There is no Diwali without Diyas or lamps. Diyas are an indispensable part of Deepavali celebrations. But why do we light lamps during Diwali? Legend has it that the tradition of lighting diyas during Diwali began when Sri Ram returned to Ayodhya after completing his 14-year exile. People of Ayodhya wanted to give an extraordinary welcome to Sri Ram and it is said that they lit lamps everywhere in Ayodhya. It must have been a great sight to Sri Ram, who was returning from Lanka in Pushpak Viman – flying machine, to see the Diyas in all of Ayodhya.
Another reason for lighting lamps is that Diwali is observed on Amavasi. The no moon day (Amavasi) which is the darkest day in a Hindu lunar month is also dedicated to dead ancestors. There is also a belief that the period of night time of ancestors begin with Diwali Amavasi. So the lamps are lit to show them way to their abode. This belief is widespread in Eastern parts of
Lighting of lamps on Dhanteras is dedicated to Yama. This is also known Yamadeepdan. The lamps are not put off and burn for the entire night on the day.
People also float lamps in rivers and ponds on Dhanteras day. This is dedicated to dead ancestors.
Symbolically, the Diwali lamps signify the removal of spiritual darkness and self realization - Realizing the Brahman in all animate and inanimate.