Visibility vs Wattage

[quickasult]

Hi all! I have been looking around for cool laser pointers for a while, and i stumbled upon this site. I was wondering if you could help me find what I'm looking for.

At the moment, i do not have the funds for a nice burning laser, but am trying to find one with a strong beam that can be see from at least 2 miles away when shined into a night sky. Is it possible for a 5mW laser to do this, or do I need a 15 or 35 (or perhaps 20?). I am mainly trying to find one within the ballpark price of $50-$75.

Any help would be greatly appreciated.

 

[troyboy]

If you get a 5mW, they are around 20-40 bucks depending on where you buy it. I'm pretty sure that you will be able to see it from 2 miles away

 

[pseudonomen137]

You can get a dot at that range with a 5mW. For visibility, green lasers are the best way to spend your $, but due to a property of lasers called divergence, even if you had hundreds more in your budget you wouldn't be able to get a laser with a very visible beam at 2 miles. Visible dot, sure. If you upped your budget to the $100-120 range you could probably get in the 20-40mW green range and then you'd have a nicely visible beam up close, but still you won't be seeing a visible beam at range. I would suggest finding the cheapest green laser you can get your hands on though for starters, and then see if you need to upgrade from there and save up if you do. Good luck.

 

[Ragnarok]

am trying to find one with a strong beam that can be see from at least 2 miles away when shined into a night sky.

Are you talking about shining it directly AT an observer that far away, or are you talking about being able to see the BEAM in the sky well away from the observer's position? You'll need a lot more power in the latter case.

The angle of the beam relative to the observer makes a big difference, as does the divergence as has been mentioned. Beams in air are LEAST visible when they pass the observer at a 90 degree angle, and much more visible at smaller angles - like right over your head.

Using a telescope in reverse to expand and recollimate the beam will help beam visibility at a distance, as divergence is a scaling factor (for the same divergence, a beam that is 10X the original diameter spreads out 10X less over the same distance).