Education
Projecting the Light
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The first efficient projector, called a 'catoptric' system, was designedby William Hutchinson in 1763. He took a large metal bowl and embedded it with small pieces of mirrored glass. The light source was placed at the focal point of the bowl. The light was then reflected from the bowl and projected outwards as a parallel beam of light. In 1822, the French physicist, Augustin Fresnel, designed an improved projector made from a panel with a central lens surrounded by concentric rings of glass prisms; this gave a concentrated beam of light. He took a number of these panels, mounted them around an oil wick burner on a revolving carriage and so created the first flashing light. A further refinement to his design was the addition of separate rings of prisms to collect all of the light spreading out from the light source. This is basically the system used today which can project a beam that is visible up to 28 miles out to sea. Notes for Pupils Notes for Teachers |
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