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Older overhead projectors used a tubular quartz bulb which was mounted above a bowl-shaped polished reflector. However, because the lamp was suspended above and outside the reflector, a large amount of light was cast to the sides inside the projector body that was wasted, thus requiring a higher power lamp for sufficient screen illumination.
Many overhead projectors are used with a flat-panel LCD which, when used this way, is referred to as a spatial light modulator or SLM. Data projectors are often based on some form of SLM in a projection path. An LCD is a transmissive SLM, whereas other technologies such as Texas Instrument's DLP are reflective SLMs. Not all projectors use SLMs ...
Overhead Projectors. Early 1960s-2015 Big metal boxes with glass tops and protruding upper appendages called overhead projectors once did the heavy lifting at corporate meetings, in classrooms, at ...
In the late 1950s and early 1960s, overhead projectors began to be widely used in schools and businesses. The first overhead projector was used for police identification work. [citation needed] It used a celluloid roll over a 9-inch stage allowing facial characteristics to be rolled across the stage. The United States military in 1940 was the ...
The plant was once used to make copiers and overhead projectors, and the facilities have expanded to focus on the adhesive notepads since 1985. Amazon. Pyrex Glassware.
Overhead projector and slide projector: Video projector: Primarily for continued use of older materials. Some teachers find the overhead projector more convenient for lectures depending on their teaching style. Phonograph and phonograph record: Audio cassette, 8 track tape, CD, digital audio: Used to play older or archived recordings.
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