The Light Particle is a minor alter ego of Calvin's featured among the Transmogrifier Gun alter egos of the second Transmogrifier Gun story arc. It was not actually featured, but was mentioned by Calvin later on.
Calvin came into this form when his safe deposit alter ego somehow managed to use the Transmogrifier Gun. As such, turning into a light particle may have been Calvin's original intention when he inadvertently turned into the safe deposit.