How and Why LCD Projectors Work

A DIY Projector uses a small, bright, white light source, a transmissive LCD panel, and a large format objective lens to project a motion image from your DVD player, video game console, or cable box onto a projection screen. Image sizes range to nearly every end of the spectrum starting at about 40" and stretching to a typical 100" diagonal screen size, though technically you can go to an infinitely large projection size.

How a DIY Projector Works
Every LCD Projector follows a basic design. That is, all LCD Projectors must have at least a few basic components:

• Light Source

• Fresnel Lens

• LCD Panel

• Projection Lens

The diagram to the right shows this generic setup. The key to building a quality projector is to use the best quality components. If any one of these four basic components is of poor quality, the overall quality of your projection will suffer as well.

In a typical LCD projector, a fresnel lens pushes rays of light from a bright light source, through an LCD panel and onto the back of an objective lens (also termed a "projection lens"). The projection lens then focuses the image of the LCD panel onto your wall or projection screen at magnification.

Improving Quality
Here is the main focus of nearly every DIY projector website - how do I improve the quality of my projector? The answer is both simple and complex at the same time. First, the simple stuff. In the most basic terms possible:

1. Use high quality optics (projection lens) for a high quality reproduction of your image.

2. A brighter light source = a brighter projection.

3. The higher quality your LCD is, the more realistic your projection will appear.

Those are the "easy" ways to improve quality. In fact, you can get some of the best lighting and lenses right here at DIY Labs in our parts store to get the best quality possible from your projector. Other enhancements and the reasons why certain types of parts (especially light sources) work better than others, take a look at the other theory pages.

Advanced Design For More Efficient Projectors

Though the above basic design works well, there are many places for improvement. The most basic way to improve this design is to add mirrors between the light source and fresnel lens so that the light isn't shooting in a straight line anymore. This is known as building a "folded enclosure". By doing so, the projector becomes much shorter, though a little bit wider. Overall, the volume of the projector is decreased significantly. The same enhancement can be made between the LCD and projection lens for even more space savings. While either one of these mirrors will greatly decrease the size of the projector, adding the second mirror often doesn't save as much space.

Other enhancements include the use of special combinations of particular light sources, LCDs, and lenses so that even more mirrors can be used. In a modern OTC ("Over The Counter") projector, the light is often "folded" by as many as 3 mirrors before striking the LCD it was meant for. But this is only possible by using smaller LCD panels and very precise reflectors. Our level of precision isn't that high, which is why DIY projectors remain larger than nearly all OTC projectors.

© 2006 DIY For Life Inc