The third day of Diwali festival is the most important one for Lakshmi-puja and is entirely devoted to the propitiation of Goddess Lakshmi. On this very day sun enters his second course and passes Libra which is represented by the balance or scale. Hence, this design of Libra is believed to have suggested the balancing of account books and their closing. Despite the fact that this day falls on an amavasya day it is regarded as the most auspicious.

The day of Lakshmi-Puja falls on the dark night of Amavasya. The strains of joyous sounds of bells and drums float from the temples as man is invoking Goddess Laxmi in a wondrous holy “pouring-in” of his heart. All of a sudden that impenetrable darkness is pierced by innumerable rays of light for just a moment and the next moment a blaze of light descends down to earth from heaven as golden-footed Deep-Lakshmi alights on earth in all her celestial glory amidst chantings of Vedic hymns.

A sublime light of knowledge dawns upon humanity and this self enlightenment is expressed through the twinkling lamps that illuminate the palaces of thewealthy as well as the lowly abodes of the poor. It is believed that on this day Lakshmi walks through the green fields and loiters through the bye-lanes and showers her blessings on man for plenty and prosperity.

Lakshmi Pooja, or the worship of the goddess of wealth, is the main event on Diwali in North and West India. It is extremely important to keep the house spotlessly clean and pure on Diwali. Goddess Lakshmi likes cleanliness, and she will visit the cleanest house first. This is also the reason why the broom is worshiped on this day with offerings of haldi and kumkum (turmeric and vermilion). Lamps are lit in the evening to welcome the goddess. They are believed to light up Her path.

Lakshmi Puja consists of a combined puja of five deities: Ganesha is worshiped at the beginning of every auspicious act as Vighnaharta; Goddess Lakshmi is worshiped in her three forms – Mahalakshmi (the goddess of wealth and money), Mahasaraswati (the goddess of books and learning), and Mahakali; Kuber (the treasurer of the gods) is also worshiped.

Source: https://diwalifestival.org/lakshmi-puja-on-diwali.html