For example, I’m sitting on my front porch which overlooks the town. Miles away I can see streetlights, signs, etc. How does the source project light to my location, yet doesn’t illuminate my location?
Holy moly friends, thanks for the awards and stuff. I didn’t think this question would spark so much interest, lol. I am thoroughly grateful for all your replies.
In: Physics
Damn guys, so many answers so quickly! Thank you all for your explanations. Makes a bit more sense now. I haven’t really studied much physical science since high school and that was a while ago so pardon my ignorance on the subject. I just had the question occur to me while I was outside this evening, and Google wasn’t much help. You all were though!
I have a question to add. I was watching a debunking of a flat earther that said the moon was only 50 miles away because he could hit it with his laser pointer. The debunker said the light would not reach the moon because it would be too spread out by the time it got there. But then Ingot to wondering about how we see stars. Wouldn’t their light be very spread out over the extreme distances? Why are we able to see them as points of light. At best, shouldn’t they be really fuzzy blurs?
It’s a question of numbers. In a pitch black room, your dark-adapted eye can almost detect single photons, little packets of light. The more photons that hit your eye at any moment, the brighter the source.
To make out an object, your eye needs to receive lots of photons all at the same time. That cross-town street light is blasting photons out into space in all directions and your eye is picking up the few photons that travel directly from the light to your eye. There simply aren’t enough of them that hit some object near you and then bounce into your eye, all at the same time.
A camera doesn’t care about time. You can leave the shutter open and it’ll collect photons all night *and remember them*. After a bit, it can collect enough photons to make out Andromeda, a galaxy that occupies more of the night sky than a full moon. Our eyes don’t remember photons over time so we can’t see Andromeda without using a telescope or camera.
Imagine it is dark and you shine a torch at the wall. The light spreads out like a cone, getting more spread the further it gets from the torch. Some of the light hits the wall . Some gets absorbed by the paint and some gets bounced back. Some of that light hits you eye and that’s how you see. If you shine at a mirror a lot gets bounced back. If the wall is black less gets bounced back.
Ok so that’s reflected light. Each time it hits something only a fraction gets reflected/scattered back.
If your twin shines the same torch from a mile away at you, then the light that hits your eye hasn’t hit anything between the torch and your eye. That is direct light. Your eyes are sensitive and if everything else is dark then your eye will notice the one light even if it is far away.
It’s the same reason that looking at the sun will burn your eyes ( never do this ) . Direct sunlight is really really strong . But if it’s sunlight that’s bouncing off a tree or a person then most if the light is absorbed and scattered so then it’s ok and your eye can even distinguishes which bits of light it sees. Red…blue…etc.
The absorption of light is why thing get hot when left in direct summer sunlight, more so than when they are in the shade and only get reflected light
Our sun is a star that’s very close. Other stars are a long way away but we can still see them even when it’s dark.
[edit]spelling
Light sources “illuminates” an area by sending out light rays (photons). Those rays hit surfaces, get partially absorbed then bounce back carrying the surface’s color with them. For this to work well you need a lot of rays hitting the same area and bouncing back to your eye.
The farther away from the source you are the less dense the rays are (imagine a shotgun blast opening up as it flies out).
Less rays means that there are very few chances enough of them will bounce off the same surface and back into your eye to carry the color. As a result your surrounding aren’t “illuminated”.
However, nothing is preventing the couple stray rays from hitting you straight in the eyeball.
“Illumination” in your definition means that you’ll be able to “see” an object in that light. But objects absorb energy and disperses the light even further. So while your eyes can pick up the light from the source, it might not pick up light reflected off nearby objects.
You can test this effect with a simple thought experiment. Let’s suppose you are in a stadium with only one light source, we then turn the light down such that you cannot see your surroundings but only that source of light. Turn around, and hold up a mirror. That mirror is “illuminated” because it reflects almost all of the energy that hits it. In that sense, if you replace your nearby grass with reflective materials you will see that the light from the stadium does infect illuminate your surroundings.
Also the “inverse square law” answer is a red herring, while it correctly describes why the “divergence” of light increases, the intensity of light does not decrease simply with distance.
Every light source sends out loads of tiny light blobs that fly out in a straight line and illuminate anything they touch. Most of these hit into stuff near the light source cos it’s closer so we can see it lit up. There are so many flying out that some of them are bound to hit your eye, but not enough so they are able to light up the area.
Kinda like a blunderbuss.
Consider the most extreme example of a distance source of light that we see, but that doesn’t illuminate our surroundings: stars in the night.
If you put a mirror on the floor at night, the mirror *will* reflect the starry night. This proves that the “culprit” is the materials around you. The light from stars is so dim and weak that the portion of it that gets reflected by ordinary materials is too negligible for even our eyes to notice it.
Imagine a circle, and a 100 lines protruding from the surface, all equally spaced.
Anytime one of those lines hits an object, the object lights up, proportional to the number of lines hitting it.
On your porch, you can sort of visualize a bunch of lines hitting the porch.
If you’re a mile away, you might be lucky if one of those lines hits your face. That one line, is going directly into your eye, and your eye can pick it up, as it’s specifically designed to pick up light.
Actually, Venus can be bright enough to read by, in an extremely non-polluted environment, in clear weather.
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