Overview of
LCD video projection
Info on LCD Video Projection
Liquid Crystal Display (LCD) Projection
I'll describe the second kind of rear-projection TV technology to consider: it's LCD (Liquid Crystal Display)
projection. Don't confuse this with LCD flat panel TVs. Unlike a CRT projection
TV, the LCD rear projection TV is not based on
the traditional projection tube.
A rear-projection LCD TV works by passing a powerful light source through a transparent LCD
chip made up of individual pixels (which display the moving video image) and projecting that image
through a magnifying lens, to a mirror, which then reflects that image, onto a screen.
LCD Video Projection advantages
1. What makes an LCD projector very practical is that it is compact, because the LCD
chip is very small. One LCD chip is hundreds of times smaller than the three projection tubes
needed in CRT rear-projection TVs. This means that LCD rear-projection TVs can be made a lot
thinner and lighter than traditional CRT-based rear-projection sets.
OK, you can't hang it on the wall like you can with an LCD flat panel or Plasma Television, but
you can still save a lot of floor space, and spend less money than you would buying that well
styled LCD flat panel or Plasma set. On top of that, since these are projection sets, you can get
one in larger screen sizes than you can with either LCD or Plasma flat panel types.
2. Other advantages of rear-projection LCD are its high contrast and brightness, as well
as lower power consumption.
LCD Video Projection limitations
1. An LCD projection TV can often times show what is known as "chickenwire effect". Since the screen is made up of individual pixels, the pixels can be visible on
a large screen, thus giving the appearance of viewing the image through "chickenwire".
2. LCD rear-projection TVs, appear to be less complex, due to the use of a small chip,
rather than three CRT tubes. But they are still much more intricate to make than traditional CRT
projection TVs. This is down to the higher cost of manufacturing LCD chips themselves. LCD
rear-projection TVs usually cost more: several hundred pounds more than their CRT counterparts (size and
features being equal).
3. Since an LCD chip is made up of a panel of individual pixels, if one pixel burns out it shows
a really annoying black or white dot on the projected image. Individual pixels can't be repaired. If
one or more pixels burn out, the entire chip must be replaced.
4. Because LCD chips have a limited number of pixels, signal inputs with higher resolutions
must be scaled to fit the pixel field count of the particular LCD chip.
A typical HDTV input format of 1080i needs a native display of 1920x1080 pixels for a one-to-one
display of the HDTV image. But if your LCD chip only has a pixel field of 1024x768, the original HDTV
signal must be scaled to fit the 1024x768 pixel count on the LCD chip. The image will also have to be
letterboxed to reproduce the correct widescreen aspect ratio.
This is where CRT rear-projection sets can score over an LCD rear-projection set. Since CRTs are not
limited by a fixed pixel field, they are more flexible at displaying various resolutions, due to being able
to variably scan the image onto the projection tube.
LCD Variations
Other variations of LCD video projection used are: LCOS (Liquid Crystal on
Silicon), D-ILA (Digital Imaging Light Amplification - developed and used by JVC), and SXRD
(Silicon Crystal Reflective Display - developed and used by Sony).
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