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Learning Center

With all the new electronic technology, acronyms and high tech buzz words it's no wonder a journey into something as simple as buying a new TV or Satellite system can be confusing and at times frustrating.

What is all this talk about HDTV?

Here are definitions of some commonly used terms that you will encounter.

Ever wonder what all those video connections are on the back of your TV and components? Find out what they are and which ones deliver the highest quality video

LCD versus DLP versus Plasma TV's - Which one is better?

LCD versus DLP as related to Front Projectors


The HDTV Revolution

High-definition television (HDTV) is the biggest innovation in television technology since the introduction of color broadcasting. After decades of stagnant analog technology, the digital revolution has finally reached the television industrya transition that's just as important as the evolution from analog LPs to digital CDs. But what does it mean for you as a viewer? HDTV delivers astonishing benefits, including:

Brilliant, Saturated, Razor-sharp Images
Current analog technology broadcasts a 480 line, 4:3 viewing ratio image, while HDTV technology broadcasts a 720 or 1080 line 16:9 image. The result is up to six times more viewable pixels for unprecedented image clarity

True 16:9 Widescreen Viewing Ratio
Ordinary analog broadcasts only deliver a 4:3 viewing ratio, while HDTV delivers a full 16:9 viewing ratioa ratio which more closely matches your own field of vision and is faithful to the widescreen format of your favorite movies

SixChannel Sound
HDTV broadcasts deliver crystal-clear Dolby® digital sound with up to five channels of surround sound and a dedicated subwoofer channel, the same system used by the finest movie theaters

Fully-digital Broadcast Signal
Unlike ordinary analog technology, HDTV is pure digital for 100% accurate transmission quality without distortion, ghosting, or snow

In short, HDTV technology delivers audio and video with breathtaking fidelity. It's the ultimate home theater environment for enjoying Hollywood blockbusters, your favorite sports, and HDTV broadcast programming

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3:2 Film Correction: this is a correction that resolves picture problems created when film, which is filmed at 24 frames per second, is converted to TV format which is 30 frames per second

1080p/1080i/720p Capable: this refers to how many horizontal lines of information (or resolution) are used to create a video picture. The "i" denotes interlaced and "p" denotes progressive.

Aspect Ratio: this refers to the ratio between the width and height of a TV picture. Standard TV is 4:3 (4 units wide by 3 units high). Many new digital TV's are 16:9 wide screen aspect ratio. The 2.35:1 Cinema Scope ratio is similar to the screen format found in theaters

ATSC: Acronym for Advanced Television System Committee. Formed to establish technical standards for advanced television systems, including high definition television (HDTV)  http://www.atsc.org/

ATSC Tuner: A built in or set top tuner used for receiving OTA (over the air) local broadcast High Definition signals

Analog Broadcast: Data transmission in the form of a continuously variable wave. This format is subject to deterioration and degradation when transmitted

Cable Card: a card that fits into your TV or cable box and identifies your cable account and unlocks High Definition content for viewing

Comb Filter: Used to separate a video signal's luminance information from its color information. A digital comb filter first converts this information to a digital format for a sharper picture and not as many distracting on-screen effects. A 3-line digital comb filter is the ultimate type for the highest resolution and fewer unwanted on-screen effects

Compression: The manipulation of digital data that allows higher quality pictures to be transmitted in the small channel space currently used by traditional TV broadcasts

CRT: Cathode Ray Tube. The general term for all tubes in which one or more electron beams emitted by a cathode are periodically scanned across a phosphor screen by means of deflection circuitry. A special form of the cathode ray tube is a TV picture tube

Digital Broadcast: Data transmission in the form of the computer language of 0s and 1s. This format can be transmitted with no distortion or degradation

Digital Cable Ready (DCR) TV: A HDTV with a built in tuner that can receive digital and high definition TV signals from a cable provider without need for a expensive, bulky set-top box

DLP: A Texas Instruments innovation. Incorporates a DMD (digital micro device) which is a postage stamp sized optical semiconductor chip that contains an array of up to 1.3 million hinge mounted microscopic mirrors (each measuring less than 1/5 of a human hair). Together with a video signal, light source and a projection lens, the mirrors can reflect an ultra sharp all digital image onto a screen. Also utilizes a spinning color wheel in conjunction with the tilted mirror to produce the various pixel colors which can be one of 16.7 million colors. Advantages of DLP technology are replaceable lamps and the ability to display sustained images without "burn in"

Dolby Digital/DTS Surround Sound: Digital surround sound technologies that use 6 or more separate audio channels (right, left, center, right surround, left surround, subwoofer) to create "big screen" cinema sound. 

Enhanced Definition: 480p is an Enhanced Definition TV standard displayed using progressive scanning at a 640 wide by 480 high pixel resolution. Enhanced definition quality is above Standard Definition but under High Definition

HD-Built In TV: A TV that can display digital High Definition signals and has a built in ATSC tuner

HD-Ready TV: A TV able to display digital High Definition TV pictures, but does not have a built in ATSC tuner. Also called a HD monitor

HDTV: HDTV is an acronym for "High Definition TV." It is digital television in its best form. HDTV can transmit more than six times the amount of information as the old analog systems, making for better sound and picture quality. Current television sets are made up of 525 lines that are scanned horizontally as compared to HDTV which has 1,080 lines. Because HDTV has more than double the amount of lines as the older systems, it has more than 2 million pixels. The older analog systems contain only about 300,000 pixels (pixels are the small dots that create a clearer and more detailed picture.) Another quality of HDTV is that the screen will be much wider than the older systems. HDTV was introduced into the United States in 1998. In 1996, the FCC approved the Digital TV standard for the U.S, which offers a variety of higher quality, all digital signals for TV transmission. HDTV is not to be confused with DTV. The two are similar, but DTV is pretty much just a more generic form of HDTV. HDTV accounts for six of the 18 video formats established as part of the standards for digital television set by the Advanced Television Standards Committee or the ATSC. Of the 18 formats, these are the highest resolution formats. All six formats feature a 16:9 aspect ratio and accommodate frame rates of 24, 30 and 60 frames per second.

Interlaced Scan: On older TV's, a picture frame is scanned first with the odd line numbers and then it goes back to fill in the even numbered lines. This reduces the bandwidth required to send a picture and was popular with broadcast video. It does result in a a bit of flicker on the screen especially with moving objects.

Letter Box: Black bars that appear at the top/bottom or left/right of a TV screen when the content format differs from the screen format, for example, when watching a wide screen format DVD on a TV with traditional 4:3 aspect ratio

LCD: Stands for "Liquid Crystal Diode/Display". Sophisticated display technology that sandwiches a layer of semi-liquid, semi-solid crystals between tow sheets of polarized glass, one of which has a color filter and pixel precise voltage control system. The precise application of voltage causes the liquid crystals to respond like miniature camera shutters, blocking off light or allowing it to pass. An LCD, like DLP requires a light source behind the display. Advantages of this technology include long panel lifetime and the ability to display fixed images for extended periods of time without "burn in"

NTSC: National TV Systems Committee (USA) also the name for a TV standard (NTSC) mainly used in North, Middle and South America and Japan.

NTSC Tuner: The tuner built into traditional TV's used for receiving standard OTA (over the air) analog  signals

PAL: Phase Alternation Line. This is the 625 line color television system in use today in the United Kingdom and much of Europe

Pixels: Short for "picture elements". Single points of color, many of which together make up the video image you see on screen. The more pixels, the better the picture. Each pixel is made up of red, green and blue elements or "sub pixels"

Plasma: A plasma display contains over a million tiny glass cells that are charged with a mixture of neon and xenon. Behind these cells are colored phosphors, which are chemical compounds that emit light when energized. Each cell has three phosphors; one red, one blue, and one green. When activated by an electrode, the plasma cells emit invisible UV light. The UV light strikes the red, green and blue phosphors on the back of the display and thus creates the pixels that form the image you see on the screen

Progressive Scan: With the method a whole picture frame is painted at once. It requires the higher bandwidth afforded by HDTV, Tivo like devices and DVDs. It results is a much clearer, flicker free picture. This is most notable at the edges of the picture. Just think of it as the SVGA display as compared to the "EGA" display of the early computer monitors. Because the screen format is wide, it can display a wider picture similar to that of a movie theater's screen. Analog TV can only display "cropped" movies. In addition, HDTV broadcasts will be in the Dolby surround digital format that further enhances the TV viewing experiences.

Resolution: Refers to the number of pixels or horizontal lines that make up the on screen video image

Standard Definition: Digital broadcast format that eliminates annoying "ghosts" and "snow." Resolution ranges from the same as regular analog TV to about twice that

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TV's and other display devices can accept a wide variety of audio/video inputs from video cassette players, DVD players, Set-Top tuners, and other devices. But not all these inputs are created equal. Formats are listed below from lowest to highest quality.


RF base band signals vary widely depending on your cable and satellite provider and the type of signal they are broadcasting. RF will not support High Definition video.


Granddaddy of all video connections, this simple single coax connection can be made via BNC or RCA connector. In composite format, all video information is combined into one signal and broadcast through one RCA-type jack. It's a low-fidelity format that should be avoided if possible. Composite will not support High Definition video.


Super Video is an interface protocol first introduced by JVC with the very first S-VHS video decks about 18 to 20 years ago. S-Video sends an analog video signal on two 75-ohm coaxial cables. One conductor delivers a luminance signal, which is a black and white wide-bandwidth television signal. The other delivers a chrominance (color) signal which would normally be a composite signal riding "under" the luminance information at a frequency below the 3.58MHz 'color burst' frequency. S-Video will not support High Definition video.

clip_image010_001.jpg  RGBHV

The workhorse of commercial video production, this is analog video transmission at its finest. There are almost no limits to the practical installed length of an RGB interconnect. 100 feet is a wholly useable length! You've got to love analog for its robust nature.


The component video interface is the most common extended definition video interface in use on contemporary consumer products. In component (YPbPr or RGB)) format, the video signal is separated into three components through three RCA-type jacks. Component connections send one luminance and two phase-opposite chrominance signals on three 75-ohm coaxial cables. Component video is typically used with better DVD players, and most HDTV systems. This is still an analog signal. Regardless of other connection schemes, this is one you have to include if you want your system to be truly universal in nature.


Digital Visual Interface (DVI) is a format capable of accepting uncompressed digital data such as High Definition video, as well as signals from future digital devices. DVI is limited to about 20 feet. Beyond this length signal degradation quickly becomes evident.


HDMI (High Definition Multimedia Interface) was developed by Sony, Hitachi , Thomson (RCA), Philips, Matsushita (Panasonic), Toshiba and Silicon Image. HDMI was created as a digital interface standard for the consumer electronics market.

The HDMI protocol combines high-definition video, multi-channel audio, and inter-component control in a single digital interface. This lone interconnect has the ability to transmit uncompressed digital video and up to eight channels of audio from source to display. 

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LCD versus DLP versus Plasma TV's 

A High-Definition TV is a big-ticket item, so it's no wonder buyers are very concerned with performance issues such as rainbow effect and burn-in. But before settling on a particular TV technology, here are a few things to consider.

First, you need to decide whether you want a Microdisplay (also known as a Rear-Projection set) or a Flat Panel, such as a Plasma or LCD TV. There are three basic types of rear-projections: LCD (liquid-crystal display), DLP (digital light processing), and LCoS (liquid crystal on silicon).

                Microdisplay/Rear Projection                        Flat Panel

                                                 LCD                                                     LCD
                                                 DLP                                                   Plasma

Rear-projection TV's are thinner and lighter than the old style CRT rear-projection sets that are still around, but for the most part, you still can't hang a microdisplay on the wall. By contrast, you can easily hang a Plasma or LCD TV on the wall, but they cost significantly more, inch for inch. Each type of microdisplay has its pros and cons, but they all use a lamp that needs to be replaced every few years, so that shouldn't be a factor.

The rainbow effect mentioned earlier has been an issue specifically with DLP rear-projection sets, which use a color wheel to create red, green, and blue. Some viewers can see streaks of color on DLP TVs, especially when moving their eyes across the screen. Newer and faster color wheels, however, have significantly reduced the rainbow effect, and most people never see it at all. Furthermore, DLP has some performance advantages over competing technologies, including the deepest black levels of any projection technology (though LCD is coming on strong) and high resolution chips that show every pixel of high-definition sources.

As far as plasma TVs go, that danger of burn-in has been greatly exaggerated. Burn-in occurs when a relatively static image such as a stock ticker, a network logo, or a letterbox bar gets etched permanently onto the screen. The potential for burn-in is greatest during the first 100 or so hours of use, during which time you should keep contrast rather low (less than 50 percent) and avoid showing static images or letterbox bars on the screen for hours at a time. After this initial phase, plasma should be as durable as any television technology. Many panels also have burn-in-reduction features, such as screensavers and pixel orbiting. Under normal viewing conditions, you should have nothing to worry about.

It's important to do your homework before purchasing a big screen TV. There's a lot of junk out there that might save dollars up front, but ultimately ends up biting you in the back side with its lack of durability, lesser quality and other problems. However, before considering what brand to buy, you should first determine what kind of big screen TV you're looking for. Below is a basic description of the different technologies and some pros and cons of each technology gathered from various sources.


LCD (Liquid Crystal Display) TV

How It Works
LCD televisions are made from two transparent, polarized materials bonded together. One layer holds liquid crystals that react to electricity. This current determines whether light can, or cannot pass through a crystal. Because liquid crystals don’t emit light themselves, a secondary light source, such as a fluorescent light, is used to shine through the matrix of activated crystals to display the final image.


bulletLCD's are good for still images and make good computer monitors. So, if you're looking for a screen for TV and computer use, LCD's are a good bet.
bulletQuality LCD's have excellent brightness level pictures.
bulletLCD flat panels like Plasmas don't take up floor space and can be mounted on walls. In addition, LCD's are typically lighter than Plasma TVs.
bulletQuality LCD's have a slightly longer life than Plasmas. Roughly 60,000 hours = 27 years watching six hours per day.
bulletUnlike plasma displays, LCD televisions aren’t susceptible to burn in. As a matter of fact, LCD's excel at displaying static images.


bulletLCD's are not as good for fast-moving pictures. When an object moves quickly across the screen, the image "delays" (there are trails of pixilation or blockingess), because the screen can't keep up. The newer (2008) LCD's have very fast response times (4ms or less) so this is not an issue as in the past.
bulletLCD TVs have more difficulty in producing deep black levels than Plasmas. Given the nature of liquid crystals, they can’t block 100% of light to create a rich black. Instead, LCD's produce a dark gray.
bulletLCD image looks great when you're staring directly at it, but if you are watching from a slanted view the quality of the image can diminish greatly.
bulletLCD's are expensive over 35"
bulletLCD's sometimes have pixel failure. This isn't a common problem with top name brands, where one or two pixels might eventually die, leaving a black dot here and there. This is hardly noticeable unless you're standing directly in front of the screen (considering a 20" LCD screen has 30,000 pixels). However, in cheaper models where 10% of the pixels could go out, the TV may become unwatchable.

NOTES: There are a lot of junk LCD's out there, so stick to top brand names. Sharp is generally credited for making the best quality LCD TVs.


Plasma TV

How It Works
Based loosely on the same technology found in fluorescent lights. A 1080p plasma televisions consist of over 2 million cells. Inside each cell are two panels of glass injected with xenon gas in plasma (ionized) form. This plasma or ionized gas is then electrically charged and illuminate as red, green, and blue phosphors, also called pixels, which when combined together create the final image.


bulletTop name brand plasmas have a fairly long life, lasting about 25 years at a six hours per day.
bulletA plasma screen has a field vision of about 180 degrees without loss of picture quality. That means you can watch the screen from any angle.
bulletPlasmas are very bright (about 4-5 times brighter than the average TV).
bulletThey have great contrast ratios (enables them to show better shadow detail).
bulletThey have excellent picture response. There is virtually no delay (blockiness or pixilation) like with slower LCD and DLP TV's.
bulletDoesn't take up floor space and can be mounted on a wall.
bulletHave superior contrast ratios. Contrast ratios measure how white is white, and how black is black. A ratio of 1000:1 (which is preferable) means white is represented 1,000 times brighter than black.


bulletPlasmas have the potential for burn in problems under certain conditions. Plasmas do not make as good computer monitors as LCD's. If you were to leave the Plasma TV on for 24 hours a day and there was an image that remained constant on the screen (like a logo), you would run the risk of that image permanently burning into the screen. However, the chance of this happening is often over-exaggerated.
bulletPlasmas are not available below 37 inches.
bulletPlasmas are generally a bit more expensive than LCD's at the same size.
bulletThe phosphors that create a plasma’s stunning image are the also what make it generate more heat that other television technologies.
bulletWith over 2 million on a 1080p screen, the chance of one or two failing is strong. Each manufacturer has a limit to the number of dead pixels they will accept before considering a unit defective. Make sure to buy a name brand to ensure high initial quality. It’s also possible for pixels to fail over time. If enough pixels fail, overall picture quality will suffer.

NOTES: There are a lot of junk Plasmas out there, so stick to top brand names. Pioneer, NEC, Panasonic are generally credited for making the best quality consumer Plasma TVs. 


DLP (Digital Light Processing) TV

How It Works
DLP technology is based on a semiconductor chip called a Digital Micro-mirror Device (DMD). This chip has a matrix of microscopic sized mirrors, each one representing a pixel, which tilt to reflect, or not reflect light. Depending on the how quickly these mirrors reposition themselves, the DMD chip can recreate 1,024 shades of gray.

Color is added by placing a color wheel in front of this microscopic light show that is divided into 4 sectors: red, green, blue, and one clear sector to boost brightness. This color wheel is synchronized with the DMD to display each color so quickly that each color appears to combine and form one composite, full-color image.


bulletDLP screens are larger and are cheaper in the short-term than LCD or Plasma.
bulletGood brightness and color. DLP can illuminate a larger screen for more people at a cheaper initial cost than Plasma.
bulletAlso considered a con, DLP televisions use a light source that can be replaced. It’s much easier to replace a DLP bulb than replace an LCD’s backlight. When a plasma television burns out, it’s time to buy a new television.
bulletEven in direct sunlight, DLP televisions produce a more vivid picture than an LCD. Under the same conditions, LCD's can fall victim to the “screen door effect” where colors become less saturated, or washed out.


bulletThere's a high maintenance cost. The DLP TV is basically a video projector in a box. You have to replace the light bulb, which has limited lifetime of around 2000-3000 hours.
bulletDLP televisions are not available in a sizes smaller than 42 inches. They also can’t be mounted to the wall like a plasma or LCD.
bulletDLP's don't have as good field vision as Plasmas, meaning you can't get as good picture quality when viewing the screen at an angle.
bulletDLP's are not known for having that great of picture quality.
bulletThough not as pronounced as LCD's, DLP televisions have a small amount of lag when as they display fast moving objects.
bulletOnly present in single DMD chip DLP televisions, the “Rainbow Effect” can best be described as flashes of red, green, and blue. As mentioned above, each color is reflected one after the other so fast that you normally won’t notice a single color. However, you may catch a glimpse of one as you walk by or out of the corner of your eye.


LCOS Technology

What is LCOS technology?

Well, you could think of it as a hybrid between LCD and DLP. LCD uses liquid crystals, one for each pixel, on glass panels. Light passes through these LCD panels on the way to the lens and is modulated by the liquid crystals as it passes. Thus it is a "transmissive" technology. On the other hand, DLP uses tiny mirrors, one for each pixel, to reflect light. DLP modulates the image by tilting the mirrors either into or away from the lens path. It is therefore a "reflective" technology.

LCOS combines these two ideas. It is a reflective technology that uses liquid crystals instead of individual mirrors. In LCOS, liquid crystals are applied to a reflective mirror substrate. As the liquid crystals open and close, the light is either reflected from the mirror below, or blocked. This modulates the light and creates the image.

LCOS-based projectors typically use three LCOS chips, one each to modulate light in the red, green, and blue channels. In this it is similar to an LCD projector which uses three LCD panels. Both LCOS and LCD projectors deliver the red, green, and blue components of the light to the screen simultaneously. There is no spinning color wheel used in these projectors as there is in single-chip DLP projectors.

LCOS technology is usually very high resolution, and typically higher in price than most LCD and DLP products. There is no such thing as an SVGA resolution LCOS projector, and we know of only one very rare XGA resolution machine. Generally LCOS machines begin to appear in the SXGA (1365x1024) resolution class and higher. So by definition they are not cheap.

Nor are LCOS projectors particularly compact as compared to portable LCD and DLP units. The lightest LCOS machines to date weigh about 12 lbs. But they can get much larger and heavier than that.

So due to inherent high resolution and larger form factors, LCOS technology has not yet been adapted for cheaper mass-market portable projectors. Today's LCD and DLP projectors sell in much higher unit volumes and are more appropriate for mobile presentation, classroom, and inexpensive home theater. For this reason LCD and DLP technologies get a lot more attention. Since LCOS does not sell in the volumes that LCD and DLP do, many assume it is not as good as LCD or DLP. Nothing could be more wrong. Many well-informed videophiles seeking the most elegant home theater solutions opt for products using LCOS technology because of its unique blend of performance characteristics that neither LCD nor DLP offer.

The Advantages of LCOS

bulletLCOS projectors have several key advantages over the more popular technologies. First, due partly to inherent high resolution, and partly to high fill factors (minimal space between pixels) on the chips, visible pixelation on an LCOS machine is nonexistent. Even close up the pixel structure is less visible than you get with the high resolution 1280x720 DLP Mustang chip. So the resulting video image can be smooth as silk.
bulletSecond, with LCOS the pixel edges tend to be smoother compared to the sharp edges of the micro-mirrors in DLP. This gives them an analog-like response, whereas micro-mirrors add high frequencies that accentuate their digital nature. In practical terms, this gives the LCOS image a smoother, more natural look and feel, while DLP tends to impart a synthetic sharpness to the image that some would describe as harsh. (On the other hand, some people prefer the sharper image that DLP delivers. This is a matter of personal taste.)
bulletThird, LCOS and LCD projectors deliver continuous red, green and blue simultaneously onto the screen. Single-chip DLPs deliver color sequentially, alternating between red, green, and blue one color at a time. Though DLP projectors can be capable of delivering rich, well saturated colors, both LCOS and LCD products tend to be superior in this regard. We believe this is due to the way color is managed sequentially in the DLP machines.
bulletFourth, the absence of a color wheel means there is no chance of you or anyone you invite into your theater being bothered by rainbow artifacts, eye-strain, or headaches that some people can be susceptible to when viewing single-chip DLP projectors. This is normally not a problem for most users of DLP products. And the more expensive high-end DLP systems have higher speed color wheels that further reduce these side effects as well as the percentage of the population that are bothered by them. But the lack of a color wheel in an LCOS projector eliminates the problem entirely.

The Disadvantages of LCOS

bulletThe primary weakness of LCOS technology is contrast. Currently most LCOS products are rated in the range of 500:1 to 800:1. So they do not have the contrast performance that most DLP products are able to achieve. The use of the new high contrast screen materials helps offset this weakness to some degree. And if there is indirect ambient light in the viewing space, the differences in contrast become much less of an issue.
bulletMany LCOS projectors also have limited lamp life in the 1000 to 1500 hour range. And on certain models lamp replacements can be much more expensive than they typically are with LCD or DLP projectors. So these details should be checked before a purchase is made in order to get a clear idea of the cost of ownership.

Variations in LCOS designs

Though LCOS is a generic term, there are several different variations. The most popular LCOS implementation so far is that from JVC, which the company calls
D-ILA, for Direct Drive Image Light Amplifier.

Not all LCOS implementations are technically the same, and they should not be thought of as identical. This has practical consequences. For example, those familiar with the recent Texas Instruments study that highlighted a particular failure mode in LCD are aware that LCD panels may eventually degrade over the long run due to a breakdown of organic compounds used in their construction. JVC has made it clear that there are no organic compounds used in the D-ILA technology and therefore this failure mode does not exist with D-ILA. Thus image reliability of their products over the long run is comparable to or exceeds that of DLP. The same cannot be said for every version of LCOS on the market.

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LCD versus DLP as related to Front Projectors

Article from http://www.projectorcentral.com/lcos.htm 2003

Introduction - Keep in mind article is from 2003 so prices and technology have changed considerably

If you are new to the world of digital projectors, you won't have to shop around the market very long before discovering that "LCD" and "DLP" somehow refers to two different kinds of projectors. You might not even know what LCD and DLP are before asking the obvious question "which one is better?"

The answer is simple. Sort of. LCD and DLP each have unique advantages over the other. Neither one is perfect. So it is important to understand what each one gives you. Then you can make a good decision about which will be better for you.

By the way, there is a third very significant light engine technology called LCOS (liquid crystal on silicon). It is being developed by several vendors, most notably JVC and Hitachi. Several outstanding home theater projectors have been manufactured with this technology, and JVC's LCOS-based DLA-SX21 is currently on our list of Highly Recommended Home Theater Projectors. However the discussion of LCOS technology is beyond the scope of this article. 

The Technical Differences between LCD and DLP

LCD (liquid crystal display) projectors usually contain three separate LCD glass panels, one each for red, green, and blue components of the image signal being fed into the projector. As light passes through the LCD panels, individual pixels ("picture elements") can be opened to allow light to pass or closed to block the light, as if each little pixel were fitted with a Venetian blind. 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 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 wobble 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 very expensive DLP projectors, there are three separate DLP chips, one each for the red, green, and blue channels. However, in DLP projectors under $20,000, there is only one chip. In order to define color, there is a color wheel that consists of red, green, blue, and sometimes white (clear) filters. This wheel spins 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.

The Advantages of LCD Technology

One benefit of LCD is that it has historically delivered better color saturation than you get from a DLP projector. That's primarily because in most single-chip DLP projectors, a clear (white) panel is included in the color wheel along with red, green, and blue in order to boost brightest, or total lumen output. Though the image is brighter than it would otherwise be, this tends to reduce color saturation, making the DLP picture appear not quite as rich and vibrant. However, some of the DLP-based home theater products now have six-segment color wheels that eliminate the white component. This contributes to a richer display of color. And even some of the newer high contrast DLP units that have a white segment in the wheel are producing better color saturation than they used to. Overall however, the best LCD projectors still have a noteworthy performance advantage in this area.

LCD also delivers a somewhat sharper image than DLP at any given resolution. The difference here is more relevant for detailed financial spreadsheet presentations than it is for video. This is not to say that DLP is fuzzy--it isn't. When you look at a spreadsheet projected by a DLP projector it looks clear enough. It's just that when a DLP unit is placed side-by-side with an LCD of the same resolution, the LCD typically looks sharper in comparison.

A third benefit of LCD is that it is more light-efficient. LCD projectors usually produce significantly higher ANSI lumen outputs than do DLPs with the same wattage lamp. In the past year, DLP machines have gotten brighter and smaller--and there are now DLP projectors rated at 2500 ANSI lumens, which is a comparatively recent development. Still, LCD competes extremely well when high light output is required. All of the portable light cannons under 20 lbs putting out 3500 to 5000 ANSI lumens are LCD projectors.

The Weaknesses of LCD Technology

LCD projectors have historically had two weaknesses, both of which are more relevant to video than they are to data applications. The first is visible pixelation, or what is commonly referred to as the "screendoor effect" because it looks like you are viewing the image through a screendoor. The second weakness is not-so-impressive black levels and contrast, which are vitally important elements in a good video image. LCD technology has traditionally had a hard time being taken seriously among some home theater enthusiasts (understandably) because of these flaws in the image.

However, in many of today's projectors these flaws aren't nearly what they used to be. Three developments have served to reduce the screendoor problem on LCD projectors. First was the step up to higher resolutions, first to XGA resolution (1,024x768), and then to widescreen XGA (WXGA, typically either 1280x720 or 1365x768). This widescreen format is found, for example, on the Sanyo PLV-70 and Epson TW100, (two more products currently on our Highly Recommended list). Standard XGA resolution uses 64% more pixels to paint the image on the screen than does an SVGA (800x600) projector. The inter-pixel gaps are reduced in XGA resolution, so pixels are more dense and less visible. Then with the widescreen 16:9 machines, the pixel count improves by another quantum leap. While an XGA projector uses about 589,000 pixels to create a 16:9 image, a WXGA projector uses over one million. At this pixel density, the screendoor effect is eliminated at normal viewing distances.

Second, the inter-pixel gaps on all LCD machines, no matter what resolution, are reduced compared to what they use to be. So even today's inexpensive SVGA-resolution LCD projectors have less screendoor effect than older models did. And it is virtually invisible on the Panasonic PT-L300U, which is a medium resolution widescreen format of 960x540.

The third development in LCDs was the use of Micro-Lens Array (MLA) to boost the efficiency of light transmission through XGA-resolution LCD panels. Some XGA-class LCD projectors have this feature, but most do not. For those that do, MLA has the happy side effect of reducing pixel visibility a little bit as compared to an XGA LCD projector without MLA. On some projectors with this feature, the pixel grid can also be softened by placing the focus just a slight hair off perfect, a practice recommended for the display of quality video. This makes the pixels slightly indistinct without any noticeable compromise in video image sharpness.

Now when it comes to contrast, LCD still lags behind DLP by a considerable margin. But recent major improvements in LCD's ability to render higher contrast has kept LCD machines in the running among home theater enthusiasts. All of the LCD projectors just mentioned have contrast ratios of at least 800:1. They produce much more snap, better black levels, and better shadow detail than the LCD projectors of years past were able to deliver.

The Advantages of DLP Technology

There are several unique benefits that are derived from DLP technology. One of the most obvious is small package size, a feature most relevant in the mobile presentation market. Since the DLP light engine consists of a single chip rather than three LCD panels, DLP projectors tend to be more compact. All of the current 3-pound miniprojectors on the market are DLPs. Most LCD projectors are five pounds and up.

Another DLP advantage is that it can produce higher contrast video with deeper black levels than you normally get on an LCD projector. DLP has ardent followers in the home theater world primarily due to this key advantage.

While both technologies have seen improvements in contrast in the past two years, DLP projectors still have a commanding lead over LCDs in this regard. Leading-edge LCD projectors like the Sony VPL-VW12HT is rated at 1000:1 contrast, and Sanyo's PLV-70 is rated at 900:1. Meanwhile, the latest DLP products geared toward home theater like NEC's HT1000 are rated as high as 3000:1. Less than two years ago the highest contrast ratings we had from DLP were in the range of 1200:1.

This boost in contrast is derived from Texas Instrument's newer DLP chip designs, which increase the tilt of the mirrors from 10 degrees to 12 degreees, and features a black substrate under the mirrors. These changes produced a significant advance in contrast performance that simply did not exist before.

A third competitive advantage of DLP over LCD is reduced pixelation. These days it is most relevant in the low priced, low resolution SVGA class of products. In SVGA resolution, DLP projectors have a muted pixel structure when viewed from a typical viewing distance. Conversely, most SVGA-resolution LCD projectors tend to have a more visible pixel grid. This is entirely irrelevant if you are using the projector for PowerPoint slide presentations. However, it is more problematic for a smooth video presentation. For this reason, we don't normally recommend SVGA-resolution LCD projectors for home theater. Conversely, the revolutionary InFocus X1 is a DLP-based SVGA resolution projector. It is selling now for under $1,000 and is an incredible deal for the home theater enthusiast on a limited budget.

In XGA and higher resolution, DLP technology pretty much eliminates pixel visibility from a normal viewing distance. However, the latest WXGA resolution LCDs do so as well. So with higher resolutions, differences in pixelation are not the big competitive battleground they used to be. DLP continues to hold a small competitive edge, but the dramatic advantage of DLP over LCD no longer exists. The screendoor effect is receding into history as a problem of days gone by.

A Potential Problem with DLP: The Rainbow Effect

If there is one single issue that people point to as a weakness in DLP, it is that the use of a spinning color wheel to modulate the image has the potential to produce a unique visible artifact on the screen that folks refer to as the "rainbow effect," which is simply colors separating out in distinct red, green, and blue. Basically, at any given instant in time, the image on the screen is either red, or green, or blue, and the technology relies upon your eyes not being able to detect the rapid changes from one to the other. Unfortunately some people can. Not only can some folks see the colors break out, but the rapid sequencing of color is thought to be the culprit in reported cases of eye strain and headaches. Since LCD projectors always deliver a constant red, green, and blue image simultaneously, viewers of LCD projectors do not report these problems.

How big of a deal is this? Well, it is different for different people. For some who can see the rainbow effect, it is so distracting that it renders the picture literally unwatchable. Others report being able to see the rainbow artifacts on occasion, but find that they are not particularly annoying and do not inhibit the enjoyment of the viewing experience. Fortunately, the majority of the population either cannot detect the rainbow artifacts, or if they can they are not overly bothered by them. The fact is if everyone could see rainbows on DLP projectors the technology never would have survived to begin with, much less been embraced by so many as a great technology for home theater video systems. Nevertheless, it can be a serious problem for some viewers.

Texas Instruments and the vendors who build projectors using DLP technology have made strides in addressing this problem. The first generation DLP projectors incorporated a color wheel that rotated sixty times per second, which can be designated as 60Hz, or 3600 RPM. So with one red, green, and blue panel in the wheel, updates on each color happened 60 times per second. This baseline 60Hz rotation speed in the first generation products is also known as a "1x" rotation speed.

Upon release of the first generation machines, it became apparent that quite a few people were seeing rainbow artifacts. So in the second generation DLP products the color wheel rotation speed was doubled to 2x, or 120Hz, or 7200 RPM. The doubling of the refresh rate reduced the margin of error, and so reduced or eliminated the visibility of rainbows for many people.

Today, many DLP projectors being built for the home theater market incorporate a six-segment color wheel which has two sequences of red, green, and blue. This wheel still spins at 120Hz or 7200 RPM, but because the red, green, and blue is refreshed twice in every rotation rather than once, the industry refers to this as a 4x rotation speed. This further doubling of the refresh rate has again reduced the number of people who can detect them. Nevertheless it remains a problem for a number of viewers even today.

How big of a problem is the rainbow issue for you?

If you've seen earlier generation DLP machines and detected no rainbow artifacts, you won't see them on the newer machines either. The majority of people can't see them at all on any of the current machines. However there is no way for you to know if you or another regular viewer in your household are among those that may be bothered either by visibly distracting rainbows, or possibly eyestrain and headaches, without sitting down and viewing a DLP projector for a while.

Therefore, if you think you've identified a DLP projector that is just right for your needs but you are not sure whether this will be a problem, there is an easy solution. Find an alternative product that is either LCD- or LCOS-based that would be your second choice if you find that DLP won't work for you. Then find a customer-service oriented dealer who sells both models, and who will allow you to switch the DLP product for the alternative after testing it out for a few days. There are a number of service-oriented Internet dealers who will be happy to make such arrangements, and there are plenty who will not. But if you choose a dealer who is more interested in your satisfaction than in closing a quick deal (and they are definitely out there), you will end up with a thoroughly satisfying solution in the end.

A Potential Problem with LCD: Long Term Image Degradation

Texas Instruments recently released the results of a lab test conducted last year which highlighted a failure mode in LCD technology that does not exist with DLP. Given enough time, it appears that LCD panels, primarily those in the blue channel, will degrade, causing shifts in color balance and a reduction of overall contrast. The test did not include a large enough array of test units to draw any conclusions about anticipated rates of degradation under normal operating conditions.

However it is possible that those who invest in an LCD projector may find that eventually the LCD panel and polarizer in the blue channel may need replacement. This is not much of a problem if the unit is under warranty. But if it isn't, the replacement of an LCD panel will represent an unpleasant incremental investment in your projector that you were not anticipating. (See more details on TI's test and our thoughts on it.)

The Current State of the Art

The largest developers and manufacturers of LCD technology are Sony and Epson. These companies have no interest in standing by and letting Texas Instrument sweep the digital projector market with its competing DLP technology. So competition has driven both the LCD makers and Texas Instruments to improve their respective products in the ongoing battle for market share.

While LCD technology has made significant improvements in contrast performance over earlier generation machines, DLP maintains its lead in contrast. Meanwhile LCD projector makers have continued to emphasize key advantages in color fidelity, color saturation, and image sharpness for data display.

Both LCD and DLP are evolving rapidly to the benefit of the consumer. The race for miniaturization has produced smaller yet more powerful projectors than we might have even imagined possible just a couple of years ago. Light output per pound has increased dramatically. And video quality on the best LCD and DLP projectors now surpasses that available in a commercial movie theater.

ProjectorCentral continues to recommend both LCD and DLP projectors for a variety of applications. For mobile presentation it is hard to beat the current group of 3-pound DLPs on the market. However LCD products like the Epson 735c at 4.3 lbs make it clear that LCD is still a very strong contender in the mobile presentation market. And for larger conference rooms that require higher light output and greater connectivity, LCD technology holds a commanding lead.

When it comes to home theater, DLP has continued to make competitive advances in color, contrast, and image stability that have served to make it a technology preferred by many for home theater systems. But the fact is that both DLP and LCD continue to improve, and both are capable of delivering much higher quality video for home theater than they ever were before.

Which technology is the best? Well, it depends. Both technologies have advantages, and both have weaknesses. Neither one is perfect for everything. So the technology war continues. The only clear winner in sight is you, the consumer.

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Last modified: May 02, 2012