Amavasya or amaavas is the darkest night of the traditional Hindu calendar. This happens because there is a lunar eclipse on that night and understandably, the moon is hidden from sight. Due to this phenomenon, natural light is almost nil. The festival of Diwali also falls on such a night.
The spiritual significance of Diwali may differ from region to region in India. However, in the Ramayana, Diwali was celebrated to honor the returning of Ram, Sita and Lakshman from their 14 year long exile. Most of the people celebrate Diwali keeping this reason in mind. In a more abstract sense, it is believed that Diwali is the expression of the belief that good will always vanquish evil.
Whatever our reasons for celebrating this festival, it is always important to remember that due to this festival, we light a diya on a moonless night and dispel the darkness. This might not mean much literally in the age of electricity and back up generators. But on a philosophical level, no matter how much negativity and darkness surrounds us, we always have the power to lessen it by being the source of light.
Henceforth when we celebrate Diwali, let us keep this thought in mind. This philosophy is not something that is to be tucked away all year and only be reflected upon during this festival. It is something that if followed, can make us stronger in our day to day lives.