Light does not have mass. Light, like sound and heat, is energy rather than matter; only matter has mass. Light is capable of movement and has velocity.
Light behaves as both a wave and a particle. The unit of light is a discrete bundle of energy called a photon. Despite having no mass, photons are constantly in motion and have a constant velocity. In a vacuum, photons move at 299,792,458 meters per second, the speed of light. In other mediums, such as water, photons travel more slowly. Viewing an object through a glass of water leads to the object appearing bent because photons have different speeds in air and water. Unlike matter, photons can be created and destroyed by radiation.