You have to be careful when talking about "mass" under relativistic conditions.
Light has mass because it has energy. Energy and mass are equivalent from E=mc^2 (a coiled spring therefore weighs a tiny tiny bit more than the same spring uncoiled). It has no "rest mass" though.
Light has mass because it has energy. Energy and mass are equivalent from E=mc^2 (a coiled spring therefore weighs a tiny tiny bit more than the same spring uncoiled). It has no "rest mass" though.
