Features to look for when shopping for a projector

These days, the projectors from major manufacturers all look impressive. But of course, each has its own unique strengths and weaknesses, and no single model will be the best choice for all rooms and signal sources. You can get a general idea about how a projector will perform by comparing these three key specifications.

Resolution: For digital projectors, resolution is the number of pixels measured from side to side and top to bottom of the imaging chip. High-definition projectors will have resolutions of 720p or 1080p. Projectors with greater resolution can more accurately reproduce high-resolution signals; because each pixel is smaller, images look more seamless, with less noticeable "pixel structure." A projector's built-in scaler will upconvert or downconvert all incoming signals to precisely match its "native resolution." See our article about HDTV resolution for more info.

Contrast ratio: This measures the difference between the whitest whites and the blackest blacks a projector can show. A higher contrast ratio makes it possible to display deeper blacks and more subtle color detail. Good contrast is critical for home theater projectors. In fact, many models include multiple lamp settings that let you reduce brightness and boost contrast ratio for optimum viewing in a darkened room.

Light output (brightness): Home theater projectors typically have brightness ratings of 700-2500 lumens. All projectors have plenty of brightness for watching movies in a dimly-lit or darkened room. A higher brightness rating will come in handy for viewing when there's more ambient room light. It's also helpful if you're projecting onto a wall (it's less reflective than a screen), or if you're displaying an extra-large image (110" across or larger).

Projectors have the same video inputs you find on most HDTVs, including HDMI and component video for high-def content.

Projector technologies

Many projectors today rely on one of two digital technologies: LCD and LCoS. We've outlined how they each work below.

LCD: It's not just for flat-panel TVs
You're probably familiar with flat-panel LCD screens in TVs and laptop PCs, but LCD technology also lends itself to projection displays.

The 3-panel LCD light engine of a Sony Grand Wega TV. Light from the lamp (left) passes through special "beam-splitting" mirrors. The white light is split into beams of pure red, green, and blue light. Each beam is fed through its own dedicated LCD image panel. The resulting three monochrome images are then combined to form the full-color image, which is projected through the lens.

Liquid crystals are rod-shaped molecules that bend light in response to an electric current. Each crystal acts like a shutter either passing or blocking light; the pattern of transparent and dark crystals forms the image you see.

LCD-based projectors use three high-resolution LCD image chips, one each for red, green and blue. Think of these chips as miniature flat-panel LCDs — each chip contains up to one million pixels, or more, and each pixel is driven by its own transistor and electrical conductors.

Light from the high-powered lamp is split into isolated red, green, and blue beams using special "beam-splitting" mirrors (see illustration, above). Because there's a dedicated LCD panel for each primary color, and color accuracy is excellent. Once the three single-color images are created by the LCD image chips, a prism combines them into a full-color image, which is projected through the lens.

LCoS: A more advanced form of LCD
An LCoS image chip is a complex, multi-layered design. Lots of projector manufacturers have proprietary names for their LCoS technology — for example, Sony's SXRD™. As with an LCD chip, there is a layer of liquid crystal material. But beneath that is a reflective metal layer. As the liquid crystal layer responds to the signal voltage, the molecules shift and align in corresponding patterns to create an image.

The circuitry controlling the crystals' alignment is etched into the silicon base of the chip, so it's out of the way, behind the liquid crystal layer. Light efficiency is higher because the light doesn't have to pass through the drive electronics (as it does in LCD chips). So, for a given amount of light, an LCoS panel will yield a brighter image than an LCD panel.

Most of the models currently available are the more successful 3-chip designs like Sony's SXRD projectors. 3-chip systems (both LCoS and LCD) use an elaborate light path employing "beam-splitters" that divide the light into pure red, green and blue. Each beam shines onto a dedicated image chip. Then the three monochrome images are combined by a prism to form the full-color image, which is then projected through the lens. To see how this process works, check out this short animation.