Do torches have a beam length? or am I imagining things again..

[AusKipper]

Not sure if anyone has ever noticed this, but when I shine a torch straight up into the sky, it looks a bit like a dull fat one of those lightsabres, it goes out, and then just stops, abruptly.

Does it really do this? why does the light reach a certain distance and then stop instead of gradually fading out? or is it just the angle i am looking at it from?

Logic (to me) would dictate that the light would do something like this (| represents a photon.. the close the photons together, the brighter the beam)

||| | | | | | | | | | | | | | |

But instead it seams to do this:
||||||||||||||| | |

I have no idea if i am making any sence or not, i'm sure you will all let me know..

Looking forward to the replys...

 

[AusKipper]

Ok, the forums is playing tricks on me. Looks like i cant have more than 2 spaces in a row. Basically what it should have been is ||| then another 3 | with 1 space, then another 3 | with 2 spaces, then another 3 | with 3 spaces, etc etc etc

 

[Norm]

Look here Inverse Square Law
Your light doesn't just stop.
Norm

 

[defloyd77]

I've noticed this too, I know it doesn't just stop, but for some reason it does appear as it does.

 

[Zeruel]

I think they do fade off, maybe that can be better seen if it's viewed from a distance rather than you holding it and seeing from the light's angle?

 

[Moonshadow]

Probably a combination of the inverse square law, atmospheric scattering and the logarithmic response of the eye.

 

[StarHalo]

There's also the optical illusion of the light seeming to angle towards you if you have it pointed straight up - there are all kinds of interesting variables that trick the eye.

 

[divine]

The light spreads out (spherically radiated from the front of the light) the further away it gets. I think if you had a very good thrower beam, with all of the light going in the same direction... it would decrease in brightness much less.

The density goes down as the beam spreads out.

Now, if you had an ideal focused beam, I think it would decrease in brightness from particles that get in its way or from the medium it is being transmitted through. Air isn't perfect, a vacuum tube would be better.

 

[matrixshaman]

Nope - all above incorrect. Your beam has simply reached the end of the Matrix in which you live. You've just found the outer limit of it.

 

[Zeruel]

Nope - all above incorrect. Your beam has simply reached the end of the Matrix in which you live. You've just found the outer limit of it.

You're right. So... do you pick the red pill or the blue pill after that?
Maybe the agent can tell us where the beam went...

 

[Mjolnir]

In some cases, it is for the same reason that you cannot see things that are very far away on some days, and on other days you can see them (not considering the curvature of the earth, of course).
The particulate matter in the air reflects some of the light; that is why you can see the beam. Since the distribution of these particles is essentially random, the farther the beam goes, the greater the amount of the beam that gets reflected, since the amount of particles increases, but the amount of light does not. Eventually, these particles will reflect too much light for a beam pattern to continue to appear (because the light isn't intense enough to reach the particulate matter higher in the air, or because it is not intense enough to make it back to your eyes after it is reflected). If you are right under the beam (which is pointed vertically), it will seem like the beam just cuts off, since layer upon layer of particles add together to form a sort of reflective "surface" over a span of a certain distance (of course this depends on how much is in the air). The beam is really gradually dimming, but when viewed from underneath it all seems to be reflect back at the same distance, as if it hit a ceiling. This is because the beam angle does not change, so your eyes have a hard time telling how far away the beam is when it reflects back (if you have no point of reference).
I doubt what I just said makes any sense at all, but that is the best way that I can explain it using only words.

Of course, sometimes the "beam cutoff" produced by my HID spotlight is because of the beam hitting the cloud ceiling.

 

[StarHalo]

Of course, sometimes the "beam cutoff" produced by my HID spotlight is because of the beam hitting the cloud ceiling.

Pretty sure that's an illusion also - the beam atop the Luxor appears to cutoff abruptly too (and it always appears to be angled towards you, regardless of what side of the casino you're on, hence my note above)

 

[Black Rose]

Of course, sometimes the "beam cutoff" produced by my HID spotlight is because of the beam hitting the cloud ceiling.

I'd love to do that but I live on the flight path to an international airport....they frown on those kind of things.

 

[Black Rose]

Where I live there is a fairly large field right in the middle of all the houses.

I'll sometimes go out at night and target a tree I know the light won't light up well or at all.
I then shine the light at a street sign even farther away, and it lights up the sign big time - the light just keeps on going.

 

[Mjolnir]

Pretty sure that's an illusion also - the beam atop the Luxor appears to cutoff abruptly too (and it always appears to be angled towards you, regardless of what side of the casino you're on, hence my note above)

No, hitting the clouds is not an illusion. I have indeed hit the clouds with my Stanley. I looked up the cloud ceiling for an airport nearby, and on the occasions when I could do a cloud bounce, the clouds were only at about 500- 2,000 feet.

 

[herbicide]

I then shine the light at a street sign even farther away, and it lights up the sign big time

That's because street signs are retroreflective - they bounce the light straight back at you, with very little scattering.

 

[Moonshadow]

Exactly - street signs are designed to reflect light, whereas the whole purpose of a tree (if you think about it) is to absorb most of the light that lands on it !!

 

[AusKipper]

The particulate matter in the air reflects some of the light; that is why you can see the beam. Since the distribution of these particles is essentially random, the farther the beam goes, the greater the amount of the beam that gets reflected, since the amount of particles increases, but the amount of light does not. Eventually, these particles will reflect too much light for a beam pattern to continue to appear (because the light isn't intense enough to reach the particulate matter higher in the air, or because it is not intense enough to make it back to your eyes after it is reflected). If you are right under the beam (which is pointed vertically), it will seem like the beam just cuts off, since layer upon layer of particles add together to form a sort of reflective "surface" over a span of a certain distance (of course this depends on how much is in the air). The beam is really gradually dimming, but when viewed from underneath it all seems to be reflect back at the same distance, as if it hit a ceiling. This is because the beam angle does not change, so your eyes have a hard time telling how far away the beam is when it reflects back (if you have no point of reference).
I doubt what I just said makes any sense at all, but that is the best way that I can explain it using only words.

Yeah, I can sort of make sence of that... seems like the most reasonable explination to me

I'm glad others have noticed it too.

I have also noticed that that beam distance (where it cuts off) is quite a bit shorter than how far it can actually shine. ie, lets say it looks like its shining 100m in the air, if you lower it down to a point where it should cut short of a tree top, it actually lights it up. So it must actually be shining up a fair bit further than it appears, and of course with nothing up in the sky to judge the distance.... yeah, its all very confusing to me lol

 

[Norm]

Just remember the inverse squares ratio, the beam is increasing in size the further it travels, the light never actually stops the beam just continues to spread to infinity and beyond If your light was tightly collimated like a laser it would be seen to travel further, not because it is travelling further just that the light is kept from spreading out at the same rate.
Think Mag aspheric and the same light with a reflector.
Norm

 

[Black Rose]

Exactly - street signs are designed to reflect light, whereas the whole purpose of a tree (if you think about it) is to absorb most of the light that lands on it !!

True, but when the sign is 100+ feet past the tree and still lights up, it proves the point that the light doesn't stop at the tree just because you can't see the light on the tree.