Deepavali (Diwali) is the Hindu Festival of Lights. It is believed that this was the day when good (light) triumphed over evil (darkness). This is why it's a day of celebration and happiness, and Hindu families light small, teardrop-shaped lanterns outside their candles or doorways in order to signify to the spirits that they were a house of goodness.
Today was a happy day. Happy Deepavali!