The Technology War: LCD vs. DLP
July 28, 2009,
Many of the advantages and limitations of 3LCD have already been touched on above within the context of the DLP discussion. However, there are several advantages of LCD not yet discussed, and some of the issues already noted warrant a recap and/or further expansion. The following are the key benefits of LCD technology:
Better price/performance in HT products. The primary key to the success of LCD products in the home theater market is their tremendous price advantage. In the 1080p niche in particular, LCD products deliver outstanding image quality performance for the money. Moreover, they are generally loaded with extra features that don't appear on DLP models in the same price range, if they are offered on any DLP model at all.
The price advantage of LCD over DLP is most obvious in consumer/home theater products. There is no similar disparity in pricing on commercial products built for mobile presentation and conference room use. One reason is that DLP makers can use the cheaper 2x speed wheels on most business products, whereas it is mandatory to have high speed color wheels and the faster electronics associated with them on products designed for home theater.
Higher contrast in HT products. Many LCD projectors built for home theater have achieved better overall contrast performance and deeper black levels than DLP models. This is specifically the case on LCD models using inorganic LCD panels and auto iris technology. Inorganic panels are more expensive to produce, so they are not used in cheaper, commercial grade business projectors. They achieve higher contrast due in part to the fact that the resting position of the liquid crystal is closed (i.e., black), and voltage is required to open it. This is the opposite of traditional organic LCDs wherein the resting position is open (maximum light transmission), and voltage is required to close it. The inherent contrast advantage of inorganic panels has made LCD substantially more competitive in the home theater marketplace. ANSI contrast in particular has seen significant improvement. In our measurements, LCD projectors with organic panels typically run in the range of 250:1 ANSI contrast, whereas the models with inorganic panels have been reaching performance levels of 400:1 to 450:1.
3LCD vendors have been aggressive in developing effective auto iris systems which contribute an incremental perceived contrast advantage on screen. There is no technical restriction that we know of that would prohibit DLP vendors from doing the same thing. But it would add further cost to DLP projectors that are already at an apparent cost disadvantage relative to LCD in the home theater market. There is also a perception among vendors that DLP contrast, while not leading edge, is sufficient, so enhancement via auto iris is not vital. Thus, most DLP vendors have been slow to incorporate auto iris systems on DLP projectors being marketed for home theater.
Fewer artifacts/greater image stability. As noted previously, dithering artifacts and rainbow artifacts are unique to single-chip DLP projectors. Since these artifacts do not exist on LCD products, it is not unusual to perceive a more stable video image on an LCD projector when viewed side by side with a DLP counterpart in a similar price and performance class. The LCD's video image can look cleaner and more free of noise.
Sharper image with data display. Since LCD pixel structure is more sharply defined that DLP pixel structure, it tends to render a sharper image. This is most noticeable in lower resolution business products (SVGA and XGA), and specifically with data display. It is in these resolutions that LCD's screendoor effect is somewhat more visible in a video image, but the advantage is that the sharper pixel definition can produce a sharper display of data. By comparison, a DLP projector in SVGA and XGA resolution can look a bit soft when displaying data images.
On higher resolution products the difference in apparent sharpness is minimal, and it is a non-issue with video display on 1080p products. Both technologies can produce very sharp images in 1080p, and any perceived differences in sharpness typically have to do with factors unrelated to the display technology, such as lens quality and video processing.
Greater installation flexibility in HT products. LCD projectors built for home theater often feature 2.0x zoom lenses and extensive vertical and horizontal lens shift. This makes them easy to install just about anywhere. By comparison, DLP projectors usually have short zooms with little or no lens shift. Fixed throw angles limit the projection geometry, and often dictate where a DLP projector must be placed in order to accommodate a given screen size and location.
For the DIY home theater enthusiast on a budget, the lens flexibility of LCD models has great appeal. For the fact is, most DLP projectors need to be ceiling mounted, and most LCD projectors don't. Thus they save the extra cost of a ceiling mount and long run video cables. They also eliminate the prospect of having to run cables through walls and ceiling, or living with an unsightly track of cables across the ceiling.
Better light efficiency, less power usage. LCD technology is inherently more light efficient. For the most part LCD projectors use lower wattage lamps to produce the same image brightness that you'd get from DLP. This is most noticeable when comparing LCD projectors to DLP projectors that have no white segment in the color wheel. As an example, compare two currently popular 1080p home theater projectors--the Panasonic AE3000 LCD projector uses a 165-watt lamp to produce 1600 ANSI lumens. Meanwhile, the Sharp Z15000 DLP projector needs a 250-watt lamp to get the same 1600 lumens. That can make a noticeable difference in power consumption. It can also make a difference in the amount of heat being generated by the projector's exhaust in the viewing room.
Unknown lifespan of LCD panels. Given enough prolonged exposure to high intensity UV light and extreme heat, the organic compounds used in most LCD panels are expected to degrade over long periods of time. This degradation can lead to a discoloration of the image and a reduction in contrast. The only way to fix it is to replace the damaged LCD panel, which is typically a cost-prohibitive proposition. You are normally better off buying a new projector.
The big question of course is how long the panels will last. There is no good data on this subject that has been compiled by an independent lab and published for general consumption. LCD vendors do not typically acknowledge LCD degradation can occur, so they don't make any representations about expected life. In general, most LCD vendors maintain that to the degree LCD panels might be subject to eventual degradation, it will be beyond the practical life of the product.
One trusted and very experienced industry source who develops products using both LCD and DLP technology believes that LCD panels have a lifespan in the range of 4,000 to 10,000 hours, with the lifespan depending on how bright the projector is--the brightest LCD light cannons will produce the most stress on the panels resulting in quicker degradation. Low brightness models such as those made for home theater will produce the least stress, and are expected to last longer.
Texas Instruments has performed several tests on LCD lifespan over the past seven years. Based on these tests, they believe that LCD panels will degrade faster than the LCD vendors are willing to admit, and certainly more quickly than the 4000 hours just quoted. The 3LCD camp's response is that TI's tests have been performed by running LCD projectors continuously 24 hours a day, 7 days a week, for several months straight. According to 3LCD and Epson, since the projectors used in TI's lab tests were never designed for a continuous operation high-stress duty cycle, the results are not indicative of what the typical user would experience.
The introduction of inorganic LCD panels is an important new development that is germane to this issue. Inorganic LCD panels, in theory, should not be subject to the same degradation patterns as organic LCDs, simply because the organic compounds that fail under intense heat and UV light are not present in inorganic LCDs. However, the LCD camp will not confirm or deny any anticipated differences in panel life because as a matter of policy they do not discuss the issue at all. Texas Instruments has not commented on the expected lifespan of inorganic LCDs either.
Lower contrast ratings in business products. Most commercial and education LCD projectors are made with the relatively inexpensive organic LCDs and no auto-iris. Contrast ratings on these models typically run in the 400:1 to 700:1 range. Meanwhile, DLP projectors in the same resolution, lumen, and price class can often be rated at 2000:1 or higher.
In reality, this constitutes more of a marketing disadvantage than a technical one. In most business/commercial and classroom settings, projection display is done with room lights on. With moderate ambient light--enough for children in a classroom to take notes for example--a projector's contrast rating is largely irrelevant. Actual contrast on screen with moderate ambient light is typically in the range of 50:1 regardless of the theoretical contrast potential of the projector. But for buyers who are not aware of the huge impact of ambient light on contrast ratios, the apparent advantage of DLP over LCD in contrast ratings can appear to be more significant than it really is.
Susceptible to dust spots. Since LCD light engines are not sealed, it is possible for dust particles to alight on the LCD panels, thereby creating a dull, indistinct spot on the projected image. This usually causes little distraction when displaying static images such as data or photographs. But in full motion video, seeing a stationary element in a moving picture can be extremely distracting.
When dust lands on an LCD in the red or blue channel it is rarely visible enough to create a distraction. But when it occurs in the green channel it can become quite visible. Some vendors have provided methods by which the user can remove the dust without having to send the unit in for cleaning. Sanyo's home theater models come with a hand pump that will blow a jet of air across the panels, but since we've never seen a dust spot on a Sanyo projector, we've never been able to test the device. Other than this sort of solution, packing the projector up and sending it to a maintenance depot for cleaning is the method of last resort for getting the projector back into serviceable shape.
LCD makers claim that today's air filter systems are superior than those of the past, and that dust contamination is highly unusual if the filters are cleaned and replaced as per normal maintenance instructions. Most LCD vendors cover dust removal under warranty, which is a good reason to buy LCD projectors with extended warranties.
When we review projectors, we have no way to assess the actual risk to the user of dust contamination on any particular model. We can say that it is rare for us to notice dust spots on LCD projectors that we get in for review, or on units that we keep in operation for ongoing reference purposes. However, it is easy for users to forget to clean filters since under normal usage vendors recommend this be done every two months or so. When filters are left unattended, the user increases the risk that dust will eventually find its way into the projector.
The fight for market share between 3LCD and DLP continues at a fevered pitch. It is a fascinating thing to watch as vendors of both technologies continue to innovate to stay a step ahead of the competition. Picture quality in digital projectors has improved dramatically over the past decade with significant increases in contrast, resolution, and color performance. Prices have dropped like a rock, and high quality projection systems that once were within financial reach of wealthy consumers or businesses who really needed them, are now within the budgets of mass consumers. Thus the consumer is the ultimate beneficiary of the intense competitive struggle between the DLP and 3LCD technologies.
As we've tried to make clear in this article, both DLP and 3LCD have key advantages over the other. They also both have limitations that the buyer should be aware of. But in the end, we see better image quality performance today from both LCD and DLP than we've ever seen in the past. And it just keeps getting better.
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