Clear and Transparent

Recently I learned why light goes through glass and prescription lenses. For that matter, why light goes through water or some other materials that are clear and transparent. I never thought about it before and don’t recall being told this in optometry school where optics seemed like half the curriculum.

It’s simple. Light is a bunch of photons. You could just use those two words interchangeably for this explanation. These photons have a certain amount of energy, right? I shine light in my patients eyes and I know they feel it, some more than others (that’s another story). So this energy that the photons have is enough energy to get us to see and certainly feel by my patients when I turn my equipment on them. How could we see if our eyes weren’t able to detect the photons? So here’s the simple explanation why light goes through some materials (and thus, not our eyes). The photons don’t have enough energy for those materials (specifically the electrons of the atoms that make up the materials) to detect it or it’s not the right amount of energy. Glass is not a good detector for the wavelengths of light that our eyes can detect.

Still, what does “not” the right amount of energy mean? Well, let’s go into some quantum mechanics. It’s not that bad (at least for this little story). You know those electrons are going around in some cloud around the nucleus of an atom, right? Those electrons won’t budge their position if the energy hitting them isn’t enough. Those atoms that make up the materials in our lenses (the ones in our glasses) have electrons that just don’t care when light hits them. I’m not sure if the proper word is hit but maybe it’s more like the photons and electrons weren’t attracted. The light (the photons) just goes right on through the atoms without the least bit of interest from the electrons. There you have it. Quantum mechanics explained in 3 paragraphs!

One more thing about electrons though and you may know this. We get our photons from them. We need atoms and their electrons. When energy goes into an electron it will come back out usually as a photon. There are some finer details about this but for the most part, I’m happy just to know why light goes through the lenses I prescribe to my patients and they are happy whether they know anything about quantum mechanics or not.

Here’s a nice and more in depth explanation:


light going through prism, with reflections as well