The Great Technology War: LCD vs. DLP
July 11, 2005,
Performance Advantages: LCD vs. DLP
Both of these technologies have been evolving rapidly over the last five years. Both of them are much better than they used to be, and the radical differences we used to see between them have narrowed quite a bit. There are still noteworthy differences, but the story is a classic example of how open market competition drives improvements in technology.
Historically speaking, one traditional benefit of LCD was that it delivered better color saturation than was possible from a DLP projector. That was because in most single-chip DLP projectors built for the commercial presentation market, a clear (white) panel is included in the color wheel along with red, green, and blue in order to boost light 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. This is not an issue with data display as colors are plenty vibrant with a data signal. But it is something to consider if you plan to use the projector for high quality video display.
To compensate for the lack of color saturation and to improve color accuracy, many of the DLP-based products made for home theater now have six-segment color wheels that feature two sets of red, green, and blue filters. Meanwhile the white segment is eliminated. (Some wheels actually have seven or eight segments to include a dark green in addition to the red, green and blue.) These wheels boost color accuracy and color saturation while sacrificing light output. This is a good trade-off for video applications because high quality front projection video depends on high image contrast and color saturation, not lumen output. Front projection systems are always best viewed in a dark environment where high lumen output is not required, and can actually be detrimental. Thus the home theater-oriented DLP projectors have closed the gap with LCD in the area of color saturation, whereas the DLP products built for high-brightness commercial presentation still tend to have a weakness in this area.
Another area where these two technologies have differed is in image sharpness with data applications. LCD can usually deliver a slightly sharper image than DLP at any given resolution. The difference between the two is noticeable in the display of detailed computer data, like financial spreadsheets. However, there is no visible difference in sharpness with video. This is not to say that DLP will project a fuzzy spreadsheet--it doesn't. When you look at a spreadsheet projected by a DLP projector it looks sharp 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 a bit sharper in comparison.
A third traditional advantage 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. Thus LCD products dominate the bright end of the performance range. However, brighter DLP models are beginning to encroach upon LCD here as well. Last September, there were about 60 projector models in the database rated between 3000 and 6000 ANSI lumens at retail prices under $10,000. All of them were LCD projectors with the exception of one DLP model. At this writing, there are 90 models rated between 3000 and 6000 lumens under $10,000. Seventy-five of them are LCD and fifteen are DLP. Still, the brightest of the DLPs in this group is only 4000 lumens. So LCD continues to maintain a significant competitive edge in light output per dollar spent.
LCD projectors have historically had three weaknesses, all of which are more relevant to video than they are to data applications. The first is visible pixelation--the ability to see the discrete pixels on the screen. The second is commonly referred to as the "screendoor effect" because it looks like you are viewing the image through a screendoor. The screendoor effect is caused by the space between the pixels, known as the inter-pixel gap. The third weakness is not-so-impressive black levels and contrast, which are vitally important elements in a good video image. LCD technology has in the past had a hard time being taken seriously among some home theater enthusiasts (understandably) because of these flaws in the image.
However, LCD has made strides in these areas. The inter-pixel gaps on LCD panels have been reduced and physical resolution--the number of pixels on the screen--has been increased. In the early days of the digital projector industry, resolutions were low, generally at VGA (640x480) or lower. The industry then stepped up to SVGA (800x600), and then to XGA resolution (1,024x768) and higher. Many of today's widescreen format projectors use either 1280x720 or 1366x768 resolution displays). With each step up in the number of pixels that produce the image, visible pixelation and the screendoor effect have been reduced. At the new pixel densities, visible pixelation is usually eliminated at normal viewing distances.
Second, the inter-pixel gaps on all LCD machines, no matter what resolution, have been reduced compared to what they use to be. So even today's inexpensive SVGA low-resolution LCD projectors have less screendoor effect than did earlier models.
Since DLP technology creates a pixel by reflecting light from a tiny mirror, its edge definition is softer and less well-defined than LCD (this is what accounts for the slightly softer image in detailed spreadsheet presentation, but also DLP's traditionally smoother image in video). So for the most part, at any given resolution, DLP still holds an advantage over LCD in visible pixelation. However due to the recent advances in LCD technology you need to stand closer to the screen to see the differences than you used to.
Now when it comes to contrast, LCD still lags behind DLP by a considerable margin. But both have made significant strides forward. Just three years ago typical LCD projectors were rated at 400:1 contrast or lower while comparable DLP models were at 600:1 or 800:1. But major improvements in both technologies have boosted contrast ratings to new levels. Many commercial DLP projectors are rated at 2000:1 these days, and models built specifically for home theater carry ratings of up to 5000:1.
Meanwhile, nine months ago there were 38 LCD projectors rated at 1000:1 contrast or higher in our database. Today there are 63. And the addition of dynamic aperture control is able to boost contrast on LCD projectors to unheard of heights. Sony's VPL-HS51 has a contrast rating of 6000:1, and the Panasonic AE700 is rated at 2000:1. With contrast performance in this ballpark, LCD products continues to remain competitive with DLP, although most DLP models will still outperform comparably priced LCD products in contrast.
The consumer should bear in mind that while high contrast is critically important for high quality video presentation in a darkened environment, it is entirely irrelevant in commercial data presentation in a fully or partially lit room. Once you have lights on in the room, black levels get hammered, and the real contrast on the screen usually drops to well below 20:1 no matter what the theoretical contrast rating on the projector is. For "lights on" data presentations, adequate lumen output is essential, and contrast is meaningless. Accordingly, many commercial LCD projectors continue to to be sold despite contrast ratings of 400:1 or lower. The reason is that they produce a substantial amount of light and razor sharp data images for extremely competitive prices. They are designed for commercial presentation environments in which the contrast rating is a non-issue.
Finally, one of the key advantages of DLP over LCD is small package size, a feature most relevant in the mobile presenter market. Since the DLP light engine consists of a single chip rather than three LCD panels, DLP projectors tend to be more compact. There are 52 DLP projectors currently on the market weighing 4.0 pounds or less. Meanwhile, there are only seven LCD models in this weight category, six of which are from Epson. However, all six Epson models are near the top of the list when all of the sub-4 lb models are ranked by lumen output. So LCD's advantage in light efficiency manifests itself across the entire spectrum of projection products.
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