Several factors should be considered when choosing the right projector for your needs. The most important are Brightness, Resolution, Contrast Ratio and Weight. Here is a general explanation of these key elements.
1. Brightness: Measured in lumens, the higher the lumens, the brighter the projected image. The more light you have in a room when using the projector, the more lumens you'll need. A dark room requires less lumen from a projector. Most projectors project at least 1000 to 1200 lumens. This is usually adequate for dark rooms. However, if you expect light (perhaps notes need to be taken or blinds cannot be closed all the way), consider a projector that provides greater than 1200 lumens. Most professional presenters tend to stay along the lines of 1800 lumens and greater. You should also realize that larger images need more lumens to project clear images.
2. Resolution: This is similar to resolutions offered by computer monitors. The greater the resolution, the more information you can display on a screen. 800 x 600 is usually sufficient for standard presentations that do not require a great deal of detail. However, if you require detail or plan to project images and animations (such as marketing professionals), consider a resolution above 800 x 600. Projectors today typically offer SVGA, XGA and SXGA resolutions. SVGA is usually sufficient for simple presentations. However, for more advanced presentations or larger projected image needs, consider going with at least XGA. For extreme detail, go with SXGA.
3. Contrast ratio: This is a measure of a projectors blackest black and it's whitest white. It basically equates to the brightness of the projector over any room light. There is much debate today over how much the contrast ratio actually affects projected image detail. Some say that anything over 400:1 is pretty irrelevant. However, a good rule of thumb is that if you plan on doing standard, still image presentations without too much detail, then anything over 300:1 really won't make a difference in the overall scheme of things. But if you plan on presenting video presentations with great detail, consider going with a projector that offers a greater contrast ratio. At this time, there is no industry standard of measuring contrast ratio. So a manufacturer that claims a 400:1 contrast ratio may project nicer than another manufacturer claiming the same contrast ratio, given that all other specs are equal.
4. Weight: When purchasing a projector, make sure and choose one that is weighted according to your needs. If you plan on traveling a lot with the unit, choose a lighter projector and consider purchasing a hard roller case for protection and ease of transport.
Other key factors are price and added features such as aspect ratios and wireless capability. If your key usage is home theater, make sure the projector can support a 16:9 aspect ratio so that you can get experience the wide-screen capability of most DVD's. If you plan on using your projector in a room where you want the least amount of "clutter" running from the PC to the projector, consider a wireless capable model. These are just a few of the "extra" features to consider. However, the above listed key elements are generally the most important.
Before you choose your video projector and screen, one practical exercise is to mark out on your wall the size screen you think you might want. You can use black electrician's tape to define the corners of your future screen. Place your seating at the distance you prefer, sit down, and look at the marked out screen area for a while. Imagine action happening in the screen space and get a sense of how much work your eyes need to do to view the image. Work with the image size and viewing distance until you feel it is a comfortable solution for you and anyone else in your household who might be a regular viewer.
Meanwhile, as you experiment with your ideal screen size, there is a second thing to be aware of. The more you enlarge a projector's image and the closer you sit to the screen, the more visible various artifacts become. By the way, the same is true of television. If you view a 2-foot wide television screen from a distance of 2 feet, you will see a blinding mass of scanlines and artifacts. But that same picture viewed from ten feet away looks great. There's nothing different about a projector except the scale.
As a rule of thumb with 720p resolution projectors, a viewing distance of less than 1.5 times the screen width will get you into the trouble zone where pixilation and artifacts become more visibly intrusive. While it is true you have a very BIG image in front of you, these distractions can compromise viewing satisfaction. On the other hand, with the new 1080p resolution projectors, you can sit a bit closer, say at 1.2x the screen width, without worrying about pixilation and artifacts. That still might be too close for comfort from an aesthetic point of view, but some people like to have that very large image in front of them. The 1080p projectors make it easier to do that and still get a clean image.