If you have gone through our introductory guide to front projection television, you know that the fun with front projection starts with a home theater projector and an appropriate projection screen.

To-day's high resolution LCD and DLP video projectors are capable of projecting huge pictures while still maintaining very good image quality.

However not all projector technologies deliver equally when used in the home theater.

In this article, we discuss the pros and cons of the most common projector technologies in use today - namely CRT, LCD, and DLP - with respect to their use in a front projection setup in the home theater.

In reality, CRT projectors are being phased out while a fourth technology is slowly entering the market, liquid crystal on silicon (LCoS). LCoS technology first debuted on top-dollar theater projectors, though now, the first sub-$5,000 models have started to emerge. Still, there are only a few LCoS models on the consumer market.

Please note that this is not a How-it-Works article, but a short discussion that takes a look at the pros and cons of the different home theater projector technologies in use. For a how-it-works description of the different projection technologies, please check out our How-It-Works: Video Projection article.

Which is the most appropriate video projection technology for Home Theater Use: CRT, LCD or DLP? 

The CRT Projector (Cathode Ray Tube)

Up to a few years ago, home theater projectors were all based on the Cathode Ray Tube (CRT) - this is the same glass display tube found on television sets. Three small bright CRTs (one for each primary color: red, green, and blue), coupled with an optical lens setup, project a color image onto a large screen in a darkened room.

With the proper video processing circuitry, CRT size, and lens combination, a CRT projector can produce excellent high resolution images.

The image in a CRT projector is scanned with an electron beam (just as in a regular glass tube television). This means that the CRT projector is not limited to a fixed pixel field, as is the case with DLP and LCD video projectors. This makes the CRT projector the best option when flexibility to display variable resolutions is the main concern.

In addition, a CRT projector can produce the blackest blacks of all projector types as well as the full range of color, giving the CRT projector the ability to project the most film-like images of all home theater projector technologies.

The CRT projector is also characterized by its long projection life - as long as 20,000 hours before proceeding with tube replacement. With LCD and DLP video projectors, the light source must be replaced every few thousand hours (anything between 1,000hrs and 4,000hrs is typical for most home theater projectors), to maintain optimum brightness and contrast. This leads to an added regular expense of several hundred dollars with every lamp replacement.

Nothing is perfect: The CRT Projector has a number of drawbacks worth taking note of:

• In comparison to LCD and DLP type home theater projectors, a CRT projector is relatively large and heavy. A CRT type projector designed to project images onto a large screen, with enough brightness, may be the size of a 20-inch TV. This makes the CRT projector less portable.

• CRT projectors are not as bright as LCD or DLP projectors; therefore, viewing in total darkness is essential for best results.

• A CRT projector has to be converged properly for best image reproduction. The three projection tubes (red, green, and blue) found in a CRT projector need precise alignment so that colors are mixed correctly - improper alignment leads to color halos. This can be a complex and timely process that has to be done by a professional. 

• Worst still is that if one of the projection tubes fails, all three have to be replaced - at a huge cost - in order to provide the correct color and brightness balance.

• A full size CRT video projector capable of delivering giant 150" to 200" projections is very expensive. Expect to pay anything between $10,000 to $20,000 for a high quality  CRT projector employing 9-inch projection tubes. This also explains why CRT-based home theater projectors are becoming even less common in use - their LCD and DLP counterparts are capable of delivering huge bright image projections at typically 50% cost of a CRT video projector.

The LCD Projector (Liquid Crystal Display)

The first fully digital home theater projectors to appear on the market were Liquid Crystal Display projectors.

The LCD projector works by passing a powerful light source through a transparent LCD chip made up of individual pixels (which display the moving video image); the image is then projected through a lens onto a large screen. In very simple optical terms, one may consider the LCD projector as a slide projector with the slide being replaced by the transparent LCD panel.

What makes the LCD projector very practical as a home theater projector is its compact size, since the LCD chip is very small - just a very small fraction of the size taken by the three projection tube setup used in CRT projectors.

Other advantages of the LCD projector include high contrast and high brightness image levels, as well as lower power consumption. These make the LCD projector - a most suitable portable video projector for multimedia use, e.g. for business presentations in partially lit rooms.

But probably the most important issue is that the LCD projector is fairly inexpensive. This renders the LCD projector as an affordable option for both general use, and in the home theater.  LCD projectors suitable for portable business presentations are available at under $1,000 while a good quality entry-level High Definition LCD home theater projector would not cost more than $2,000; the Panasonic PT-AE700U Home Cinema LCD Projector is a case in point. This is surely much less than any CRT counterpart.

This does not mean that the LCD projector is the prefect solution; it still has a number of disadvantages worth thinking about:

• A LCD projector may exhibit what is known as the 'screen door effect'. Unlike its CRT counterpart, the screen in an LCD projector is made up of individual pixels - which can be visible during large size image projections. This may render the projected image as if it is being viewed through a "screen door".

• The cheaper business-type LCD projector may not be suitable as a home theater projector. Unless an LCD projector is designed specifically for home theater use, the image may appear too harsh with regards to brightness and contrast levels.

• Any burnt-out pixel in the LCD chip may display as an annoying black, white, or colored spot on the projected image. Individual pixels cannot be repaired; if there are a number of burnt-out pixels, the entire chip has to be replaced at substantial cost.

• Since an LCD chip has a finite number of pixels, signal inputs that have higher resolutions, must be scaled-down to fit the pixel count of the LCD chip.

A typical 1080i HDTV input signal requires a native display resolution of 1920 x 1080 pixels for a one-to-one display of the HDTV image. This may be well above the available number of pixels - hence in the case of an XGA projector say, the original HDTV signal must be scaled to fit the 1024x768 pixel count on the LCD chip. In addition, the image will have to be 'letterboxed' to reproduce the correct widescreen aspect ratio; this means that in effect, the scaled down image will have a resolution of 1024 x 576 pixels to maintain the same 16:9 format of the HDTV signal.

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This is where CRT projectors excel over LCD; CRT projectors are not limited by a fixed pixel count; due to their ability to variably scan the image onto the projection tube surface, they are capable of correctly displaying different video formats,

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• There is also the lamp replacement issue. The light source in an LCD projector has to be replaced periodically - typically every 1,000 to 4,000 hours - depending on the projector, at a cost of several hundred dollars per replacement.

On the positive side, a new lamp basically gives you a new LCD projector, as the lamp replacement restores the original brightness and contrast levels. Lamp replacement is most often, a simple job than can be done by the owner without the need for any professional assistance.

The DLP (Digital Light Processing) Video Projector

DLP based home theater projectors represent the fastest growing type of video projectors - in terms of sales - in use today. Digital Light Processing devices - more commonly know as DLP, forms part of a new family of video projectors based on digital micro-mirror device (DMD) technology.

Like LCD, the actual image is displayed on a chip - however, the chip used in a DLP projector is different; it employs anything between one and two million mirrors arranged in an array, with each mirror representing a pixel; these mirrors modulate the reflected light according to the incoming video signal.

For full operational details of the DMD chip, please refer to our 'Projection Television: How-It-Works' article. For the scope of this guide, it is enough to point out that each micro-mirror tilts very rapidly - with the degree of tilt being in response to the image signal to produce the image grayscale information.

Color is added as light passes through a high-speed rotating color wheel and is reflected off by the micromirrors on the DLP chip as they rapidly tilt towards or away from the light source. The degree of tilt associated with each micromirror, coupled with the rapidly spinning color wheel, determines the color structure of the projected image. The light reflected by the micromirrors is then sent through a lens setup that projects the image onto the screen. 

The advantages of this system render DLP projection technology suitable for both business presentations as well for use in home theater projectors. This in view that DLP projectors produce a much 'smoother' looking image than its LCD counterpart  - a feature that renders DLP projectors more suited to home theater use.

The DLP chip is also more robust and less prone to individual pixel (or mirror) failures; this contrast heavily with LCD panels where the individual pixel burn-out rate is much higher. 

Other advantages of the DLP video projector include:

• Excellent color accuracy

• No 'screen door' effect (as in the case of LCD projectors) due to its micro-mirror construction,

• Compact and light

• Low power consumption

• High contrast and brightness

Still, the DLP projector has a number of drawbacks as well:

• As with LCD, each DLP chip has a finite number of pixels - hence a fix image resolution.

• Though DLP projectors don't exhibit the 'screen door' effect associated with many LCD units, yet they can exhibit what is referred to as the 'rainbow effect'. This is synonymous with all color wheel projector technology and is the brief flash of colors (like a small rainbow) when the viewer looks rapidly from side to side on the screen or from screen to anything else in the room.

Fortunately, this does not occur frequently and many people do not have sensitivity to this effect at all. Some of the latest DLP projectors use a higher rotating speed for the color wheel to eliminate the rainbow effect almost completely  

• And just as with LCD projectors, the light source in a DLP projector must be changed every few thousand hours.

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Concluding Remarks: Which is better - LCD or DLP?

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Historically, DLP projectors boasted better contrast and black levels, and delivered a more film-like image rendering them a favorite choice with home theater enthusiasts when it comes to home theater projector choice.

At the same time, LCD projectors had better color saturation, improved brightness levels, with less fan noise and lower operating temperatures. Until a couple of years ago, LCD projectors were also cheaper.

But because of improvements in both technologies, these designations matter less and less to the end-user, as performance and price for both DLP and LCD home theater projectors are more or less equal. DLP have equaled the color saturation originally only possible on LCD video projectors, while LCD technology have improved to such an extent that it has practically closed the gap with DLP in the area of black level performance

However, there still remain a few minor differences between LCD and DLP projectors that are inherent to the respective technology: home theater DLP projectors tend to be a bit smaller, because the technology takes up less space. In addition, DLP projectors still have a slight edge over LCD when it comes to black levels. On the other hand, LCD projectors still have a brightness advantage.

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Additional Information: If you think that the home theater projector option represents a possible solution to your needs, we suggest that you also take a look at our Projection TV Buying Guide for additional information on what to look for when planning a projector purchase. To view our selection of product reviews, please check out the following links:

• Front Projection: Video Projector Reviews

• Rear Projection TV Reviews