The Significance of Lights & Firecrackers
All the simple rituals of Diwali have significance and a story to tell. The illumination of homes with lights and the skies with firecrackers is an expression of obeisance to the heavens for the attainment of health, wealth, knowledge, peace and prosperity.
According to one belief, the sound of fire-crackers are an indication of the joy of the people living on earth, making the gods aware of their plentiful state.
Still another possible reason has a more scientific basis: the fumes produced by the crackers kill a lot of insects and mosquitoes, found in plenty after the rains.