Flat panels sit on top of an OHP, using its light source to transmit the image onto a sheet screen or wall. The advantage over using traditional transparency film is that there's no need to print anything out, because the computer screen is displayed directly onto the sheet screen. Despite their quality inferiority to LCD projectors, flat-panel displays still offer some plus points that make them a good choice in certain circumstances. The most obvious advantage is their portability, as they're significantly smaller and lighter than any type of projector. The dimensions are determined by the size of the screen, but even with a 10.4in.
Achievable resolution is another area where flat panels generally have the advantage.
This makes them a good choice for presentations involving high-definition stills, such as CAD images. Because they're not as complicated as projectors, they're also more reliabile, and they have no consumables, such as lamps, that add to running costs. Despite all these advantages, the flat panel market is in decline. In some ways these two reasons are connected, because the achievable image quality depends to a large extent on the type of OHP the panel is used with. A standard OHP will have low-intensity output of around 1,000 lumens and a lens that's not designed specifically for use with panels.