The release of films on Fridays is concept that India has followed from the American style . It is not just in Bollywood, but even the films in regional languages and in the International film industry, the release of new films have been on a Friday.
The first reason that comes to our mind is that Friday is followed by a weekend, a holiday for schools, colleges and offices which means people are more likely to go and catch the last show of the day too.
The finance data of the film industry also shows over the years that this strategy has worked well for the film makers and the distributors in the film industry.Until late 1950's the films were earlier launched even on Mondays and not necessary on a Friday . Super blockbuster film Mughal-E-Azam was one of the first films to be released on a Friday the 5th August 1960 after which the trend in British/ American Legacy was adapted in India as well.
At the time when there were no televisions films continued to be the only entertainment for people, Friday release was planned strategically and majority in the industry also considered Friday the day of the Goddess Lakshmi in India so a release of their new venture came with the belief that producers would be blessed with the good fortune and success for their films.
The producers and directors of the film not only released their films on a Friday but also organised the muharat shots of the films on a Friday which is considered to be an auspicious day to start something new and what most of the sections in India believe in.
The commercial aspect behind this practice was the screening fee that the producers have to play to multiplex owner is much higher on other days then on a Friday.