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One of the great mysteries of the world in which we live,is light.we still do not know exactly what it is. It can only be described in terms of what it does.

We know light is a form of energy. Like some other forms of energy-heat,radio waves and xrays- the speed,frequency and length of its waves can be measured.we know the speed of light.it travels about 186,000 miles per second.This means that in a year, a beam of light travel 5,880,000,000,000 miles.That is the distance which astronomers call a “light year”, and it’s the unit used to measure distances in outer space.

In trying to understand what light is and how it travels, many theories have been developed.In the seventeenth century, Sir Isaac Newton said that light must be made up of “corpusules”, somewhat like tiny bullets shot from light source. But this corpusular theory of light couldn’t explain many of the ways in which light behaves.

At about the same time, a man named Christian Huygens developed a “wave theory” of light. His idea was a luminous particle started pulses, or waves,much as a pebble dropped into a pool make waves.

Wether light is waves or corpusules was argued for nearly 150 years.Gradually,as certain effects of light became known , the idea of light corpusules died out.Scientists now believe that light behaves both as particle and as waves. Experiments can show either idea to be true.So we simply cannot give a complete answer to “What is Light?”.