LCD and DLP each have unique advantages over the other,
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.
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.
LCD Projector Display
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 or Digital Mirror Device
(DMD) chip that has thousands of tiny mirrors, each representing a single
pixel. 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.
One chip DLP
In very expensive DLP projectors, there are
three separate DLP chips, one each for red, green, and blue. However, in
DLP projectors under $20,000, there is only one chip. In order to define
colour, there is a colour wheel that consists of red, green, blue, and
sometimes white filters. This wheel spins between the lamp and the DLP
chip and alternates the colour of the light hitting the chip from red to
green to blue. The mirrors turn on and off based upon how much of each
colour 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.
Three chip DLP
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 colour channel
individually. In LCD projectors with good controls on board, this can
enable the projector to achieve very good, and sometimes excellent colour
fidelity. In most single-chip DLP projectors, colour is fixed and defined
to a large degree by the physical colour wheel and the colour temperature of
the lamp which changes over its usable life. So while DLP technology has
gotten much better at reproducing accurate colour, 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.
LCDs are known to produce greater colour definition, offering more shades or variations of colour than single-chip DLP projectors. DLP projectors can sometimes burn definition out of the highlights and shadows with their vibrant colours.
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
mini-projectors 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
theatre 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 grey
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. Toshiba’s TLP-X4100U LCD projector has a contrast rated
at 800:1. Meanwhile, the latest DLP products geared toward home theatre
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 theatre 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 theatre 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
Competition has driven both the LCD makers and
Texas Instruments (DLP) 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 with LCD
technology are 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 colour fidelity and image sharpness for data display.
DLP colour has improved of late, and colour
accuracy on the latest models is much better than it used to be.
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 theatre.
For mobile presentation it is hard to beat the
current group of 3-pound DLPs on the market even though it is clear that
LCD is still a very strong contender in the mobile presentation market.
And for conference rooms that require higher light output and greater
connectivity, LCD technology holds a lead.
When it comes to home theatre, DLP has
continued to make competitive advances in colour, 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 theatre than
they ever were before.
Which technology is the best? Well, it all depends on your application--both technologies have advantages and disadvantages. Understanding the differences between them will help you select the right solution for your particular needs.
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