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Lens
In a laser light of a certain colour is shone onto a crystal. It makes the crystal send out more light of exactly the same colour.
If this process is repeated, a very powerful beam of light is produced. The first laser was built in 1960 by Theodore H. Maiman of the United States, using a rod of ruby.
LED
Light-emitting diode. When electricity passes through a special kind of semi-conductor called a diode, the material gives out light. The light given out can be quite powerful. LEDs also have a far longer life than ordinary bulbs. Most indicator lights on electrical equipment are LEDs, while the central brake lights on the rear of new cars are also made from a row of LEDs.
Light source such as flashlight
Lens
A piece of transparent glass, plastic, or crystal that has one or both sides curved in such a way
as to bend the light to make an image. Eyes also contain lenses, but they are flexible and made from flexible fibres. In this way eyes are adjustable lenses.
Lenses are used in cameras, microscopes, projectors and telescopes, as well as eyeglasses and contact lenses.
You can also see lenses at work in the natural world. A raindrop on a leaf or stem will act as a natural enlarger, magnifying the surface it is on. A glass bowl or drinking
glass filled with water will bend light and bring it to a point, or focus.
People began to use lenses to
help with eyesight in the 13th century. The word lens comes from the rounded shape of the
lens, which people thought looked like a lentil (lens in Latin).
The first telescopes were made by lens-makers. Galileo built a telescope of his own in about 1609, using two lenses. At about the same time people began to build microscopes, again using two lenses.
By the 18th century the first lenses were being made that did not produce undesirable colour problems (see: Aberration). They were complex lenses – two or more lenses stuck together to produce better quality.
In 1866 the German optician Ernst Abbe, who worked for Carl Zeiss in Jena, stated the
 Lens – The way curved transparent materials bend the light to bring it to a focus can be shown by this simple demonstration. A number of slits are cut in a piece of paper, and a drinking glass placed in front of them. The rays of light not blocked by the glass continue as parallel beams, while those that go through the glass are brought to a focus. Any curved glass or other transparent object will focus rays in this way, but to be useful, the curved glass needs to be designed with a certain focal length. It is then called a lens.
Teeth cut in card (or comb) used to produce rays from light source
Drinking glass acts as lens and focuses light rays to a point.
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