Educational Tool
The overhead projector has been a staple of educational settings for decades. They have grown from being large, cumbersome boxes with loud fans into smaller, more efficient (and expensive) machines that can broadcast from a memory stick.
Tradtional Overhead Projectors
Overhead projectors were efficient educational tools because they had the ability to display a specific sheet of information onto a wall or white screen for a group of people to see. The first ones used en mass were by the army in 1945. Although some police departments had earlier used overhead projectors as a way to display specific facial characteristics, the Army used them in volume as a military training tool. Schools and universities put them into effect by the 1950s and '60s. The way a traditional overhead projector works involves mirrors, bulbs and transparencies. The transparency is a clear, plastic sheet that is usually a copy of a document, such as a set of math problems. The transparency is laid over a light box with a 750-watt light bulb that aims it at a mirror. The mirror reflects the image into another lit mirror, which projects that image onto a wall. With numerous knobs and levers, the overhead projector can be adjusted for better focus.
Modern Overhead Projectors
Although effective, traditional overhead projectors weren't very efficient. The expensive high-heat bulbs could burn out within 100 hours of use. You also had to make sure there was enough room for the overhead projector to fit in the middle of a crowd for better visual projection. The fans designed to keep the bulb cool were also very loud. Modern overhead projectors, known as data projectors, resemble the digital projectors used in movie theatres. They are less cumbersome because they can sit either flat on a tabletop or attached onto a ceiling. Data projectors can translate information from a connected computer or memory stick and project it straight onto a wall or white surface. They also use arc lamp bulbs that are also expensive but are much smaller and last longer. Some data projectors are even equipped to play sounds that could be linked to a presentation. The higher-end projectors are also HDTV ready.
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