I don't know
why, but I've never really 'understood
, in general. I know all of the details
, how lenses
, diffraction, refraction
, blah blah, but overall I couldn't actually Picture
it very well in my head
. I won't go too deeply into light, there's a lot to it. There's colors
and different reasons different things are different colors. I'm just concerned with light in general here, and that's how I'll treat it. I always had questions like: If light spreads
out the farther away from an object
it gets, then how does perspective
work? Wouldn't it almost seem that objects should look Bigger the farther away from them you are? And I understood how an image gets inverted
through a lens; for those who don't know, I'll explain it briefly. Ever taken a photography
class, and had it explained to you how a image gets inverted through the camera
, and is "upside down
" when the film's developed? Or ever heard about how images come through your retina
, and are actually "upside down" when they get to your brain
? Then it goes that your "brain has to 'flip' it" so that you get experience down as down, and up as up. The camera analogy goes, a lens is curved
so any light passing through the bottom of the lens gets directed "upwards" and any light hitting the top of the lens gets diverted "downwards" kinda like this:
So, since the light that hits the bottom of the lens is directed "up" and vice verse, you get an inverted image on the film.
It's not the best explanation, but I hope you can picture what I mean. So, understanding how a lens flips an image, something still didn't make sense. Pinhole cameras are said to invert images, too. Those are the science project cameras, where you simply get a box, poke a hole in one side, cover the hole, put some film inside the box, and then you uncover the hole for a few seconds, cover it again, develop the film, and you have a picture! But still, there's no lens here, only a hole in a box. What special properties does the hole have that inverts an image when it comes through?
I had all these weird ideas, about how light hitting the edge of the pinhole would "curve around it" kinda like pressurized water going through a small hole, stuff like that. Either way, it just never quite came out right in my head when I tried to picture it.
The first clue to my understanding of light, came when I started to learn about how holograms work. Nobody ever really seemed to be able to exactly explain it to me, but every explanation always had something like "every part of the image, is made up of the whole image" and other odd things like that. This started to make sense to me, if every part of the light reflected off of an object looks like the whole object, I can start to fill in a few of the pictures in my head. That would explain things like: why a star billions of light-years away still looks like a circular star on earth when we're only looking at an extremely tiny, tiny, fraction of the light cast off by that star. But still, how can you picture this "every part of the image looks like the whole image" stuff?
Let me give you an example of why this "every part of the picture is the whole picture" thing was a clue that set me off in the right direction to understanding light. Ever do the classroom projects to view an eclipse through a pinhole? How does that work? Not only that, but have you ever seen the light shining through trees during an eclipse? There's all these little eclipse-shadows on the ground! Ever wonder what was up with that?
To finally understand light, I had to go through a little thought experiment in my head. First, picture some round ball or something. Keep it one color, like a solid red ball. So now you're looking at this ball a few feet away from it, maybe five feet. You can see the ball, it's smooth, it's red, it's round, etc, you're looking straight at it. Now get a little closer to the ball, maybe a foot away. It's bigger now, but it's still smooth, bright, maybe you can catch a little shine from one part of it or something. Now get closer still, maybe an inch away. From here you can't really see the whole ball, only a portion of it. But you can start to see that it's not quite smooth, it has a little bit of texture on it, you can see little hints to small bumps and imperfections it may have. Get closer, still. Now you're looking at it like through a magnifying glass.
You can't see the whole ball, it's a smaller portion even still, filling up your whole vision. With this view, you can see that it's not only a few small bumps, it's a whole lot of tiny little bumps, each one you can see in 3d, like a basketball up close. Closer.
Now you're so close that it's like the view through a powerful microscope. You're only looking at a few of the "bumps" now, but you can almost start to see that these bumps are kind of made up of bumps themselves. Get closer. You're looking at the individual molecules that are making up the ball now. We're not going to get any closer than this to understand light.
So you're looking at these molecules, they still look like small spheres, we're not close enough to atom level. Now, from this perspective, picture light reflecting off of these tiny, tiny, tiny spheres. Reflecting off in all directions. You can change your view to look around the small spheres, and you can 'see' a solid sphere of light reflecting off of them, every direction, up, down, left, right, every point in between. You can picture it a bit like the Everlasting Gobstopper's diagram, where there's a small candy "core" (your molecule), and then the sphere around the core. except that this "sphere" extends infinitely outwards from the molecule. Now take a step back.
You're looking at many molecules now, picturing this "sphere of light" around each one. Lets say you're looking at six molecules, stacked two on two on two, and you're looking at the direct center, in-between the two in the middle row. So, since you're looking at this exact angle, picture only the light that will "get to" you from that angle and you'll notice: You're only 'seeing' parts of the each of the molecules "light spheres." From the top left molecule, you're only seeing the light reflected down, and to your right. From the top-middle molecule you only see the light that it reflects "downward" to you. You're only seeing the right and left sides of the middle left and right molecule, respectively. And with the bottom molecules, you're only seeing the light that is directed "upwards" at an angle. Step back again to the microscope view.
These "bumps" that you see, are really made up of many many molecules, and you understand this now. But from this far, you're only seeing a fraction of the light shining off of each molecule. but there's billions of molecules, all shining light in 3 dimensions. From this perspective, if you keep picturing the light coming off of the molecules, you can see that all of these "light spheres" from all of these molecules, make a criss-cross type of pattern. At any point, you can be seeing the intercepting-points of light reflected from many many molecules. These are what are called "focal points" in optics circles. Now step further back.
From here, you're back to seeing many larger bumps. However, now you know that each bump is made up of other bumps made up of other sphere-bumps of molecules. You're still seeing only the parts of the the light that the bumps-smaller bumps-molecules reflect to that point. This is where you can begin to notice the "inverting" that images go through. The bumps-molecules on the left hand side, are shining light to-the-right, which is where you are: to the right of the molecule. So picture a small point that is "observing" this light. The right side of the point is receiving light that is shining towards the right. Does that make sense to you? If you shoot a basket-ball from the left side of the rim (from the board's point of view) towards the hoop (towards to the right)it would hit the right side of the rim (from the board's point of view) before it went in. Same with light.
So what does this do? Well, since the part of the light that you see from an object to the left of you, is the light that is coming towards your right, it is "received" on the right-side of a receiving device. Same with objects above and below your reference point. The objects above you, are reflecting light "downwards" towards you, and so you receive them on the bottom of your receiving-device. Vice verse for objects below you, they're shining light "up" towards the top of you receiving device. This explains the "inverted image" of pinhole cameras.
So what about perspective? How does this help you picture why things look smaller, the farther away they are? Well, it's a little difficult to explain, but think back to those "focal points" which are where the light from all objects in your viewing range criss-cross into an image you can receive. When you're really close to an object, each "criss-cross-point" is made up of a large portion (percentage) of light reflected from each object. There's more "information" from each point of the object received at your point of view. You can think of this as a higher "resolution," more data at each point. Step back again from the magnifying-glass view, to viewing our ball from about a foot away. Each molecule of the ball is reflecting light outwards from it in every direction. The farther away you are, the less of each molecule's light you see at each point. Now that we're a foot away, each molecule's "light-information" ("density" of the amount of light you're
seeing from each molecule) is far less than when we were up close. So you see less of the light from each molecule, less resolution... Smaller image.
Ok, so now we (hopefully) can picture why perspective is. But what about this "every point is made of the whole image" stuff? What about the eclipse-trees? Well, this is where the "focal points" come into play. Remember how each focal point was made up of some criss-cross section of the light reflected from an object in all 3 dimensions? Well, it turns out that you can picture it like this: Every point of light reflected from the ground, is made of the entire image of the sun. Each point on the ground, is receiving light from a different angle of the entire sun, so one point gets so-and-so much reflected down from the top of the sun, and so-and-so much from the middle of the sun, from each side, from the bottom, etc. What's special about an eclipse? Well, in an eclipse, there's a portion of the sun, that you're not receiving light from. Let's say the moon is eclipsing the bottom left part of the sun, so you see a crescent shape of the sun, a ball with a bite taken out of the bottom left part. Let's picture how this light would shine through a tree.
Picture that you're looking at the ground during an eclipse, and there's a tree above you. For simplicity we'll only look three leaves of a tree, overlapping each other in such a way that you get a hole in the middle of the three. So we're looking at the ground, observing the light that is shining through these leaves. Where does the light that we see on the left-side of the ground come from? Well, this is the light that comes from the sun's right-side. It's projected from the right side of the sun, towards the left, and so we see the right-side of the sun, on the left side of the light shone on the ground. So since the moon's blocking the left side of the sun, the right side is an image of the whole right-side of the sun. Where did the light come from that we are seeing on the right-side of the gound? Well, this is the light that's coming from the left side of the sun, towards the right. But, since the moon's blocking that part of the sun, we don't see any light, it's part of the shadow. I hope you can picture this, we see a representation of the eclipsed sun on the concrete, because the light that would be coming from the left side of the sun, to the right-side of the concrete, is eclipsed by the moon! So we see no light on the right, because none is coming from the left.
hat does this mean? Well, this means that every part of the ground is receiving this "eclipsed image" of the sun! But why do we only see the eclipse through the trees? Well, every point of the concrete is made of an image of the whole sun, but you see a uniform amount of light, because all of these points are overlapping each other. the eclipsed-part of the sun, is overlapped by the non-eclipsed part, making it appear uniform-light. Normally, the eclipsed part of the sun (the part blocked by the moon) wouldn't be casting any light, but since they're all overlapping, you can't notice. They're there, but its' only when the leaves of a tree block the rest of the light that would be coming at that angle, that you can see that parts that are blocked!
This, is the way that I have finally learned how to picture light. I hope that it wasn't too confusing, just close your eyes and go through the exercise again, and it should hopefully begin to make sense. Unless you knew this all along, in which case I am envious. I don't know why I've never been able to fully-understand light, I consider myself a semi-smart individual. Like I said, I've known all of the facts the whole time, but just never been able to picture it. This actually also explains perspective and telescopes. Perspecitve, because if you look at an object at an angle (say, a box from front-on and to the left, you're seeing a high percentage of the light representing the front of the object, and only a portion represenging the length and depth, hence forshortening. Also, telescopes, with a larger lense, you're collecting a higher percentage of focal-points representing the various parts of the object you're looking at, all focused into one area, hence it looks larger, and in a higher detail. Hopefully, there are other semi-smart individuals that were in the same situation, and have benefited from this.