Prasanna Lakshmi is one among the eight forms of Goddess Mahalakshmi mentioned in the Hindu scripture Lakshmi Tantram. In this form Goddess Lakshmi is in white colored clothes and appears on the left side of Lord Vishnu. She is four armed and has beeja puram kanak, kalash and padmam or lotus in her hands.
The shlokam dedicated to Prasanna Lakshmi in Lakshmi Tantra reads like this
Vande Laksmim parshivamayeem shuddhajambundabham
Tejopuram kanakavasanam sarvabhooshojjvalamgeem
Beejapuram kank kalasham hema padam dadhana
Maadyam Shakti sakalajananee vishuvamamk samstham
Tejopuram kanakavasanam sarvabhooshojjvalamgeem
Beejapuram kank kalasham hema padam dadhana
Maadyam Shakti sakalajananee vishuvamamk samstham
The image of Prasanna Lakshmi is worshipped along with other forms of Goddess Laxmi. This is form is very rarely worshipped as an independent deity.
Please note that Prasanna Lakshmi is not counted among the popular Ashta Lakshmi forms of Goddess Laxmi.