A front-projection system uses a projector and a separate screen, and it projects images onto the front of that screen. This setup looks most like what you'd find in a movie theater - the projection unit is completely separate from the screen. The projector can be placed on a table or mounted to the ceiling. The picture looks best when displayed on a high-quality screen, but a specially painted, flat wall will work as well.

Rear-projection systems look more like traditional televisions. They display images on the back of a screen rather than the front, and the projector is completely contained within the television itself. You can also set up a rear-projection system with a projector and a special screen, but the term is most often used to describe self-contained TV sets.

The transmissive projection types include CRTs and liquid crystal displays (LCDs). Here's a brief overview of how they work:

• One color CRT with red, green and blue phosphors
• One black-and-white CRT and a spinning color wheel that adds the color
• Three CRTs, one each for red, green and blue

Liquid crystal display (LCD):
Electrical currents can cause liquid crystals to change their shape. This allows them to act as light valves - different amounts of current allow different amounts of light to pass through the crystal. This lets the LCD device create a greyscale image. To add color, most projectors use a series of mirrors that split the light into red, green and blue beams. Each beam passes through a separate LCD, and a lens collects the three beams and projects the image on the screen. LCDs can also be used to create flat-panel televisions.