When it's over we Google around for an answer. It's Diwali (also called Deepavali):
Known as the "Festival of Lights," it symbolizes the victory of good over evil, and lamps are lit as a sign of celebration and hope for humankind....Excellent!
Hindus and Sikhs alike regard it as a celebration of life and use the occasion to strengthen family and social relationships. For Hindus it is one of the most important festivals, and beginning of the year in some Hindu calendars. There are several beliefs regarding the origin of the holiday. The most repeated version is that Hindus celebrate Diwali to mark the time when Lord Rama achieved victory over Ravana. Some also view it as the day Krishna defeated the demon Narakasura or in honor of the day Bali went to rule the nether-world, obeying the order of Vishnu. It is also a significant festival for the Sikh faith. In India, Diwali is now considered to be more of a national festival, and the aesthetic aspect of the festival is enjoyed by most Indians regardless of faith.