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02-15-2011, 07:19 AM #1
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GreenLaserFreak
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Green Laser Range

Ok, so first off hello everybody! I'm new to this forum, but certainly not new to lasers.

Just got my 124mw green laser and it's bitchin. One thing I've always wondered though. How do manufacturers calculate the "range" of a laser beam?

Now I understand about beam divergence, so I'm wondering if when someone says their laser has, say, a 100 mile range. Is that a 100 mile VISIBLE range or just the range that the output power should create, visible or not? Of course, weather would be a factor, but for argument's sake let's just say it's clear and about 60 degrees.

I did a rough calculation. I have no clue whether or not it's accurate, or even correct for that matter, but I looked at the typical "range" claimed by various manufacturers of your standard 5mw greenie, which seems to state that the range is approximately 1200 feet.

So, I did the following:

5,280ft / 1200ft = 4.4 (how many 5mw pointers output power needed for one mile?)

Then I divided 124(mw) by 4.4 and I get 28.181818...

So it seems that my 124 mw laser would have a range of 28 miles, which seems a little more plausible than say 60 or 80.

Then again, I'm probably the worst person to ask a math question, and am quite possibly dead wrong and have made myself look like an idiot. But hey...I'm sticking my neck out to learn dammit.

This is where I think there may be a flaw in my formula..

If it takes 4.4 5mw greenies output power to go 1 mile (assuming at least that part of my math is correct), that would be 22mw. Divide 22 from 124 and you get 6.2.

Which would mean that my 124mw greenie would have a range of 6.2 miles, which also seems plausible.

Tell me what you guys think.....

02-15-2011, 06:29 PM #2
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RA_pierce
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Re: Green Laser Range

Technically, the range of a beam of light is infinite. Electromagnetic radiation will travel an infinite distance until it is scattered or absorbed.
The only thing that is going to interrupt it is attenuation by an object or the atmosphere. In extreme cases, gravity. :P

The truth is, you can only roughly estimate the "effective range" where the laser is useful for your specific application.
This is determined by the divergence of the laser beam and the power. All laser beams diverge. The angle of divergence can be reduced with the right optics but never to zero.
Also, the eye's perception of light is a bit counter-intuitive. Twice the power does not mean twice the brightness, since the eye's sensitivity decreases as the intensity increases. So, 125mW of green light is not necessarily 25 times more visible than 5mW.

Now, what do you mean by range?

The maximum distance from which the source of light can be observed?
The maximum distance from which you can see the "spot" termination when viewing from the source? (remember that when you are looking at the "dot," the light has to make one trip to the point of termination and then back to your eyes)
The maximum distance the beam through the atmosphere can be seen?

Basically, there are too many factors to get a solid number. And "range" is really a vague term here.
When laser shops claim a "range" of "XX miles" they are merely using a number pulled from their ass to make sales.

What you SHOULD be paying attention to is the divergence angle as that will have the most influence on the "range."

Hope this helps to explain a little.
__________________
DNA works in mysterious ways.

Last edited by RA_pierce; 02-15-2011 at 06:32 PM.

02-15-2011, 09:32 PM #3
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GreenLaserFreak
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Re: Green Laser Range

Quote:
 Originally Posted by RA_pierce Now, what do you mean by range? The maximum distance from which the source of light can be observed? The maximum distance from which you can see the "spot" termination when viewing from the source? (remember that when you are looking at the "dot," the light has to make one trip to the point of termination and then back to your eyes)
Yea, the maximum distance from which the source of light can be observed. I figure spot termination can depend on more than a few factors; your eyesight, conditions, etc.

Quote:
 Originally Posted by RA_pierce When laser shops claim a "range" of "XX miles" they are merely using a number pulled from their ass to make sales.
LOL, yeah I kinda thought that they might do that.

02-16-2011, 12:21 AM #4
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LtKernelPanic
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Re: Green Laser Range

There's a thread over in the multimedia section with two videos of a 200mw green and a 1W 445 blue that are visible 9km (29,528 feet) from the camera. That's right in the range commercial jets fly at when at cruising altitude.

Last edited by LtKernelPanic; 02-16-2011 at 12:24 AM.

02-16-2011, 10:12 AM #5
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GreenLaserFreak
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Re: Green Laser Range

So that's about 5.6 miles. But that still doesn't answer just how far away we can see that light from the source. The video would just confirm that its visible from that distance.

Traveling in the same direction as the beam, further away from the source seems impractical and quite possibly time consuming. There's got to be some mathematical average that can be calculated, just have to figure out the proper equation. Again, I'm horrible at math and couldn't tell ya.

02-16-2011, 04:34 PM #6
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Grix
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Re: Green Laser Range

Serious manufacturers never state a "range" for their lasers. The only companies that does that is cheap chinese ones, like dealextreme, and they take the numbers out their ass. (Apparently the "range" of their 5mW is equal to their 200mW)

02-17-2011, 04:01 AM #7
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GreenLaserFreak
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Re: Green Laser Range

Quote:
 Originally Posted by Grix Serious manufacturers never state a "range" for their lasers. The only companies that does that is cheap chinese ones, like dealextreme, and they take the numbers out their ass. (Apparently the "range" of their 5mW is equal to their 200mW)
Yes, agreed, but I'm serious here......

02-17-2011, 10:46 AM #8
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Grimm
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Re: Green Laser Range

i think it could be worth it to do some field tests on this. set up the laser at something mundane near the outskirts of town on a tripod, then have your buddy drive the XX miles to the target and call him when you fire it out there. would be fun to measure your beam and log the distance (maybe gps both locations) that way you could calculate actual beam divergence AT DISTANCE

02-17-2011, 11:36 AM #9
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elite ares
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Re: Green Laser Range

Quote:
 Originally Posted by Grimm i think it could be worth it to do some field tests on this. set up the laser at something mundane near the outskirts of town on a tripod, then have your buddy drive the XX miles to the target and call him when you fire it out there. would be fun to measure your beam and log the distance (maybe gps both locations) that way you could calculate actual beam divergence AT DISTANCE
I've been thinking about doing just that. There is a radio tower .56 miles from my house that I can see green and red dots but no blue or violet dots. I was going to ask a friend to park right across the street from the tower with a camera while I point different colors at it. First, I want to know if he can see the dot, second, how large is the dot, and third, what would a photo look like from up close.

02-17-2011, 01:13 PM #10
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Grimm
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Re: Green Laser Range

Quote:
 Originally Posted by elite ares I've been thinking about doing just that. There is a radio tower .56 miles from my house that I can see green and red dots but no blue or violet dots. I was going to ask a friend to park right across the street from the tower with a camera while I point different colors at it. First, I want to know if he can see the dot, second, how large is the dot, and third, what would a photo look like from up close.
thats pretty much what i was thinking. If i did it, I would aim at a large wall of a warehouse from across a local farm. that way it could be low enough to get a measurement but big enough surface to hit easily

02-17-2011, 01:23 PM #11
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elite ares
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Re: Green Laser Range

^^^ Unfortunately for me, the tower is my best target. That warehouse wall would be a great target! You could even measure the dot size and calculate divergence.

02-18-2011, 07:05 AM #12
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GreenLaserFreak
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Re: Green Laser Range

Quote:
 Originally Posted by Grimm i think it could be worth it to do some field tests on this. set up the laser at something mundane near the outskirts of town on a tripod, then have your buddy drive the XX miles to the target and call him when you fire it out there. would be fun to measure your beam and log the distance (maybe gps both locations) that way you could calculate actual beam divergence AT DISTANCE
I read the posts after this and the only problem that I have with this is I live in a heavily populated area. There are a ton of lights around which would mess with a reading, whereas being out in the middle of nowhere, that would be a great area to test it.

Maybe I can find a friend to drive with me out to the desert and do a few tests. Just pick a mountain, post up x amount of miles away with my buddy near the mountain and light it up. I think starting out from far away and working my way in might be more effective.....wait a second....

I seem to remember the Luxor (Las Vegas) many years ago, shining a bright green laser from the top of the hotel towards a mountain near Summerlin...was weird to see a slightly dull but large green dot on the mountain and I remember asking what it was. Would be interesting to find out how many mw that one was.

Last edited by GreenLaserFreak; 02-18-2011 at 07:11 AM.

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