 So we can describe light as traveling in more or less straight lines for most purposes, and that lets us design optics, we can describe light as bouncing off mirrors and other things that reflects off at the same angle, pretty much like a ping-pong ball bounces off a wall. But when we add the wave model of light to things, we can understand details like how it makes interference patterns and diffraction patterns, and also let us understand things like the fact that it has polarization, and the fact that it's an electromagnetic wave unifies our idea of not just light, but also x-rays and ultraviolet light and infrared light and television signals and Wi-Fi signals and radio and so forth. And so our model of light has got larger and larger and explained more and more, and various approximations allow us to make simple calculations that are applicable in each realm.