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.
Digital or Computer-Based
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.