From an old friend in Malaysia, the best explanation of Deepavali. Light to all!
Deepavali the Festival of Light
Deepavali / Diwali is a combination of two names, Dipa, which means lamp and Awali, which means row or line. So in essence, this festival is referred to as the festival of the row of lights. It is widely celebrated wherever Hindus can be found. It is marked by exploding lights, fireworks and so forth. Hindus celebrate it to mark the triumph of light over darkness.
In Sanskrit, light means good and darkness means evil. Therefore, this is a celebration of good overcoming evil.
Happy Deepavali to all who yearn for light to wipe out darkness!