Our most important source of light is the Sun. The Sun has an enormous amount of energy which is given out in the form of heat — at its centre, the temperature of the Sun is about 13 million degrees centigrade! It is some of this energy which reaches us as light.
Since the Earth spins around once every 24 hours, we only face the Sun part of the time — the time we call ‘day’. At night, light from the Sun can no longer reach us. But even at night there is some light. The stars, like the Sun, produce light. The Moon also provides light. But the Moon has no light of its own — it simply reflects light which has reached it from the Sun.
Electric lights enable us to see well at night. At night, we see how the Moon reflects the Sun’s light.