LCD Video Projection: The Facts

The second type of rear-projection television technology to consider is LCD (Liquid Crystal Display) projection (not to be confused with LCD flat panel television). Unlike a CRT projection television, the LCD-based rear projection television is not based on the traditional projection tube. A rear-projection LCD television basically works by passing a powerful light source through a transparent LCD chip made up of individual pixels (which displays the moving video image) and projecting that image through a magnifying lens, to a mirror, which then reflects that image, onto a screen.

Advantages Of LCD Video Projection

1. What makes the LCD projector assembly very practical is that it is compact, since the LCD chip is very small.

One LCD chip is hundreds of times smaller than the three projection tubes needed in CRT-based rear-projection televisions. This means that LCD-based rear-projection televisions can be made a lot thinner and lighter than traditional CRT-based rear-projection sets. Although you can’t hang it on the wall like you can with an LCD flat panel or Plasma Television, you can still save a lot of floor space, and spend less money than you would buying that stylish LCD flat panel or Plasma set. In addition, 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 technology are its high contrast and brightness capability, as well as lower power consumption.

Limitations Of LCD Video Projection

1. A LCD projection television can often times exhibit what is called “the screen door 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 a “screen door”.

2. LCD rear-projection televisions, although appearing to be simpler in construction, due to the use of a small chip, rather than three CRT tubes, are still much more complex to produce than traditional CRT projection televisions. This is due to the higher cost of manufacturing the LCD chips themselves. Thus, LCD-based rear-projection televisions are usually several hundred dollars more than their CRT-based counterparts (with 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 displays an annoying black or white dot on the projected image. Individual pixels cannot be repaired, if one or more pixels burn out, the entire chip has to be replaced.

4. Since LCD chips have a finite number of pixels, signal inputs that have higher resolutions must be scaled to fit the pixel field count of the particular LCD chip. For example, a typical HDTV input format of 1080i needs a native display of 1920×1080 pixels for a one-to-one display of the HDTV image. However, if your LCD chip only has a pixel field of 1024×768, the original HDTV signal must be scaled to fit the 1024×768 pixel count on the LCD chip (in addition the image will also have to be letterboxed to reproduce the correct widescreen aspect ratio). This is where CRT-based rear-projection sets can excel 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 surface.

Variants of LCD

Other variants of LCD video projection technology in use 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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