Two Lakshmi Pujas are observed within a fortnight in Bengal — Kojagari and Dipanwita: one on the Ashwin full moon, the other on the Kartik new moon. Both take place at night. Outside the month of Kartik, Lakshmi Puja is not performed on any new moon in Bengal.
There are several legends associated with Dipanwita Lakshmi
Puja on Diwali night.
One such story says —
Once, by a king’s decree, the entire kingdom was kept in darkness on Kartik
Amavasya. Riding her owl, Goddess Lakshmi went on her nightly round and found
the world shrouded in darkness. Only in a small hut deep within the forest did
she see a faint glimmer of light. She descended there and found a sorrowful
princess lighting a lamp and weeping in poverty. Pleased with her devotion,
Lakshmi blessed her, and her miseries vanished. Thus arose the tradition of
worshipping Lakshmi on the night of Dipanwita Amavasya.
Another legend tells that once a dispute arose between
Vishnu and Lakshmi over the importance of wealth. Unable to bear the discord,
Lakshmi left Vaikuntha and was born on earth as Princess Padmavati. Without
her, Vaikuntha lost its splendor, so Vishnu too descended to earth, born as a
poor woodcutter living in the forest. The two met again — but Vishnu, in
poverty, could not bring her home. Finally, he borrowed money from Kubera, the
god of wealth. Years passed, yet he could not repay the debt. In the end,
Vishnu surrendered to Lakshmi, who, moved by compassion, released him from
Kubera’s debt.