Introduction
When searching for a new projector, you will soon see the terms "LCD" and "DLP" as
they refer to two types of technologies. CRT based systems seem to be on there way
out fast as they are large, noisy, hard to calibrate, and break down frequently.
The black levels are still better using CRT technology and are the remaining benefit.
With the advent of the gray screens and better digital technologies, this difference
in black level has shrunk.
You might not even know what LCD and DLP are before asking the obvious question
"which one is better?" LCD and DLP each have unique advantages over the other,
and 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. There
is a third light engine technology called LCOS (liquid crystal on silicon) that
is being developed by several vendors, most notably JVC.
The Technical Differences between LCD (non LCOS) 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 red, green,
and blue. However, in DLP projectors typically 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 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 turn on and off 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 controls red, green, and blue independently through three
separate LCD panels. That means you can adjust brightness and contrast of each color
channel individually. In LCD projectors with good on-board controls, this can enable
the projector to achieve very good, and sometimes excellent color fidelity. In most
single-chip DLP projectors, color is fixed and defined to a large degree by the physical
color wheel and the color temperature of the lamp which changes over its usable life.
So while DLP technology has improved dramatically at reproducing accurate color, good LCD
projectors still have a slight performance edge in this area.
LCD also delivers a somewhat sharper image than DLP at any given resolution. The difference
here is more relevant in data than in video. This is not to say that DLP is fuzzy - it isn't.
When you look at a financial spreadsheet projected by a DLP projector it looks clear enough.
It's just that when a DLP is placed side-by-side with an LCD, the LCD typically looks a little
bit sharper in comparison. However, it isn't something you'd notice except in a side-by-side
comparison.
A third benefit of LCD is that it is more light-efficient. LCD projectors 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 - there are now DLP projectors rated at 2000 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 in the 15 lb weight class putting out 3000 ANSI
lumens or more are LCD projectors.
The Advantages of DLP Technology
There are several unique benefits that are derived from DLP technology. One of the most obvious
is package size. 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 six pounds and up.
Another DLP advantage is that it can produce smooth, high contrast video. DLP has been well-received
in the home theater world primarily due to two video quality advantages - better contrast and the lack
of pixelation. Earlier generations of LCD projectors were notorious for their inability to generate
acceptable black levels and contrast, and to resolve subtle shadow details. Blacks on LCDs looked
gray and shadows appeared muddy and indistinct. In comparison, DLP projectors did a much better job.
While both technologies have produced improvements in contrast in the past year, DLP projectors
still tend to outperform LCDs in this regard. However the practical performance advantage in black
levels and contrast that DLP holds over LCD has been reduced somewhat. Sony's newly released
VPL-VW12HT carries a manufacturer's spec of 1000:1 contrast, and Sanyo's new PLV-70 is rated at
900:1. Meanwhile, the latest DLP products geared toward home theater are rated has high as 1800:1.
However, one should not place too much emphasis on the specs. In reality, though the difference
between projectors rated at 400:1 vs. 800:1 is quite noticeable, the difference is not so dramatic
between products rated at 900:1 vs. 1800:1. Once you get to contrast ranges of 900:1 or higher,
blacks appear as solid black and shadow details resolve quite nicely. Increased contrast can yield
relatively subtle improvements, but there are other factors which contribute to image quality that
become equally if not more important.
Reduced pixelation is another benefit of DLP. LCDs were always known for their visible pixel
structure, often referred to as the screendoor effect because it appears as though the picture
is being viewed through a screendoor. Historically, LCD technology has had a hard time being
taken seriously among many home theater enthusiasts (quite understandably) because of this
flaw in the image.
DLP technology went a long way toward eliminating the screendoor effect. In SVGA (800x600)
resolution, DLP projectors have either a muted pixel structure or an invisible pixel structure
depending upon the size of the projected image relative to the viewing distance (the larger the
image the more visible the pixels). Conversely, SVGA-resolution LCD projectors uniformly have a
clearly visible pixel grid at just about any screen image size. For this reason, we don't recommend
SVGA-resolution LCD projectors for home theater use except for those on the most limited of budgets.
Three developments have served to close the gap between DLP and LCD in the area of pixel visibility.
First was the step up to XGA resolution (1,024x768). This higher resolution uses 64% more pixels to
paint the image on the screen, as compared to an SVGA-resolution projector. The inter-pixel gaps
are reduced in XGA resolution, so pixels are more dense and less visible. In XGA resolution, DLP
projectors have an invisible pixel grid on any typical home theater screen no matter how big. LCD
projectors with standard XGA panels still have a visible, but much reduced screendoor effect.
Second, the inter-pixel gaps on all LCD machines, no matter what resolution, are reduced compared
to what they use to be. So even the inexpensive SVGA-resolution LCD projectors have less screendoor
effect than they used to.
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. So visible pixel structure is diminished to the point where
it almost as good as DLP, but not quite.
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.
LCD technology has made notable improvements in contrast over earlier generation machines. The
latest products from Sanyo and Sony demonstrate that LCD technology is fully capable of producing
beautiful high-contrast video images. Nevertheless, DLP maintains its lead in contrast performance,
while LCD projector makers have continued to emphasize latent advantages in color fidelity and image
sharpness for data display.
DLP color has improved of late, and color accuracy on the latest models is much better than it
used to be. Marantz in particular has done some remarkable work in getting outstanding color
from DLP with its 12S1 home theater product.
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.
When it comes to home theater, DLP has continued to make competitive advances in color, contrast,
and image stability that have served to establish DLP as the preferred technology for video. But
the fact is that both DLP and LCD continue to improve, and both are capable of delivering higher
quality video for home theater than they ever were before.
Which technology is the best? When comparing DLP to LCD in a home theater environment DLP is the
winner. Better blacks and the removal of the screendoor effect making the DLP an obvious choice.
When you enter in DILA / LCOS technology, is gets more confusing. The native 16x9 panel of the
DLP’s have advantages over the 4:3 DILA panels unless you use expensive anamorphic lenses to harness
its benefit along with hush boxes to quite the noise of the DILA fans. Next, the default contrast and
black levels are poor in comparison to DLP unless you have it sent in to be calibrated. Calibration,
hush boxes, and lenses add a lot of hassle and costs to the final product.
