There are several reasons for celebrating Deepawali. The most important one is the commemoration of the return of Lord Ram to Ayodhya after 14 years of exile.
Lakshmi Puja during Diwali is observed as it is believed that Goddess Lakshmi emerged from the ocean on this day during the ‘samudra manthan’ (churning of ocean) by demons and gods as mentioned in the Puranas. So for the business people, the new business year begins on Diwali.
The word Diwali is made of two words; deep (lamp or diyas) & avali (row), which means a line or a row of lamps. During the festival of Diwali lamps are lit in every home, office, etc. that is why this festival is also known as the ‘Festival of Lights’. Diwali is also called as Deepavali.
courtesy : hindu-blog