[davidm]

The difference between light waves and sound waves is this: sound requires a medium to carry it; sound waves are a pattern on the substance conveying it. Light, however, does not require a medium; that's why light can travel through a vacuum and sound cannot. Light also displays wave-like and particle-like behavior, depending on what one looks for; this is from quantum physics, and rather mysterious, but the actual effects of light on the eye are well understood, some shatterpot's protests to the contrary notwithstanding.