Contrast is what gives depth to the image and determines whether real blacks and whites can be displayed. In fact, that's what contrast is - the ratio between the values of the blackest and the whitest areas. In the jungle of projectors, contrast level values are a particularly thorny area. Manufacturers claim ratios of between 600:1 and 2500:1, but most of the time these values don't hold up under test procedures. Remember that pure black is the sworn enemy of all LCD, DLP, and D-ILA projectors. Only the old tri-tube projectors avoid the problem, but their size and complexity of adjustment quickly put them out of the running with the arrival of the new DLP and LCD projectors.
Due to its very technology, LCD performs worst in the category. Don't think this means you should rule out buying an LCD projector, but do understand that LCDs can't totally block light. So it's hard to get deep blacks without compromising on brightness in scenes with low light, for example. The black of a tri-LCD will at best be a very dark gray that resembles black to the naked eye. But in a dark room, the quality of the image will be quite sufficient. Today's best models offer very satisfactory results for those contemplating the purchase of an LCD. As for DLP and D-ILA projectors, the level of contrast is higher for design reasons. The technology used lets the projector block almost all light emitted by the lamp. This results in a clear improvement in image quality.