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Both LCD and DLP are used in projectors suitable for home theaters, but they work in quite different ways and produce slightly different results. If you ask around – particularly in electronics stores, you’re likely to be provided with a mass of information that’s confusing and often just plain wrong. So here, in an effort to clear the fog surrounding projectors, is our guide to LCD v DLP.
LCD
LCD projectors have three separate LCD panels, one for red, one for green, and one for blue components of the image being processed by the projector. As light passess through the LCD panels, individual pixels (or picture elements) can be either opened or closed to either allow light to pass through or be filtered out. In this way the light is modulated and an image projected on to the screen.
LCD projectors have historically had three main advantages over DLP. They produce more accurate colors (due to the three separate LCD panels), they produce a slightly sharper image (although this is as good as undetectable when watching movies) and they are more light-efficient, which means they produce brighter images using less power.
However, LCD projectors also have some disadvantages, although as the technology improves these are becoming less and less relevant. The first of these is pixelation, or what’s known as the screen door effect. This means that sometimes you can see the individual pixels and it looks as though you are viewing the image through a ‘screendoor.’ The second historic disadvantage of LCD v DLP is that LCD doesn’t produce absolute black, which means that contrast is less than you would get with DLP.
However, the advent of higher resoltion LCD projectors (particularly ‘HD-ready’ projectors which have a horizontal resolution of 768 pixels or greater) means that pixelation is less of a problem than it used to be. And the improved ability of LCDs to produce high-contrast images is also allowing them to be
taken more seriously by home theater enthusiasts.
DLP
Digital Light Processing (DLP) is a technology developed by Texas Instruments and it works by projecting light from the projector’s lamp onto a DLP chip, made up of thousands of tiny mirrors. Each mirror represents a single pixel and directs the light projected onto it either into the lens path to turn the pixel on or away from it to turn it off. Most DLP projectors have only one chip, so in order to reproduce color, a color wheel consisting of red, green, blue and sometimes, white filters is used. The wheel spins between the lamp and the chip and changes the color of the light hitting the chip from red, to green, blue. Each mirror on the DLP chip tilts towards or away from the lens path depending on how much of a particular colour light is required for that pixel at any given instant.
The key advantages DLP has in the LCD v DLP debate is that DLP projectors tend to be smaller and lighter, have better contrast, and don’t suffer the same pixelation problems as LCD projectors. There is one problem that some users report with DLP projectors, although it appears to only affect a very small number of people. Because of the way DLP works, at any given instant, the image on screen is either red, green, or blue. However, the images change so quickly, that the human eye doesn’t detect this and your brain puts the red, green and blue images together to make a complete frame of video. Unfortunately, some people can see the individual colours, and others can detect them enough to cause eye-strain and headaches. However, technology has improved significantly with the introduction of six-color wheels and faster rotation speeds. The rainbow effect should be a problem for even fewer people. The best way to find out if you’re affected is to try out a DLP projector, perhaps by hiring one, before you buy.
Technology in both LCD and DLP projectors is improving all the time. However, at the time of writing DLP still has a slight edge in the home theater market.
About the Author
Kenny Hemphill is the editor and publisher of The HDTV Tuner
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