There are several types of projectors that can be used for presentations or entertainment. A front projection projector is good for large audiences but makes interaction difficult. A rear projection TV projects an image through lenses and mirrors to create a large screen image in a shallow depth. CRT projectors use small color CRT tubes to focus and enlarge the image onto the screen, while LCD projectors send light through a prism to separate colors and display the image. DLP projectors use a digital micro-mirror device to project images. The brightness level in lumens is an important factor, as is the throw distance between the projector and screen. Projector lamps are a key component that transfers the image to the larger screen.