Just a point.. Light is electromagnetic radiation, movement of photons, or em waves, or whatever you want to think, travels at 2.998x10^8 m/s and has no mass. Sound is the movement of air particles in longitudinal wave patterns. The molecules in the air hit each other in a sort of domino effect, and sound waves dont actually have substance. Light can exist in a vacuum, sound cannot. The average sound wave moves at 343m/s in air, and faster depending on the medium it is going through. A denser material will allow less "space" before the particles "hit" each other and cause the sound wave, and thus the wave moves faster. They are two completely different phenomena.