LCD v DLP - LCD Technology is where the light from the lamp is filtered through red, blue and yellow LCD panels to produce a full colour image. Having three panels means that although still portable, the projector casing needs to accommodate more room for the electronics, making the projector larger. DLP converts light straight into a full colour image, allowing manufacturers to make much smaller projectors. The downside is that the accuracy of the colours produced is not as accurate as many LCD projectors. If colour accuracy is really important to you, we suggest going for a slightly bigger LCD projector.

Lumens (Brightness) - Brightness is measured in 'ANSI Lumens'. Most modern projectors are around 1500 lumens or above, which is more than adequate for the average classroom seating about 20/30 students. However, if there is a lot of ambient light, and you don't want to have to draw the curtains (or if you have a large classroom/Hall) you may opt to go for something nearer 2000/2500 lumens. However , expect to pay a bit more for this luxury!

Resolution - The sharpness and clarity of the picture on the screen is determined by the projector resolution. Resolution is simply the number of pixels (or "picture elements") the projector uses to create the image. Most projectors fall into two categories SVGA (800 x 600 pixels) or XGA (1024 x 768 pixels). Higher resolution projectors are able to show more picture details than low resolution projectors. Also, since there are more pixels used to make the image, each individual pixel is smaller, so the pixels themselves become less visible on the screen. However, you will pay more for the higher resolution.

Contrast Ratio - If you are concerned about picture quality, don't just look at brightness. Contrast is just as important. In short, it's a measure of how well the projector can block out light from the lamp. i.e how black is the black? This is especially important for clarity of text, and in home cinema applications. An average contrast ratio is about 400:1

Lamp Life - Lamplife (normally quoted in hours) is something to be looked at, as this can vary enormously from projector to projector. A standard lamp life is about 2000 hours of projecting, replacement lamps cost between £100 - £300 and sound expensive, but it works out at less than 10p per hour of use. However with all projectors a sharp knock can put the lamp out of action no matter how old it is, so it's prudent to have a spare on hand.

Audio Support - If you are likely to be projecting multi-media with sound, you can either connect your PC to a speaker system, or use the projectors internal speakers. 1 watt mono is about standard for most projectors and is enough for a room of 20-30 students if the only audio is speech. For something more impactful opt for a separate speaker system.

Keystone Correction - "keystoning" is the name given to the effect on the projected image when the projector sits below or above the centre of the screen. Keystone correction counteracts this effect by stretching the image at the bottom or top, resulting in a squarer, more professional image.

Data and Video Inputs - you may want to project from a video player as well as a computer, or have both connected and interchange between the two. If this is the case, check how many data and video inputs the projector has.