Why does light exist and what is its purpose in the universe?

God had created the sun not only for light but for many other purposes. Human beings and all other creatures cannot survive without sunlight. Water evaporates, change into clouds which cause rain. Sun is energy and life. There are suns in other parts of the universe because they are necessary to keep the other planets and stars in tact in their position. God has created the center of gravity not only to earth but to also to all planets and stars of the universe. If this center of gravity is removed each and every planet will split into several particles and fly high to the sky.

The empty planets which exist in the universe are an evidence to guess that God might have taken many many years to create the earth and human beings. Those empty planets are the remains of His experiments. He might have failed many times before He creates the earth and the creatures.