JesseG8r

LowRange, light (made of photons) travels through space a constant speed. When photons pass through a medium, such as air, water, glass, or fishing line, however, the photons are absorbed by the molecules within the medium and re-emitted. The amount of time it takes the molecule to absorb and re-emit the photon, and the probability that any given photon will interact with any given molecule dictates the "speed" with which the photons travel through the medium. I put the word "speed" in quotes, because the photons are not actually slowing down (Einstein understood out that the speed of light is constant). The time that we measure when a photon passes through a medium is actually the time that elapses from when the photon is absorbed, and the photon is re-emitted by the molecules it interacts with. When one medium of an irregular shape is immersed in another medium, such as cylindrical fishing line being immersed in water, and the speed that the photons can travel through the fishing line is different that the speed at which they can travel through the water, you will see the prismatic effect you're talking about where the light passing through the line bends. The bigger the difference in speed, the more the light bends, and the more visible the fishing line will be. In the case of fluorocarbon, the speed that photons travel through it is very similar to the speed at which photons travel through water. This makes the light bend very little as it passes from the water into the fluoro and back into the water, and makes the line much less visible than similar diameter monofilament. Fluorokote is a monofilament core with a fluorocarbon coating. Since the coating has similar refractive properties to water, the refraction you see is when it is immersed in water is actually at the border between the monofilament core and the fluorocarbon coating. Since the monofilament core is much thinner than a 100% monofilament fishing line of similar test, it is not as visible.