He also hailed Nitish Kumar's decision of imposing prohibition in the state and urged all political parties and people to back his move.
"Nitish Kumar, his government and the people of Bihar deserve credit for making arrangement on such a large scale for holding the Prakash Utsav," Modi said while addressing the main function in the Darbar Hall of a makeshift gurdwara in a "tent city", set up in historical Gandhi Maidan, in the heart of Patna.
Modi mentioned Nitish Kumar not less than a dozen times during his address to praise him for holding the Prakash Utsav and his decision of total prohibition.
"Nitish Kumar has worked hard, day and night monitoring and personally inspecting preparations for the Prakash Utsav for months. He deserves credit for this mega event," the Prime Minister said.
Modi said such mega Prakash Utsav in Patna will inspire all across the country.
He has termed Nitish Kumar's decision of prohibition a "brave step" for social change. "Taking an initiative for social change is very difficult, but Nitish Kumar has initiated it by enforcing prohibition. All people including political parties should back him for it."
Modi shared stage with Nitish Kumar and was seen talking with him. Modi also released special commemorative stamps on Prakash Utsav.
Earlier in the day, the Prime Minister arrived here in an Indian Air Force aircraft to attend Prakash Utsav, said Senior Superintendent of Police Manu Maharaj.
He was received by Governor Ramnath Kovind and Chief Minister Nitish Kumar.
Modi offered prayers and also served during the "langar".
Punjab Chief Minister Parkash Singh Badal, union ministers Ram Vilas Paswan and Ravi Shankar Prasad and a large number of Sikhs from India and abroad will take part in the event.