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A Guide to Rear Projection HDTV Technology
Pros and Cons of CRT, DLP, LCD, and LCoS Rear Projection Technologies

Are you thinking of going BIG? Rear projection gives you the biggest screen for your money, this despite the drastic fall in price of big screen plasmas and LCD HDTVs.

What’s more, the new low prices of flat panel TVs is forcing rear projection TV makers to further cut down on the price of their latest RPTVs. This is making big screen rear projection TVs even more affordable than ever.

Samsung HLT6187S 61" Slim LED Engine 1080p DLP HDTV For our detailed review, click here.

Analysts are predicting that rear projection TVs will at some point disappear from your favorite store as more RPTV makers are forced to exit the market.

Whether this will ultimately take place depends on the upcoming developments in rear projection technology. In particular, Texas Instruments - the DLP chip maker -  is predicting that new RPTVs will soon be just seven inches deep.  

This move towards slimmer designs is expected to slow down the present drop in sales of RPTVs. In addition, the cheaper price tag and the lower power consumption of rear projection HDTVs give RPTVs an added bonus over other display technologies.

But... is this enough for the survival of the RPTV set?

In our opinion, it is still a bit too early to predict. In any case, if as analysts are saying, the demise of rear projection TV is inevitable, it will surely take a couple of years for this to happen. In the meantime, you can enjoy the latest in rear projection technology from major brands and get that big screen TV at a truly affordable price.

The main problem many consumers face when choosing a rear projection TV, is simply one of getting confused by the different rear projection technologies; the latter seem to be flourishing despite that many are predicting the downfall of RPTVs.

The reality is that TV makers are constantly coming up with new developments in rear projection. This is leading to improved picture quality, longer lamp life, reduced set-up effort, and equally important, more stylish and slimmer cabinet designs.

In particular, present-day designs make RPTVs look more like the latest flat-panel TVs than the traditional ‘big’ box television. This is more than understandable; the biggest competition rear projection TVs face comes from plasmas and LCD HDTVs.

We believe that as things stand today, rear projection HDTVs can still appeal to those looking for the cheapest big screen option while enjoying the best in picture quality that the latest rear projection technology can deliver.

Rear Projection Technologies:

Rear projection systems can be grouped under two main categories – those based on the old CRT tube, and microdisplay chips - namely rear projection systems based on DLP, LCD, and LCoS technologies.

CRT-based Rear Projection Systems

Up to a few years ago, the majority of RPTVs were tube-based systems using the traditional CRT to generate the picture image for projection onto a large screen. Relatively heavy and bulky by today standards, these box-type TVs are literally disappearing fast. In fact, the only CRT projection TV presently available from a major TV maker we are aware of is the JVC AV 56P777 - 56" I'Art Pro 1080i CRT rear projection HDTV, which is a remanent from the JVC 2006 line-up.

On the upside, CRT-based rear projection HDTVs are relatively inexpensive in comparison to other technologies. The 56-inch JVC AV56P777 RPTV referred to here is presently selling at amazon for approximately $1,500. In comparison, both the LCoS 55-inch Sony KDS-55A3000 and the DLP 56-inch Samsung HL-T5687S are selling at around $1,800.

CRT-based systems Pros/Cons Summary list:

Microdisplay Rear Projection Systems

Microdisplay-based rear projection HDTV sets represent the latest in rear projection technology. These systems use one or more (three - one for each primary color) microchips that contain hundreds of thousands of pixels to build up the image. Competing microdisplay rear projection technologies include DLP, LCD, and LCoS.

Contrary to CRT systems which depend on the light produced by the tube itself, microdisplay systems use an external light source – normally in the form of an HID lamp. This either bounces light off the microchip surface in the case of DLP and LCoS, or pass the light beam itself though the chip in the case of LCD, to produce the image. This also explains why microdisplay-based rear projection HDTVs come with a substantially brighter picture than their CRT equivalents.

At the same time, the use of a lamp means that this has to be replaced regularly – typically every 3000 to 8000hrs, depending on technology, and equally important on the conditions of use. For example, too bright an image leads to a reduced lamp life. In most cases, lamp replacement can be done by the user, but this in itself brings about a typical expense of $250 or more for each replacement lamp.

Latest developments in this area use alternative light sources to the traditional lamp that have a much longer lifetime. For example, the use of an LED light engine in the latest Samsung HL-T87 series means that light source replacement takes place at 20,000hrs.

Another distinct characteristic of microdisplay-based rear projection HDTVs is that these HDTV sets are substantially lighter and more compact than CRTs RPTVs.

Present-day designs of the latest microchip RPTVs - when viewed from the front - resemble more that of flat-panel plasma and LCD HDTVs rather than the big box look of traditional CRT RPTVs. Some of the latest slim type models are so compact that they can literally be wall-mounted. In general however, microchip RPTVs require a table stand to bring the rear projection HDTV screen at eye level. 

DLP (Digital Light Processor) Rear Projection HDTVs:

Based on the Digital Micro-mirror Device, or DMD - originally developed by Texas Instruments, DLP rear projection is the most popular of all three microchip-based rear projection technologies, with a wide range of products covering both 720p and 1080p HDTV sets. In particular, 720p rear projection HDTVs are among the cheapest big screen TVs one can find on the market. At the same time, present trend with all major TV makers is to move away from this HD format in favor of 1080p HDTV. In fact, present rear projection HDTV line-ups from major brands comprise more 1080p sets than 720 HDTVs.

Unlike LCD rear projection HDTVs, DLP-based 1080p HDTV sets use wobulation to produce a 1080p image from a 960 x 1080 pixel microchip. The whole process makes use of an optical actuator to offset (wobulate) the image by ½ pixel 120 times a second in the case of 1080p 60Hz HDTV, to create the 1920 x 1080, 1080p 60Hz image.

This ½-pixel displacement also helps soften the pixel edges - leading to a seamless more film-like image with no visible pixel structure. In contrast, LCD based systems tend to break up in what is often referred to as ‘screen-door effect’ when viewing takes places at too close a distance. However, this image break up on LCD RPTVs is less noticeable with 1080p LCD based systems due to their higher pixel fill.

Some tend to complain that wobulation leads to a too soft an image in comparison to other image technologies – however this is all a matter of personal taste.

Interesting here is that Samsung – the world’s largest DLP TV maker – has literally decided to ride over this wobulation technique in order to come up with 1080p HDTV sets that are 3-D compatible. In fact, Samsung HL-T87S (reviewed here), can display 3D content from your PC. You will need a pair of LCD shutter glasses plus appropriate Samsung software to run on your PC and an IR emitter to synchronize the shutter action on the LCD glasses. According to Samsung, the whole 3-D kit would retail for $100. The resultant 3D image carries a resolution of 960 pixels horizontally in that the second frame used in the 3D image build-up is technically a different (displaced) image and therefore, it does not represent additional image detail to the previous frame.

Traditional lamp-based DLP rear projection HDTVs have one major shortcoming. These sets use a spinning color wheel to create the red, green and blue primary color information necessary to build up the displayed image. The use of the color wheel makes these sets susceptible to what is known as the ‘rainbow effect’. Some people can literally catch a glimpse of the color separation on the screen manifesting itself as a brief splash of color. This is the so called ‘rainbow effect’; it arises mainly when there is a small moving bright object over a predominantly dark background.

The use of new color wheel design rotating at substantially higher speeds (several 1000 revs per minute), has significantly reduced the occurrence of rainbows. In fact, as things stand today, the majority of people who watch a DLP never see rainbows at all, and the few who do usually see them only occasionally. If this were not the case, then DLP would not lead the rear projection TV world.

At the same time, if you happen to be one of those people that are sensitive to this rainbow effect, then we say... avoid traditional DLPs; instead either move on to other technology, or use LED-based sets. The latter do away with the color wheel in favor of a separate colored LED light source – one for each primary color – that flashes in sequence to produce the color information.

And if you are not sure about your susceptibility to rainbows… test before you buy.

Another issue with DLP rear projection HDTVs is that these sets tend to introduce a bit more low-level video noise than LCD or LCoS based systems. However, this noise issue is often well controlled by the noise reduction features found on many DLP HDTV sets.

DLP-based systems Pros/Cons Summary list:

LCD Rear Projection TVs

LCD rear projection TV technology represents the second most popular rear projection technology – after DLP, with major manufactures include Hitachi, Panasonic, LG, and Sony. However… The recent announcement on part of Sony – the major player in the field - that it will exit the rear projection TV business by February 2008, may severely impact the survival of this display technology. True that there remain major players in the field but the real driving force behind LCD rear projection so far was Sony.

Panasonic PT-61LCZ70 61" 1080p LIFI LCD Rear Projection HDTV

In comparison to DLP, LCD rear projection technology main advantage is that these sets are not prone to rainbows. LCD RPTVs use three LCD panels – one for each color – instead of the conventional color wheel separator used in DLPs.  This should prove to be a big advantage to those sensitive to rainbows, otherwise this is a non-issue.

Some non-LCD manufactures tend to argue that due to the organic nature of LCDs, the image quality of LCD RPTVs will degrade over time. While in essence this is true, yet today’s LCD displays are such that the useful lifetime of the organic matter used in the LCD chip by far exceeds the product life span in actual use.

From a price perspective, LCD rear projection HDTVs tend to sell at a price that is in line with that of DLPs – generally, these sets are not cheaper but close enough to provide tough competition to the DLPs.

On the downside, LCD RPTVs do not support the same black level performance as that of DLPs and LCoS. This is an inherent technical limitation due to the way LCD work to block light from the light source.

As with all lamp-based RPTVs, LCD rear projection HDTVs also require regular lamp replacement that may eventfully lead to a high cost of ownership. However, as with LED light technology developed by Samsung in DLP sets, Panasonic has managed to come with an innovative light technology for its LCD rear projection TVs that according to Panasonic last as long as the TV set itself! Branded as LIFI™ (LIFI stands for LIght FIdelity), this innovative Panasonic light source has various advantageous over the traditional 'High Intensity Discharge' (HID) lamp. These range from an exceptionally long life, stable performance, relatively accurate primary colors, and equally important, a quick start-up time (typically turn on time is 10 seconds against the 30 to 60 seconds necessary with traditional lamps).

And like their LCoS counterparts, LCD-based rear projection HDTVs also have more white-field uniformity issues than DLP; this non-uniformity becomes more apparent when displaying extensive flat content over the whole screen area. The extent of this uniformity issue varies from model to model.

Another disadvantage of LCDs is mainly one of image quality, more specifically image pixel breakup as a result of what is referred to as screen-door effect. This mainly happens with 720p HDTVs when viewing takes place at too close a distance to the screen. At too close a viewing distance, the viewer may be able to notice the space between adjacent pixels – leading to what may appear as a faint grid of pixels. With the latest high resolution 1080p HDTVs, this pixel break-up is practically a non-issue thanks to the higher pixel-fill. However, if you sit at too close a distance, it is still possible to see the pixel structure.

LCD-based systems Pros/Cons Summary list:

LCoS Rear Projection HDTVs

LCoS (Liquid Crystal on Silicon) represents an interesting technology. It is a hybrid between DLP and LCD. Like DLP, it is a reflective display technology that uses liquid crystals instead of the individual mirrors on a DMD chip to modulate the light falling onto the reflective silicon substrate. And like LCD, it is also a transmissive technology in that light has to pass through the liquid crystals prior to reaching the substrate. This explains why LCoS has something from either of the other two display technologies.

Thus, like their DLP counterparts, LCoS rear projection HDTVs are characterized by excellent black levels and saturated colors. Images do not exhibit any pixel breakup thanks to a greater pixel fill than that possible with LCDs.

Equally important with those sensitive to rainbows, rainbows are not an issue with LCoS in that like LCD, LCoS-based rear projection technology makes use of a three-chip set-up, one for each of the three primary colors.

On the downside, like LCD, LCoS do suffer from some brightness uniformity as already expressed earlier on. LCoS is also the most expensive of all rear projection technologies.

LCoS is also the technology that has been through some hard times especially with early generation technology. Major TV makers like Philips, Mitsubishi, and Toshiba – once great supporters of this technology – left the LCoS rear projection business at the early stages of its development in favor of other TV technologies.

Today, the only players left are Sony with its SXRD range, and JVC with the HD-ILA brand. And Sony will soon be out as well…

Sony (SXRD): Sony has already declared that it will drop its rear projection HDTV business by February 2008 in favor of its flat-panel LCD TV line. This represents a severe hit not only to LCoS, but to rear projection technology in general. This in view that Sony’s line of LCoS based rear projection TVs, rebranded as SXRD (Silicon X-tal Reflective Display) some two years ago, represents among the very best one can find in HDTV.

Sony Bravia SXRD KDS-60A3000 60" 1080p Rear Projection HDTV

Thanks to their exceptional picture quality, the Sony SXRD range has always proved to be extremely popular despite their relatively higher price tag. Their KDS-A3000 series recently reviewed on our site is a proof of the exceptional picture quality supported by the latest developments in rear projection LCoS based HDTVs.

JVC (HD-ILA): JVC has been producing LCoS RPTVs since early 2004 under the HD-ILA (High Definition Direct-drive Image Light Amplifier) brand. Since then, JVC continued to come up with top performers – as is the case with their latest ultra-slim JVC HD-58S998 58" 1080p HDILA Projection HDTV.

LCoS-based systems Pros/Cons Summary list:

A final advice:

• For additional information on rear projection HDTVs, please visit our Rear Projection TV Reviews section.

• If you need help setting up your rear projection HDTV, we advise to use one of the latest set-up DVDs. We highly recommend the Avia II set-up DVD, an exceptional AV calibration tool suitable for both the novice and the expert. Another interesting TV calibration tool is the Digital Video Essentials HD, but this is more suitable for advanced users. Both set-up DVDs include information on the latest HD technologies.

  For more information on set-up discs, visit our Guide to HT Set-Up DVDs.

• Prior to any decision, we advise to do some research of your own. Rear projection HDTVs remains the cheapest in terms of screen estate, but they still represent substantial investment. See what other customers had to say about the rear projection HDTV of interest. There is no better insight to a product than to go through what others had to say about their experience following their purchase.

  A good starting point is the customer feedback posted on the amazon site. Just click on the  link below to access the full range of RPTVs available at amazon.com, then follow through the 'Customers Reviews' once you access the respective product page:

Rear Projection TVs

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