The second video projector type to consider is the LCD (Liquid Crystal Display) projector. Unlike a CRT projector, the LCD projector is not based on the traditional projection tube. An LCD projector basically works by passing a powerful light source through a transparent LCD chip made up of individual pixels (which displays the moving video image) and projecting that image through a lens to a large screen.
The Advantage Of The LCD Projector
What makes the LCD projector very practical is that it is compact, since the LCD chip is very small. One LCD chip is hundreds of times smaller than the three projection tubes needed in CRT projectors. Other advantages of the LCD projector is its high contrast and brightness capability, as well as lower power consumption. This combination of factors make the LCD projector very portable for multimedia use, such as business presentations (even in partially lit rooms). Also, with some modification, an LCD projector can provide an excellent option for home theater use. Probably the final "hook" is that an LCD projector is fairly inexpensive, when compared to CRT types. A basic LCD projector, suitable for portable business presentations, starting well below $1,000 with units suited more for home theater use starting at about $1,000 and up, which is much less than any CRT counterpart.
Limitations Of The LCD Projector
1. A LCD projector can often times exhibit what is called "the screen door effect". Since the screen is made up of individual pixels, the pixels can be visible on a large screen, thus giving the appearance of viewing the image through a "screen door".
2. When using a business-type LCD projector in a home theater setup, the image may appear too harsh with regards to brightness and contrast.
3. Since an LCD chip is made up of a panel of individual pixels, if one pixel burns out it displays an annoying black or white dot on the projected image. Individual pixels cannot be repaired, if one or more pixels burn out, the entire chip has to be replaced.
4. Since LCD chips have a finite number of pixels, signal inputs that have higher resolutions must be scaled to fit the pixel field count of the particular LCD chip. For example, a typical HDTV input format of 1080i or 1080p needs a native display of 1920x1080 pixels for a one-to-one display of the HDTV image. However, if your LCD chip only has a pixel field of 1024x768, the original HDTV signal must be scaled to fit the 1024x768 pixel count on the LCD chip (in addition the image will also have to be letterboxed to reproduce the correct widescreen aspect ratio). This is where CRT projectors can excel over an LCD projector, since they are not limited by a fixed pixel field, they are more flexible at displaying various resolutions, due to being able to variably scan the image onto the projection tube surface.
5. As mentioned earlier, the LCD light source (bulb) in an LCD projector must be replaced periodically, depending on the projector, about every 3,000 to 4,000 hours, sometimes at a cost of several hundred dollars. On the positive side of this, a new lamp basically gives you a new LCD projector, as your original brightness and contrast are restored, and most bulbs can be self-installed by the consumer.
Variants of LCD
Other variants of LCD video projection technology in use are: LCOS (Liquid Crystal on Silicon), D-ILA (Digital Imaging Light Amplification - developed and used by JVC), and SXRD (Silicon Crystal Reflective Display - developed and used by Sony).