One of the great mysteries of the world in which we live in the light. We still do not know exactly what it is. It can only be described in terms of what it does. We know the light is a form of energy. Like some other forms of energy—heat, radio waves, and X-rays—the speed, frequency, and length of its waves can be measured. Its behavior in other ways makes it similar to these other forms of energy, too.
We know the speed of light. It travels at about 186,000 miles per second. This means that in a year, a beam of light travels 5,880,000,000,000 miles. That is the distance which astronomers call a “light year”, and it is 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 “corpuscles”, somewhat as tiny bullets shot from the light source. But this “corpuscular” theory of light could not 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 that a luminous or lighted particle started pulses or waves, much as a pebble dropped into a pool makes waves.
Whether the light is waves or corpuscles was argued for nearly 150 years. Gradually, as certain effects of light became known, the idea of light corpuscles died out. Scientists now believe that light behaves both as particles and as waves. Experiments can show either idea to be true. So we simply cannot give a complete answer to “What is light?”
What Are The Three Ways Light Travels?
Light can travel in three ways from a source to another location: (1) directly from the source through empty space; (2) through various media; (3) after being reflected from a mirror.