Digital Video Projectors

A video projector takes a video signal and projects the corresponding image on a projection screen using a lens system. A bright light source is behind an image projected through a lens system. A digital video projector sends the light through a medium with a digital image rendered from a digital input source, unlike film, which is an analog medium.

Video projector technologies available:

• CRT
• LCD
• DLP

Projectors with 1,000 ANSI Lumens or greater have sufficient brightness for home theater use. Room size and screen size/distance will affect the need for more or less lumens. Contrast ratios of at least 1,500:1 are good, but 2,000:1 or higher is considered excellent. A native pixel count of 1024x768 is sufficient for DVD, more is required for HDTV.

Lumens: The brightness level (measured in lumens or ANSI-Lumens) is an indication of the level of light thrown out by the projector. This is very important for business presentation projectors.

Contrast: Ratios above 400:1 would not be perceived by the eye if viewing does not take place in a completely darkened environment. So, for the boardroom that is good enough, for the home theater 1500 or above is better.

Resolution: SXGA (1280x1024) is currently the highest resolution available for portable projectors. Common video projector resolutions in the 4:3 aspect ratio are XGA (1024x768 pixels) and SVGA (800x600 pixels).

Video Projector Technologies

CRT Projector (Cathode Ray Tube)

Three small CRTs (one for each primary color), coupled with a light magnifying lens, can project a color image onto a large screen in a darkened room. Best for flexibility of displaying variable resolutions, produce the blackest blacks of all projector types as well as the full range of color, ong projection life (as long as 20,000 hours). Limitations include large bulky size, not very bright, has to be converged properly for best image reproduction, and expensive. Also, limited production now.

LCD Projector (Liquid Crystal Display)

Commonly used for business presentations but with some modification, an LCD projector can provide an excellent option for home theater use. Uses a small LCD screen inside to project light through from a single source.

When using a business-type LCD projector in a home theater setup, the image may appear too harsh with regards to brightness and contrast. As mentioned earlier, the LCD light source (bulb)in an LCD projector must be replaced periodically, depending on the projector, about every 1,000 to 2,000 hours, at a cost of several hundred dollars. A "screen door" grid effect is visible with LCD.

Some LCD variants are LCOS (Liquid Crystal on Silicon), D-ILA (Digital Imaging Light Amplification), and SXRD (Silicon Crystal Reflective Display).

• Low power consumption
• Rich color in rooms that are not dark
• Low heat
• No mechanical color wheel

DLP Projector (Digital Light Processing)

The chip in a DLP projector is referred to as a DMD (Digital Micromirror Device). In essence, every pixel on a DMD chip is a reflective mirror. DLP is good for business presentations and also for home theater. DLP is better for home theater than LCD. DLP is so good that some movie theaters use DLP for feature film projection.

The light source must be changed every 1,000 to 2,000 hours. A "rainbow" effect is visible with DLP on the common single chip model with the spinning wheel. Most DLP projectors use a single monochrome DLP chip and a spinning color filter wheel to generate colors.

• Better video motion
• Unit size smaller
• No screen door grid effect
• Blacker blacks than LCD
• High contrast

There is another group of DLP projectors that uses 3 chips. When you read about DLP you are reading about the single chip type unless the text specifically states "3 chip." These are very expensive, usually in excess of $10K. They do not have the rainbow effect.

Best Application

Some projectors are best for business presentations when connected to a PC while others are best for a television or movie theater type application. Now there are also cross-over' models which can handle both PowerPoint presentations in the office as well as DVD movies at home.

LCD projectors are normally the primary choice with business projectors in view that these still have a brightness edge over DLP.

DLP is still the favored technology when it comes to home theater use due to their improved black level performance and smoother looking projections that resembles more closely those at the movie theater.

SVGA and XGA projectors are more suited for business presentations. XGA projector is the best option for presentations that include graphics or show a web page.

For theater know that most SVGA projectors can display HD video images. The two main HD resolution formats are 1080i (1920 x 1080 pixels) and 720p (1280 x 720 pixels). SVGA projectors, with 800 x 600 pixels of resolution, don't have the ability to display either format without downscaling.

For wide screen movie format the projects that are WVGA or WXGA work. WVGA is the lower end of the two and is fine for DVD movies. WXGA is best for HDTV.