There are two major categories of Video Projectors: TUBED and Liquid Crystal Projection (LCP)
TUBED or CRT (Cathode Ray Tube) Projectors are the original and, arguably, still offer the best picture.
About: They use three lenses, each on a different axis, that focus separate red, green, and blue images onto a screen. Mechanism is similar to that of a TV.
Commonly used in cinemas and at public displays.
Advantages: Best image, provide big pictures close to the screen (i.e.: 60 inch picture at 2.5m)
Disadvantages: Very expensive, need to be installed by experts, experience is required to use and align the lenses, not easy to move because they are usually fixed assets (mounted to the ceiling or floor).
LCP Projectors are the more user-friendly option.
About: They use a number of liquid crystal panels which are illuminated by a single high-wattage metal halide lamp. A series of filters and reflectors split the spectrally pure white light into rays of red, green, and blue. Each of these beams illuminates a liquid crystal panel and the images from the panels converge at the focal point of a single lens.
Advantages: User-friendly, easy set-up, portable, focus and zoom features.
Disadvantages: The criss-cross network of pixels becomes obvious when the lens is magnified (known as the "chicken wire" effect).
TYPES of Video Projectors
The type of projector refers to the type of display technology used on the projector. LCD's use panels of glass. DLP's use thousands of tiny mirrors.
Standard LCD - These LCD (liquid crystal display) projectors have one panel of LCD glass that controls the three primary colors. These projectors are becoming less common in the projector marketplace, as polysilicon LCD and DLP projectors gain popularity.
Polysilicon LCD - These projectors control colors through three panels and are considered to be of higher quality than standard LCD. The projection through three panels allows polysilicon LCD projectors to have higher color saturation than a standard LCD projector.
DLP - DLP (digital light processing) projectors use a single chip with thousands of micro mirrors to modulate the lamp's light and project it through the lens. DLP systems are composed of over 400,000 tiny mirrors, which modulate light from a lamp and project the "modulated" signal out through the lens onto a screen (this type of technology is also referred to as Digital Mirror Device, or DMD). DLP projectors are one of the more common and newest types of projectors on the market.
LCD and DLP Projector Specifics
Liquid Crystal Display:
LCD projectors are the standard, with polysilicon being of a higher quality than the standard LCD active matrix display. They are normally small and light. They work on similar principles to the LCD computer screen you may be using to read this article.
Digital Light Processing:
These are the up-and-coming technology in the world of projectors. DLP and "Light Valves" are the newest forms of projector technology. DLP's are considered to have brighter images than LCD's, as well as superior video quality. Light Valves are very powerful and bright projectors, and tend to be found on the largest and most expensive models, such as those used in auditoriums and theaters.
LCD vs DLP:
Most multimedia projectors create their images by aiming bright light through small LCD panels containing a grid of thousands of "gates," each of which can be opened or closed to control the brightness and color of light at a given pixel on the screen. Since the panel grid blocks some of the light, this is an inherently inefficient process. However, Digital Light Processing (DLP) eliminated this inefficiency. Instead of LCD panels, DLP relies on small chips that contain arrays of tiny mirrors, which can be moved to control the brightness and color of light at a given pixel. This arrangement allows nearly all of the light output to make it to the screen.
LCD Pro's and Con's
Pro's - offer a bright and sharp picture with vibrant, rich colors
Con's - they have a fixed amount of pixels so when blown up, the pixels may be visible (like viewing through a fly screen, known as the "screen door" effect); dark areas can be a problem too, as blacks become hazy greys and shadow detail is poor.
DLP Pro's and Con's
Pro's - vivid pictures, bright, excellent contrast, less pixilation than LCD's
Con's - the mirrors in the system reflect all light, so it is a challenge to keep the color BLACK dark enough to provide high-contrast images; some people complain that they can see rainbows (colors following movement on the screen) and that their eyes become sore after some time with a DLP projector.
Ensure that you (and any others likely to spend time watching your projector) spend some time looking at the model under consideration for purchase before spending your money.