tiny mirrors tilt rapidly as the image changes; color is added as light passes through a high speed color wheel and is reflected off the micromirrors. This technology is also used in some movie theaters for feature film presentation. The advantages of a DLP projector include color accuracy, no "screen door" effect, and lower power consumption. Like an LCD, the light source in a DLP projector must be changed every 1,000 to 2,000 hours, but DLP projectors are quickly becoming a favorite of users everywhere.
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