Projectors receive data from a computer or video source and project this data onto a screen via internal light sources, power sources, and converters. Projectors include electronic devices that display video and computer-based images or presentations and transparency devices that use a light source and lens to project an image from a transparent film medium.
Projectors are commonly used in classrooms and conference rooms for presentations. A slide projector is an opto-electronic projector that uses a light source—usually a fan-cooled light bulb, a reflector, a slide holder, a focusing lens, and a condensing lens. Light from the bulb passes through the transparent slide and focusing lens and the image is projected on a screen or wall. The most common slide projector is a carousel projector that uses a stepper motor to advance the carousel and load the slide into the holder in succession. An overhead projector is also a transparency projector that uses a bright light source and lens to collimate the light. Overhead projectors consist of a flat light box with a mirror attached by a flex arm to the box. The mirror reflects the enlarged image of the transparency on the wall.
Most projectors used today are digital or computer-based projectors. A digital projector is connected to a computer and can project the images or files on the computer screen onto a wall. Digital projectors are differentiated by their resolution, brightness, and the type of projection technology used. An LCD projector uses a liquid crystal display panel for each color of the video signal—red, green, and blue. The LCD panels control the light and the display of the image. Another type of computer projector is a digital light processing (DLP) projector, which uses microscopically small mirrors configured on a microchip. A cathode ray tube (CRT) projector is a type of video projector that uses small separate picture tubes to process the video signal. A lens focuses the video image and projects it on a screen.