3 Different Types of Projectors

3 Different Types of Projectors

The first type I want to discuss is the classic overhead projector. These have been around since 1945 when they where used for training purposes toward the end of World War II. They became popular for use in classrooms in the late 1950s. Overhead projectors are a variety of slide projector. They consist of a large box containing a very bright lamp that is cooled by a fan. On the top of the box is a large Fresnel lens that collimates the light. An attached arm extends above the box and contains a mirror and a lens to project the light onto a wall or screen. Transparencies are placed on top of the lens for display. The lamp technology for the overhead is rather simple compared to the modern LCD or DLP projector. Most use a high powered halogen lamp. These lamps get very hot during use therefore a high flow blower is necessary to keep the lamp from melting itself from the heat output. Because the overhead does not utilize high end technology they are relatively low cost to use. Many classrooms have moved past the classic overhead in favor of the more modern LCD projector. But when budgets are tight, the overhead provides an easy to use, cost effective tool for educators.

The second type of projector is the LCD projector. These use liquid crystal display to project images onto a surface. LCD projectors use glass panels with the liquid crystal between. The video signals are made of three colors, red, green and blue. The crystals open and close to allow light to pass through the glass panels. This creates pixels, which is what produces the image displayed. LCD projectors also use mirrors to split the light from the source into the three colors. The end result is an image with good color saturation. These projectors are most commonly used to display images in a lecture or presentation. Connecting the projector to a computer gives the user the ability to create vivid presentations or show video.

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The third type is a document camera. Document cameras were first developed for the ability to project and present original documents and objects. Many wanted to fore go the prior preparation that is required when using a standard overhead projector with transparencies. A document camera needs an image display device to show the information to the audience. Devices commonly used are a projector, monitor, or a video conferencing system. These cameras allow the user to display an object of artwork, a textbook, or any other original piece of work on a flat surface. Some have exceptional zooming features to give the opportunity to see even the smallest detail of an object. Most have several interfaces provided to allow connections to a computer or interactive whiteboard. Most common are USB, network (LAN) and serial. Also, an external PC or laptop can be easily connected to the document camera to provide the user the option of switching from a power point presentation to a live demonstration. Some document cameras can read external storage devices and play files directly from a USB flash drive.