A basic earthen oil diya used for Diwali
A Diya, divaa, deepa, deepam, or deepak is an oil lamp usually made from clay, with a cotton wick dipped in ghee or vegetable oils.
Clay diyas are often used temporarily as lighting for special occasions, while diyas made of brass are permanent fixtures in homes and temples. Diyas are native to India, and are often used in Hindu, Sikh, Jain and Zoroastrian religious festivals such as Diwali or the Kushti ceremony. A similar lamp called a butter lamp is used in Tibetan Buddhist offerings as well.
Traditional Use 
A diya placed in temples and used to bless worshippers is referred to as an aarti.
See also