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1000mW blue vs 200mW green

uperkurk

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Which one would be best for out doors night use? I want a VERY bright strong beam that can reach miles and miles out
 

blakegriffin

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Both of the beams would be very very visible at night. The green would be better for distance and would be a bit brighter.
 

Moistenator

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Keep in mind that green lasers also emit infared light so you may want to make sure you get something Infared filtered otherwise it will be more like 130mW green, 70mW infa red.
 

Encap

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I think you are out of luck wanting a "beam that can reach out miles and miles" and be seen by everyone within miles. "Very bright strong", no problem.
Beams appear to stop a relatively short distance from the observer approx. 100 to a few thousand of meters regardless of the output power of the laser.

I will try to steering you towards reality of laser beam visibility rather than imagination about same --here goes.

Beam visability to an observer is complicated real world phenomenon of light, eye sensitivity, and reflection from particle/aerosols in the air the details of which are not intuitively obvious.

The beam will go for miles--whether or not you can see the beam depends upon many things -- among them the position of the observer in relation to the source of the beam , amount of aerosols in the air of the Planetary Boundary Layer, an individuals eye sensitivity to any given wavelength.

In a vacuum, the laser beam itself would be invisible - regardless of power or colour. However, as the beam passes through Earth's atmosphere some of the photons encounter large airborne particles which reflect some of the light back to an observer.

You can see a laser beam for the same reason that the sky is blue!

It is extremely small airborne particles called aerosols having a diameter significantly less than the wavelength of the light that causes the beam to become visible.
The effect of minute particles scattering light is called Rayleigh scattering and it's most noticeable effect is to turn the daytime sky blue. Rayleigh scattering causes photons to be scattered in a roughly spherical manner around these particles. Some of the light is scattered forward (in the direction of the beam), a lesser amount is scattered to the sides and about the same amount that is scattered forward is scattered backwards towards the light source. This backwards scattering is why the beam is more visible to people standing near the person using it, than people standing some distance to the side. The more of these minute particles there are in the atmosphere, the more Rayleigh scattering there is

A laser of any power will appear to the observer(s) to stop in the sky due to The Planetary Boundary Layer.
The Planetary Boundary Layer is the lowest part of the Troposphere that is directly influenced by the presence of the Earth's surface. As in fluid dynamics, the air (a fluid) that is in direct contact with the Earth's surface moves very little (ignoring local winds). The air above can be in significant motion (e.g. the jet stream). When two fluids are in proximity where one is not moving and the other is moving a boundary layer must develop to accommodate the transition from one state to the other.

Therefore, the portion of the atmosphere directly above the surface of the Earth is "capped" by a boundary layer. The thickness of the Planetary Boundary Layer changes from day-to-night and from day-to-day depending on local terrain (water, desert, earth, mountains) and local weather. This thickness varies from a few hundred to a few thousand meters as does how far out a laser beam is seen from an observers view.

Beyond the Planetary Boundary layer a laser beam appears to abruptly stop because there are less and less particles to reflect the light, even though the laser beam goes on for many miles.


Exactly how bright and how far vary at any given moment a beam wil be involves a lot more than you imagine.

There is additionally, the sensitivity of the eyes of the observer to wavelength emitted by the laser part which is again a complicated thing to go into and plays a part as well.

Laser dot is different--you can see a dot many miles away.

For more complete information see:
Rayleigh scattering - Wikipedia, the free encyclopedia ,
RASC Calgary Centre - The Atmosphere, Astronomy and Green Lasers ,
and
http://www.laserpointersafety.com/page52/aviationfacts/whybeamsseemtoend.html


As regards relative brightness of different wavelengths here are 2 calculators each using a different curve--neither is 100% accurate but you can you can enter the wavelength and mw values into them and get a pretty good idea of how bright one is compared to another.

Beam: (445nm 1000mw) vs. (532nm 200mw)
and
Beam: (445nm 1000mw) vs. (532nm 200mw)

I hope that helps you decide which laser to buy as your first laser---really the answer is to just get one and some experience and from that determine where you want to go.

Generally higher power 532 green will make a beam the appears much more solid/substancial but not a whole lot brighter example 200mw will be thin and transparent compared to a 500mw most of the time in non-foggy conditions. In fog the will both be brilliant/very substancial as a torch or car headlights are in fog.

PS Know that it takes generally 4X the output in mw to appear roughly twice as bright to the eye which is another complicatied thing to explain.
 
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