Front Projection 101

Brightness and Contrast Ratio

The projector industry’s most-abused buzzword, brightness is also the most confusing spec for consumers. That’s for a good reason: brightness may be specified in lumens, ANSI (American National Standards Institute) lumens, foot-lamberts, foot-candles, candelas, or “nits,” whatever that means. A few manufacturers specify brightness according to SMPTE (Society of Motion Picture and Television Engineers) standards. This confusing terminology is maddening, very much like the deceptive and sometimes bogus power ratings that manufactures applied to audio amplifiers and receivers in the 1970s—”peak power,” “dynamic power,” “continuous power,” “music power,” all of them different. The situation became so outrageously ludicrous that the Federal Trade Commission stepped in and established strict standards.

Is brightness measured at the lens or at the screen? At what distance? In the center of the image or averaged over the whole screen? In ambient light or in total darkness? With what type screen? With what sort of tint? How big?

These aren’t trivial questions. For example: the bigger the image, the lower the brightness. Video projectors can cast monstrously large images, but they can also cast small ones. The Optoma H31 mentioned above can cast a perfectly focused image from under 3' diagonally to more than 25'. It’s fairly obvious that its smallest image will be many times brighter than its biggest one. Runco, to its credit, clears up some of the confusion in its spec sheets by listing brightness three different ways.

None of this will be discussed or even understood by sales people in big-box electronics stores. Consumers are right to pursue the brightest projector in their price range, but should know that perceived brightness is relative to ambient light. A projector with a relatively low brightness rating of 500 ANSI lumens, like the Faroudja 1080pHD, can look perfectly good in a dark room. Remember, movies are meant to be seen in the dark. Brightness specs range from about 450 lumens for the Piano HE-3200 to 9000 ANSI lumens for the Runco SC-1—a professional projector costing a quarter-million dollars. Among DLP projectors likely to be used by ordinary mortals with ordinary incomes, brightness typically specs out in the 700–2000 ANSI lumens range—pretty darn bright.

Which leads us to contrast ratio: the difference between a projector’s maximum light output and its black level. LCD projectors often have low contrast ratios, especially those that are basically business-presentation machines. NEC’s $2000 VT670, for example, has a specified contrast ratio of only 400:1, despite a brightness rating of 2100 ANSI lumens. This means it has terrible black level—quite likely, it isn’t capable of black at all, but instead renders all dark image-components as shades of gray. No shadow detail is possible, and a film viewed on such a projector would look completely washed out. The Sony VPL-HS51, on the other hand, is also an LCD, but a radically better one, with a specified 6000:1 contrast ratio. DLPs have good-to-excellent specified contrast ratios; 3000:1 or better is typical.

Connectivity and User-Friendly Features

Suddenly projectors are everywhere—not just in hometheater specialty stores, but also in mass-market discount outlets. Staples, the office supply retailer, has almost a dozen models, most of them hyped as being suitable for home theater. Caveat emptor: A close look reveals that most have a skimpy array of inputs—no componentvideo, for example—and unimpressive specifications. If you’re serious about movies, your projector must have a HDMI port and inputs for analog component video. Anything less is unacceptable.

In fact, with the increasing availability of high-def content— TV and, soon, film—it makes no sense for many people to buy a projector that doesn’t have an HD pixel count. Look for a minimum of 1280x720 pixels, and an HDMI interface with HDCP-compatibilty (High-bandwidth Digital Content Protection). HDMI carries high-definition video and multichannel digital audio over a single cable, and the video portion is backward-compatible with DVI via a simple breakout cable. HDCP-compatibility insures that you’ll have a picture with copy-protected sources in the future such as HD set-top boxes and highdefinition optical-disc players.

DVI and HDMI both enable a pure digital signal path from source to projector that is theoretically better than a three-cable analog component input. But theory and reality are frequently at odds. As Shane Buettner and I found out testing the Optoma H31, the best performance was via analog component, with the DVD player in interlaced mode. So it’s important to experiment with various interfaces and settings in both source and projector to find the best synergy. A robust array of inputs on the projector is essential. Projectors come gussied up with many features that may prove convenient during setup but will rarely be used after that—remote-controlled zoom and focus, for example. Inexpensive projectors cost less in part because they give you manual versions of these features on the assumption that you’ll put the projector in one spot, tweak it as needed, and leave it there. On the other hand, some remote setup features are truly indispensable, such as digital lens shift and horizontal and vertical keystone correction (which let you position the projector off-center from the screen and still get a rectangular image), or independent gamma, color, brightness, and contrast adjustments for each input. Chances are, even if your primary purpose is watching movies, you’ll also look at some TV with your projector, and it’s nice to be able to optimize it for both sources.