The Technology War: LCD vs. DLP
July 28, 2009,
If you are new to the world of digital projectors, you won't have to shop around long before discovering that the terms LCD and DLP refer to two different kinds of projectors. They are in fact two different kinds of microdisplay imaging technology. You might not even know what LCD and DLP are before asking the obvious question "which one is better?"
The answer is simple--neither one is better than the other. They both have advantages over the other, and they both have limitations. Both technologies are much better than they used to be. The purpose of this article is to discuss how they differ today, so you can determine whether the imaging technology itself is a relevant factor in your choice of a projector.
It is important to note there is a third significant light engine technology called LCoS (liquid crystal on silicon). It is developed and marketed by several vendors, most notably Canon, JVC, and Sony. Many excellent projectors have been made with LCoS technology, including several outstanding home theater projectors that can, in the opinion of many observers, surpass the value proposition of both LCD and DLP offerings. The discussion of LCoS technology is beyond the scope of this article, and will be addressed separately in an upcoming article.
Is it 3LCD or LCD?
You may have already seen the term 3LCD on websites and in projector literature and press releases. Several makers of LCD projectors have adopted 3LCD as a marketing brand name. It is intended to distinguish the specific implementation of LCD technology found in digital projectors from the more common direct view LCD displays found in a wide variety of consumer products. In LCD projectors there are always three LCD panels, and they are always light transmissive devices rather than reflective or direct view displays. Within the projector industry, there is no technical difference between 3LCD and LCD, and the terms can be used interchangeably.
Which Technology Leads the Market?
Well, the answer to this question depends on your definition of the word "lead." As of this writing, DLP technology has a significant lead in terms of the number of models currently in production. As of this date, July 28, 2009, our database lists 704 different DLP-based models in production, as compared to 430 LCD models. Thus, DLP holds a commanding lead in the number and variety of models being produced.
However, this is not the whole story. Many of the best selling projectors these days are LCD models. As an example, at the moment, six of the Top 10 Most Popular 1080p home theater projectors on this site are LCD's, two are DLP and two are LCoS. In fact, despite the clear advantage DLP has in the number of models in production, Pacific Media Associates reports that LCD projectors held a 51% market share by unit volume in 2008. Clearly both technologies have a huge market presence, and neither one is about to emerge as the dominant player.
The Technical Differences between 3LCD and DLP
LCD (liquid crystal display) projectors contain three separate LCD glass panels, one each for the red, green, and blue components of the video signal. Each LCD panel contains thousands (or millions) of liquid crystals that can be aligned in either open, closed, or partially closed positions to allow light to pass through. Each liquid crystal behaves in essence like a shutter or blind, and each represents a single pixel ("picture element"). As red, green, and blue light passes through the respective LCD panels, the liquid crystals open and close based on how much of each color is needed for that pixel at that moment in time. This activity modulates the light and produces the image that is projected onto the screen.
DLP ("Digital Light Processing") is a proprietary technology developed by Texas Instruments. It works quite differently than LCD. Instead of having glass panels through which light is passed, the DLP chip is a reflective surface made up of thousands (or millions) of tiny mirrors. Each mirror represents a single pixel.
In a DLP projector, light from the projector's lamp is directed onto the surface of the DLP chip. The mirrors tilt back and forth, directing light either into the lens path to turn the pixel on, or away from the lens path to turn it off.
In the most expensive DLP projectors, there are three separate DLP chips, one each for the red, green, and blue channels. However, in most DLP projectors under $10,000 there is only one chip. To define color, a color wheel is used that contains (at minimum) a red, green, and blue filter. This wheel spins in the light path between the lamp and the DLP chip and alternates the color of the light hitting the chip from red to green to blue. The mirrors tilt away from or into the lens path based upon how much of each color is required for each pixel at any given moment in time. This activity modulates the light and produces the image that is projected onto the screen.
(Note: In addition to red, green, and blue filters, most color wheels contain other segments as well. A "white" or clear filter used to boost brightness is common in business/commercial projectors, and many color wheels have filters for colors other than the primaries, such as dark green, cyan, magenta, or yellow.)
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