Light is weird.

[Kaga]

Ok, so, I'm in my room, no real lights on besides the light coming from my laptop, and I'm just sitting around watching Youtube videos and occasionally checking Spam.

And my laptop has a charger (whom you may remember as the accessory of my fez-wearing bedside lamp) which has a small light on the end of it that attaches to the computer. When plugged in, this light comes on orange, and then it turns green when the system is finished charging.

And so while I'm derping around on Youtube, I'm idly holding my thumb over that charger light and I notice that, in the dark, the orange light essentially shines through my thumb and kind of makes it look like my thumb is glowing.

Mildly amused by this, I sort of kept my thumb there on-and-off for a while before I realized that the light had turned green, as it does when I'm finished charging.

But what made me notice this (at least initially) was not the presence of green light but of no light at all as, once the light changed color, none of it shined through my flesh at all. My thumb was enough to totally block the light.

Which is kind of crazy, since the light didn't appear to change in intensity at all - only color.

Man, light is weird.

[Overwatch]

Different light colors (spectrums), and the light with them get absorbed by different materials. It's what affects how we see colors of various things, such as your skin. Hence your skin absorbs the green spectrums with it's pigments, while not the orange.... I dunno if I'm explaining it right, but, I think that's the way it works.

[Raxacoricofallapatorius]

The thing I appreciate most about light is how Griffin uses it to formulate the theory for his invisibility in The Invisible Man. Hang on, lemme see if I can dig it up.

Here it is:

Excerpt from The Invisible Man that took me a long time to transcribe

"…You know I dropped medicine and took up physics? No!--well, I did. Light fascinated me.

"Optical density! The whole subject is a network of riddles--a network with solutions glimmering elusively through. And being but two and twenty and full of enthusiasm, I said 'I will devote my life to this. This is worth while.'

"I went to work. And I had hardly worked and thought about the matter six months before light cam through one of the meshes suddenly--blindingly! I found a general principle of pigments and refraction,--a formula, a geometrical expression involving four dimensions… But this was not a method, it was an idea, that might lead to a method by which it would be possible, without changing any other property of matter,--except, in some instances, colours,--to lower the refractive index of a substance, solid or liquid, to that of air--so far as practical purposes are concerned."
…
"Visibility depends on the action of the visible bodies on light. Either a body absorbs light, or it reflects or refracts it, or does all these things. If it neither reflects nor refracts nor absorbs light, it cannot of itself be visible. You see an opaque red box, for instance, because the colour absorbs some of the light and reflects the rest, all the red part of the light, to you. If it did not absorb any particular part of the light, but reflected it all, then it would be a shining white box. Silver! A diamond box would neither absorb much of the light nor reflect much from the general surface, but just here and there where the surfaces were favourable the light would be reflected and refracted, so that you would get a brilliant appearance of flashing reflections and translucencies,--a sort of skeleton of light. A glass box would not be so brilliant, not so clearly visible, as a diamond box, because there would be less refraction and reflection. See that? From certain points of view you would see quite clearly through it. Some kinds of glass would be more visible than others, a box of flint glass would be brighter than a box of ordinary window glass. A box of very thin common glass would be hard to see in bad light, because it would absorb hardly any light and refract and reflect very little. And if you put a sheet of common white glass in water, still more if you put it in some denser liquid than water, would vanish almost altogether, because light passing from water to glass is only slightly refracted or reflected or indeed affected in any way. It is almost as invisible as a jet of coal gas or hydrogen is in air. And for precisely the saw reason!"
…
"And here is another fact you will know to be true. If a sheet of glass is smashed and beaten into a powder, it becomes much more visible while it is in the air; it becomes at last an opaque white powder. This is because the powdering multiplies the surfaces of the glass at which refraction and reflection occur… But if the white powdered glass is put into water, it forthwith vanishes… And if you will consider only a second, you will see also that the powder of glass might be made to vanish in air, if its refractive index could be made the same as that of air."

"Yes, yes," said Kemp [the guy he's explaining this all to, and our resident skeptic]. "But a man's not powdered glass!"

"No," said Griffin. "He's more transparent!"

"Nonsense!"

"That from a doctor! How one forgets! Have you already forgotten your physics, in ten years? Just think of all the things that are transparent and seen not to be so. Paper, for instance, is made up of transparent fibres, and it is white and opaque only for the same reason that a powder of glass is white and opaque. Oil white paper, fill up the intersects between the particles with oil so that there is not longer refraction or reflection except at the surfaces, and it becomes as transparent as glass. And not only paper, but cotton fibre, linen fibre, wool fibre, woody fibre, and bone, Kemp, flesh, Kemp, hair, Kemp, nails and nerves, Kemp, in fact the whole fabric of a man except except the red of his blood and the black pigment of his hair, are all made up of transparent, colourless tissue. So little surfaces to make us visible one to the other. For the most part the fibres of a living creature are no more opaque than water."

So yeah, classic science-fiction, but it's cool to think that we're actually doing that sort of thing today. Not turning people invisible, mind you, but the opacity and visibility of objects can be changed at will, like smart glass and stuff.

Great book if you haven't read it.