Video Projectors

Getting the Right Technology

Three video projector technologies now dominate the home theater market:

LCD Projectors

Well-established in the marketplace, LCD Projectors share many of the advantages and limitations of LCD flat-panel TVs—high brightness capability and low cost, but with limited contrast range and relatively poor color saturation.

Because of their high light output capability, and relatively low cost, LCD projectors are widely used in commercial applications such as schools and businesses—for power point presentations, for example, where the room lighting cannot be turned down completely if viewers are to see the presenter and take notes.

Lower light output LCD models are also available. While often marketed for “home theater” use, they tend to produce disappointing picture contrast and color saturation. But the better ones do provide somewhat high resolution plus high light output—at reasonable cost.

DLP Projectors

They create an image by employing an array of movable micro-mirrors. While producing lower light output than many LCD models, they typically display higher contrast and richer (and more accurate) colors.

Entry level models use a single DLP chip which produces partial (red-then green-and then-blue) image components sequentially. A color wheel spinning in front of the light beam—which is synchronized to the sequential output of the chips—then “assembles” the color components into a full color display, which is projected onto the screen.

Unfortunately, some viewers see distracting color fringing when watching images from single-chip DLP projectors. This is experienced as rainbows in their peripheral vision, and can be very distracting.

High performance DLP models employ three micro-chips—one for each of the red, green, and blue color components—then uses a prism to simultaneously combine the three partial images to project full-color images. These projectors can generate a much brighter image than the single-chip models—without the color fringing.

LCOS (or D-ILA) Projectors

While employing a reflective micro-array similar to the DLP technology, LCOS projectors use liquid crystals instead of mirrors to form the actual pixel display. The result is a rich cinematic image, with high contrast and resolution.

This technology also allows closer spacing between the pixel elements that make up the digital display—yielding a more analog look than the other technologies. This is important when viewing the screen from a close distance.

LCOS light output (brightness) is typically lower than for DLP and LCD projectors. This means that the viewing room must be darkened for best results—fine for cinema buffs who want an immersive movie theater experience, but not ideal for watching sports with friends who are passing along beers and popcorn—or for commercial use.

An Improved Light Source

A new LED light source has entered the marketplace, and is being used instead of the traditional incandescent lamp inside many projectors— helping to provide a more color-neutral image. LED lamps also use much less energy and last much longer than the conventional incandescent bulbs. For these reasons, manufacturers have begun to sell projector models with LED lamps inside.

Unfortunately, this upgrade is not a consumer retrofit project, as the projector must be specifically designed for an LED light source. Hopefully, manufacturers won’t rename these new light-sourced projectors “LED.” If so, it will only add to the confusion—because in this case LED refers only to the light source, not the imaging technology.

The Lens Range

The focal length of the projector’s lens determines how far away the projector must be mounted from the screen in order to fill it with a complete image. A short focal length lens will require that the projector be mounted close to the screen, whereas a projector with a long focal length lens must be mounted far away. A zoom lens (with an adjustable focal length) allows flexibility in mounting distance.

Also new to the marketplace are projectors that are mounted inside an equipment cabinet, which is placed directly in front of (and below) the projector screen. This approach vastly simplifies the installation of the projector system, since the wiring for the video signal and 110 v power is typically located right inside the cabinet. This eliminates the need to run wiring to a distant location, typically in the ceiling opposite the screen, and then mount the projector to the ceiling. But this location is not available in all room layouts.