Projection Technology

While flat panel TVs may look great, the price premium is substantial. For the majority of people, projection technology offers the best value. Projection TVs come in two formats, front and rear projection. Front projections are like slide projectors. They offer the largest possible screen size, but are difficult to place, require a dark room and a dedicated screen (not a blank wall) for best results. Since front projectors are considered a secondary display since they do not work well in daylight, we'll focus on rear projection TVs only.

CRT RPTV; $1500 to $2500; 47 to 65-inch

CRT rear projection is the original big screen TV technology. They're big, heavy, and consume a lot of power. You can't see a thing in the daytime. The viewing angle is narrow that you won't get a good picture sitting off to the side. Over time (years), the alignment of the electron guns goes off resulting in an unfocused picture. All that said, CRT rear projection is the cheapest big screen technology out there and for the group of viewers sitting in the middle of the room with the lights turned off, it offers the best picture quality of any TV at any price. That’s right, a $2500 65” rear-projection TV will look better than a $15,000 plasma. Burn-in is something to be concerned about, but when you factor in inflation, you can still replace a CRT RPTV almost twice and still come out ahead. The real disadvantage to the CRT RPTV will always be size. Are you likely to move to a new home soon? Will it fit in your home without rearranging the furniture?

Three-chip LCD: $2500 to $7000; 42 to 70 inches

LCD rear projection takes an approach similar to the classic overhead projector. In this approach, the light from a high-intensity bulb is split into polarized red, blue, and green beams. The LCD panels can control the amount of light reaching the screen by changing the angle of polarization of the liquid crystal inside each cell. If you recall from high school physics, if the polarization is parallel, all the light goes through and when it is perpendicular, no light goes through. There is precise control over the amount of light filtered. Gray can be produced by only partially polarizing the light. When the red, green, and blue light combine, you get your full color picture.

Unlike computer LCD monitors or flat panel LCD monitors in which the individual red, green, and blue pixels are located side by side, LCD rear projection TVs are projected over each other. Combined with the use of a high-intensity discharge bulb rather than a cold-cathode fluorescent, rear projection LCD TVs offer better overall color than PC monitors.

3-chip LCD technology offers excellent color and more brightness than a CRT rear projection TV. TVs are relatively thin (~1 foot) and light, and offer wide viewing angles appropriate for a big party. Unfortunately, because LCD panels cannot completely filter out light, the color black ends up being a very dark gray. Lastly, part of the LCD panel circuitry blocks the light going through, resulting in a faint grid pattern and a picture that appears slightly soft.

Single-chip DLP

With DLP, a high-intensity light bulb illuminates a group of almost a million microscopic mirrors. Each microscopic mirror can be tilted to bounce the light toward the screen or away from it. This can happen several thousand times a second. So if you can imagine that a mirror is rapidly cycling between on (reflect the white light toward the screen) and off (angle the light away from the screen), a gray picture is produced. To get a color picture, the light passes through a rotating colored filter. Because the mirrors of the DLP device move so quickly, alternating monochrome images end up producing a normal color picture. That is, a red square immediately followed by a blue square in a thousandth of a second will appear purple to our eyes.

DLP offers better contrast and brightness than LCD. Since the circuitry for controlling the microscopic mirrors are not in the path of the light, images also appear sharper than LCD TVs. Unfortunately, the rotating color wheel cannot provide the same color purity as a three-chip design. In particular, black and white scenes or fast moving action can produce the appearance of rainbows at the edge. Imagine if the purple square was moving so fast that the red and blue did not perfectly overlap, you'd end up seeing a purple rectangle with a blue and red border. The majority of individuals are not sensitive enough to notice the color errors produced by the spinning wheel and this isn't a problem. However, others will complain of a headache after watching a movie on a single-chip DLP screen. To minimize the rainbow effect, some high-end DLP TVs spin the wheel at faster rates than their budget competitors. In the next 5 years, we may begin to see affordable three-chip DLP rear projection TVs which will alleviate this problem but until then, this remains an Achilles heel of the technology.

1 Mpixel single-chip LCoS: $3500 to $4000; 55 to 62 inches

1 Mpixel 3-chip: $3500 to $4500; 52 to 61 inches

2 Mpixel 3-chip LCoS: $8000 to $20000; 60 to 82 inches;

LCoS, or "Liquid crystal on silicon" offers a glimpse at the future. In this variant of LCD technology, light is reflected off the colored LCD rather than filtered through it. This can offer even superior brightness and contrast to DLP. Like single-chip DLP, single chip LCoS (marketed by Philips) uses a spinning color wheel. This means that the "rainbow" artifacts can also be a problem.

However, the majority of LCoS designs (Sony SXRD, JVC D-ILA, Mitsubishi Alpha, and the stillborn Sears Veos) are three chip designs and therefore offer the same color offered by three-chip LCD. Moreover, whereas conventional DLP and LCD technology are limited to approximately one megapixel of resolution, the Sony SXRD, Mitsubishi Alpha, and Sears Veos LCoS products offer 2 megapixels of resolution.

With the contrast and brightness of DLP, the color of three-chip LCD, and unparalleled resolution, HDTVs using 1920x1080 LCoS technology truly offer the best of all worlds. The main disadvantage is price. Very few people can afford the technology and DLP and LCD rear projection TVs offer a better overall value.