Reflection is redirecting light by bouncing it off of a surface.
Conventionally we consider reflections off of flat surfaces. (Don't worry about what's about to happen here--it's art!)
Even with reflections off of curved surfaces, each point on it can be considered a locally flat surface.
And more "PBJ" for reflections--they have the curious property of reversing front-to-back symmetry (or here in this perspective, left-to-right symmetry).
Instead of bouncing light off of surfaces, if light can pass into a transparent material, we will have refraction, where it is redirected by being "bent."
Refraction occurs when light starts in one material, and passes into another. (This art installation only gives the illusion of seeing light from people underwater; instead there is only a thin layer of water supported by sheet of glass between these two levels.)
When light does start in one medium, and pass into another medium, it will refract, or bend, which can produce curious results.
Look at the exhaust plume from this jet: heat warms the air and changes its density, making light travel at a different speed through it, and it will be bent in interesting directions. Also note the shockwaves from leading edges on the jet--here air is compressed, and again light traveling through it will be bend it in interesting directions.
Since the index of refraction is a measure of the "optical slowness" of a material, a faster speed of light corresponds to a lower index of refraction, and a larger angle, as it travels into a material with a slower speed, a higher index of refraction, and a smaller angle. Mnemonic: "Fast-to-slow, bend towards the normal."
And since the index of refraction is a measure of the "optical slowness" of a material, a slower speed of light corresponds to a higher index of refraction, and a smaller angle, as it travels into a material with a faster speed, a lower index of refraction, and a larger angle. Mnemonic: "Slow-to-fast, bend away from the normal."