An LCD projector is a type of video projector for displaying video, images or computer data on a screen or other flat surface. It is a modern analog of the slide projector or overhead projector. To display images, LCD (liquid crystal display) projectors typically send light from a Metal halide lamp through a prism that separates light to three poly silicon panels - one each for the red, green, and blue components of the video signal. As polarized light passes through the panels (combination of polarizer, LCD panel and analyzer), individual pixels can be opened to allow light to pass or closed to block the light. The combination of open and closed pixels can produce a wide range of colors and shades in the projected image.
Metal Halide lamps are used because they output an ideal color temperature and a broad spectrum of color. These lamps also have the ability to produce an extremely large amount of light within a small area: current projectors average about 2,000-15,000 ANSI lumens.
Other technologies, such as DLP and LCOS are also becoming more popular in modestly priced video projection.
Because they use small Metal Halide lamps and the ability to project an image on any flat surface, LCD projectors tend to be smaller and more portable than some other types of projection systems. Even so, the best image quality is found using a blank white, grey, or black (which blocks reflected ambient light) surface, so dedicated projection screens are often used.
Perceived color in a projected image is a factor of both projection surface and projector quality. Since white is more of a neutral color, white surfaces are best suited for natural color tones; as such, white projection surfaces are more common in most business and school presentation environments.
However, darkest black in a projected image is dependent on how dark the screen is. Because of this, some presenters and presentation space planners prefer gray screens, which create higher perceived contrast. The trade-off is that darker backgrounds can throw off color tones. Color problems can sometimes be adjusted through the projector settings, but may not be as accurate as they would on a white background.
What Feature Is Important in Projectors?
Good Optics:
"Optics" refers to the set of mirrors, filters and lenses that transfer the image from within the projector to the screen. The same way that a cheap pair of binoculars can create an ugly view, poor optics within a projector can render blurry or dull images. For example, optics can distort the image, turning straight lines into curves and making sharp edges rough and indistinct. The larger the room and the greater the size of the image, the worse the problems of bad optics. Most projectors have good optics. You can make a quick check by projecting a grid of lines and seeing if they look sharp and straight.
Brightness:
The whole idea of a projector is to convert a small image into a much larger one so that people can see it. It takes a certain amount of light to trigger the sensors in the human eye. That amount changes depending upon the size of the screen and the overall amount of light in the area. To project an eight-foot wide image in a fairly darkened room, a projector would need an output of 1000 lumens, while it would need to output 2000 lumens to project the same size image in a slightly darkened room.
Color Clarity:
When you hook a projector up to your computer screen, you're looking to display exactly what's on your screen. If your computer screen shows a light blue line on a dark blue background, you don't want the projector screen to show purple on a green background. Color fidelity and color clarity are essential to produce a good image. Metrics of color are difficult to come by, so the best evaluation is done by taking an example of the most challenging color image you're likely to need and looking at different projector outputs side-by-side. Your personal taste is the ultimate arbiter of this decision.
Resolution:
Resolution is usually stated in terms of the number of pixels in the horizontal and vertical dimensions. Just remember that higher resolution is not always better. For example, if your computer monitor is a 1024 x 768 pixel screen, sending that image to a 1400 x 1050 projector may actually decrease the image quality. The "extra" pixels are created by interpolating the original pixel values, which tends to blur edges and make a less attractive image. The ideal situation is to match the projector resolution to the screen resolution you need on your computer monitor.
The Rest of the Package:
Most middle- to high-end projectors will have comparable image quality and roughly comparable brightness, so sometimes your selection will be driven by other characteristics. For example, do you need a handheld remote for controlling your projector? Do you want a ceiling-mounted fixed projector or a portable desk projector? Are you going to be toting your projector often enough so that weight is a concern? Consider how you will actually be using your projector to help you decide on the features you need.
