Light Has Mass
Light consists of photons. Photons travel at the speed of light (obviously!), and because of Einstein’s Theory Of Relativity, a photon cannot have any rest mass, because that would make its moving mass infinite.
However, I believe that is not quite the case. And I am arguing an alternative, for which some very first, sketchy thoughts can be found on Theorem 1 Draft and Theorem 2 Draft and Theorem 3 Draft. Much more work has been done, and there will be better postings soon. Some second thoughts are at Light Speed (Preliminary) and Light Speed Uncertainty (TWO) and Light Speed Uncertainty (THREE).