Light does not have mass per se. It behaves as a particle or a wave, depending on how and when you measure it. A photon has energy which is in many ways equal to mass (remember an objects energy equals its mass times the speed of light squared), but it does not have actual mass, as it would then be impossible for it move as fast as it does. As a particle it displays many of the behaviors of other massive particles, such as being effected by gravity, but at the same time it's behavior as a wave dissallows it from having mass. Confusing, no?
