Projectors fall into three broad categories: home cinema, business and portable. Projectors designed for home use aren’t usually as bright as office models, as they’re intended for use in a darkened room. Look for at least 1600 ANSI lumens brightness rating, as this should allow you to watch a film with at least one light on – those that have less than 1000 ANSI lumens rating are only really usable in total darkness.

It’s important to understand the difference between the two main projection technologies: LCD and DLP. LCD projectors tend to be larger, but are more likely to have lens-shift than DLP versions. DLP models usually have better contrast and punchier colours, but suffer from the ‘rainbow effect’ where the component colours of the image (typically red, green and blue) become visible. This can be very distracting to more sensitive viewers, and is especially visible in high-contrast or black-and-white scenes.

A projector’s specifications will tell you little about image quality, so if you’re concerned about colour accuracy, contrast and sharpness, make sure you read our reviews which tell you how each model fared in our tests. See also: Group test: what's the best projector?

Home cinema projectors

Cheaper home cinema projectors tend to have a 720p resolution (1280 x 720), which is quite usable, but you’ll notice the extra detail produced by a full-HD 1080p (1920 x 1080) model if you’re watching Blu-ray films on a big (100in+) screen.

If you can’t place your projector square-on to your screen, look for a model with lens shift. This is where the lens can be physically moved to shift the image horizontally and/or vertically, allowing you to place the projector off-centre.

Keystone correction is the poor man’s lens shift, altering the image digitally to correct the aspect, but potenially degrading image quality in the process.

Most projectors also have a zoom, which gives you more flexibility to mount the unit closer – or further away – from your screen. If you have a very small room, look for a short-throw model which can produce a very large image from a short distance.

Motion smoothing is another feature to look for. Virtually all films run at 24 frames per second (fps), and TV broadcasts at 25fps in the UK. When objects move across the screen, or the camera pans left or right, this can appear jerky – especially on huge screens. Motion smoothing intelligently adds extra frames (guessing where objects would appear between the original frames) to produce a far less jerky result.

Office projectors

When choosing a projector for business use, you’ll typically opt for either a portable model or a permanent installation. Regardless of the type, make sure the lamp is bright enough. Under normal fluorescent lighting, you’ll need at least 2000 ANSI lumens, but increase this if you’ll also be competing with sunlight. Plus, don’t forget that the brightness drops as you increase the size of the image.

Portable projectors

Small and lightweight projectors, especially the so-called pico projectors, can be tempting for their very portability. They often use white LEDs for a bulb, making them smaller and cooler-running. But beware that light output is much less than regular models, making them only usable in very dark rooms and/or at short range. Some even run from batteries, although with limited runtime – check our reviews to get an idea of real battery life.

See also: Group test: what's the best projector?