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Selecting a Video Projector
Technologies
CRT - Uses three CRT's to produce image and provide light for projection. Convergence and focus of image at screen plane.
Pro: Wide range of computer video formats accommodated at high quality, accurate video/data color reproduction.
Con: Large, heavy, expensive. Cannot be moved without setup. Limited light output requires darkened room. High maintenance requirements, CRT's have limited operational life.
LCD- Uses 3 transmissive LCD panels to modulate external light source. Convergence established during manufacturing; only user optical adjustment is focus (and zoom if applicable).
Pro: Smaller, lighter, less expensive than CRT design. Can easily be moved from site to site with no setup required. Brighter models do not require complete room darkening. Models with zoom lenses permit flexible location in room. Low maintenance requirements.
Con: The use of fixed resolution LCD panels requires pixel mapping/scaling to accommodate all computer graphics standards which are not at the native resolution of the projector. This may result in the loss of some detail information in the display. Pixelation of the image may be objectionable for some uses. Light distribution of projected image may be uneven (bright center, dark edges). Color temperature of lamp may adversely affect color of images, especially video.
LCD-Light Valve (ILAã [Image Light Amplifier])- Uses three small CRT's to drive reflective LCD panels which in turn modulate an external light source.
Pro: Can provide very bright images at high resolution. Good color temperature results in accurate color rendering of computer and video images.
Con: Large, heavy, expensive. Cannot be easily moved. High maintenance requirements.
DLPã (Digital Light Processing)- Uses one, two or three DMDã (Digital Micromirror Device) chips containing a matrix of pixel-sized movable mirrors which reflect light from an external source through a common lens to the screen. Projectors employing fewer than three DMD chips use compromised color components or a rotating color filter wheel to produce color images.
Pro: High efficiency-produces bright image with smaller lamp than LCD design (or brighter images with the same size lamp). Good image contrast and color reproduction in 3 chip models.
Con: One- and two-chip designs produce color and temporal artifacts--especially in moving video. Fixed pixel design requires scaling/pixel-mapping to deal with all but native resolution sources (see LCD projector description for caveats in this area). Moderately expensive in three-chip designs. This is a new technology so the operational life of the DMD's and maintenance requirements are unknown.
D-ILAã (Direct Drive Image Light Amplifier)- Similar in design to LCD but external light source is reflected off front of LCD panel rather than transmitted through panel.
Pro: Same as LCD but more efficient; smaller lamp for the same brightness (or same lamp for greater brightness). Higher native resolution than other fixed pixel designs.
Con: More expensive than LCD. Pixel mapping/scaling still required for sources not at native resolution. Only one manufacturer (Hughes-JVC) using this design. New technology- no track record or maintenance history.
Criteria for selecting type of projector
Type and level of sources to be projected: Computer (VGA, SVGA, XGA, SXGA), video (VHS-quality or greater). Higher resolution sources may require more expensive projector or different technology. Use of scaling in fixed pixel designs (LCD, DLPã , D-ILAã ) will require demonstration of projector with intended sources.
Portable or fixed installation: Some designs cannot be easily moved due to weight and setup requirements. Lack of ambient light control in rooms may require brighter projector. Zoom lens provides flexibility in projection location. Size/weight of projector may be an important attribute for frequent moves.
Acquisition cost/cost of operation: The initial projector cost and the cost of operation (CRT/lamp life/cost, required maintenance levels and intervals) needs to be examined to determine the cost to support the projector over its lifetime
Service life of the projector/future growth: Will the projector be replaced in five years (typical) due to obsolescence or is this a longer term investment? A higher resolution/more expensive unit may be a better choice in the latter case.
Criteria for selecting a particular model of projector
Once the above criteria are taken into account, certain technologies are usually ruled out by price, setup requirements, projection light capabilities, etc. At that point, spec sheets from the major players in the remaining technologies can be examined.
For CRT designs these would include Sony, NEC, Barco.
For LCD: Sharp, Proxima, Mitsubishi, Barco, 3M.
For LCD-Light Valve (ILAã): Hughes-JVC, AmPro.
For DLPã: various.
For D-ILAã: JVC.
The native resolution and the maximum resolution supported should match the user requirements.
Brightness levels as reported in the spec sheets are usually wildly optimistic-if possible compare ANSI lumens to ANSI lumens, not to foot candles, candelas, Nits, etc.
Image size at the intended projection distance and the ratio of the zoom lens should match the intended projection venues. In the end, an on site demonstration of the final choices is mandatory before purchase.
Criteria for selecting a vendor
Using a vendor who represents a particular manufacturer and has the models in stock, as opposed to a vendor who can obtain the projector from another vendor is important. A vendor who actually represents the manufacturer has access to the latest information and upgrades for the units he sells as well as a vested interest in making sure that the client is satisfied. He also has the ability and the motivation to go back to the manufacturer with any problems which may surface. Vendors who have dealt with UCLA for a period of time are usually the best choice. They know our basic needs and are used to dealing with the University's purchasing system. In any case, an on site demonstration using the client's computer and software is required before any purchase decision can be made.
Links to video and data projector manufacturer websites
Rick Holmes
8/7/98
