What is light?

Light rays behave like steams of particles - we call them photons. They also behave as electromagnetic oscillations and we can measure their wavelengths. These range from two fifths to three quarters of a millionth of one metre.

If an object is to be seen it must either emit light, as the sun does, or reflect it from another source, such as the moon reflecting sunlight.

Light is radiant energy emitted by substances excited by other kinds of energy, such as electricity or heat, or by nuclear energy, as in that great nuclear furnace that we call the sun.

Some of the suns radiation could harm us, but most of this is absorbed by our atmosphere before it reaches us.