projector or image projector is an optical device that projects an image (or moving images) onto a surface, commonly a projection screen. Most projectors create an image by shining a light through a small transparent lens, but some newer types of projectors can project the image directly, by using lasers. A virtual retinal display, or retinal projector, is a projector that projects an image directly on the retina instead of using an external projection screen.


There are two common types of projectors: DLP (digital light processing), and LCD (liquid crystal display). In the early days of projectors, CRT (cathode ray tube) projectors were commonly used. They utilized three tubes, one for each of the primary colors. Due to their large size, low light output and the frequent need to converge and align the images projected from each of the three tubes, they are no longer commonly used.


LCD projectors work by utilizing polarized mirrors that pass and reflect only certain colors of light. This causes each channel of red, green and blue to be separated and later re-converged via a prism after passing through an LCD panel that controls the intensity and saturation of each color.


DLP projectors can be classified as one-chip or three-chip. Each chip houses millions of mirrors that reflect light thousands of times each second. One-chip DLP projectors can produce more than 16 million colors while three-chip models can produce more than 35 trillion colors. This allows DLP projectors to reproduce more natural and lifelike images. The closeness of each mirror within a chip makes it difficult to see any spaces separating the pixels and in turn creates a more fluid and crisp image compared to LCD technology. 


Brightness of the projector is rated in lumens. The higher the lumen value, the higher the potential brightness of the image. Projector usage and surroundings determine the type and brightness of projector needed. When used in a small room projecting on a small screen, an LCD or one-chip DLP projector with a lumen rating of 1,500 to 3,000 may be used with appealing results. In large venues using larger screens or when ambient light may affect the image, a three-chip DLP projector with a lumen rating of 10,000 to 28,000 should be used.


Different types of lenses are available. If the projector is to be placed close to the screen, a short-throw lens may be needed. If the projector will be in the back of a room or large arena far away from the screen, a long-throw lens may be necessary. Distance from the projector to the screen and screen size must both be taken into account.