Light as waves kind of looks like a spring. Mass is a composite concept. There are two masses of relativistic mass and altogether different from restmass. Here is where the 'spring' concept of mass will end this ill-concept of mass and why there are two masses. Replace mass with springs, instead mass is an attribute of springs.
Springs are waves.
Light is a spring and a neutrino is a spring and when a spring is absorbed by another object it has restmass. Thus, an electron has rest mass because it has contained inside of itself many absorbed springs. A photon and a neutrino are thought to have 0 restmass. In the spring theory, all that means is that the photon and neutrino have No absorbed spring. I say no, that the photon has neutrinos inside of itself and at least 2 neutrinos go to compose a photon, thus the spring theory of mass would imply that the photon has restmass.