Are talking about phonons in optical branches when you say "light phonon"?A major difference between the sound phonon and the light phonon is the light phonon is travelling at relativistic speeds. It's travelling near the speed of light, not near the speed of sound.
If you do, they may have group velocities even lower than these of the phonons in acoustic branches.
If you mean something else, I would appreciate some reference.
You mean that every piece of solid material glows due to this light?Imagine if I had a crystal - all the atoms being held in place by their electric fields - imagine these fields are made of some kind of elastic and flexible material. If I bob one atom against another, they'll giggle up and down. There will be a little oscillation. That oscillation will not be restricted to those two atoms, it will spread through electric fields of the nearby atoms, and they'll spread it to their neighbours. If it reaches the edge of the crystal, and escapes, it becomes light.
What would be the meaning of "60 Hz light"? You mean an electromagnetic wave with 60 Hz frequency? Or light (visible) modulated with a 60 Hz frequency?Just to say something else - if I pass a sound wave of 60Hz through a wall - the other side of the wall must flutter at 60Hz for the sound to pass into the other room - it has to push and pull the air. I'm not sure, but I wonder would you see a 60Hz light too (I don't mean see - I mean I wonder if it's there)
PS. Is it possible that when you say that photons "become" phonons you may be referring to "polaritons" in a dielectric material (describing the coupling between optical phonons and photons)?