Tips for outdoor use
There are at least two potential consumer uses for lasers outdoors:
- Pointing out stars in the sky: This needs to be done with caution. It is an application that requires relatively strong lasers, so that viewers can see the beam shaft (not just the end dot). Further, the beam is aimed at glowing objects in the sky. Because these glowing, point-like objects could be aircraft, outdoor laser users need to be careful.
- Dispersing birds: TactiCult.com does not recommend that ordinary consumers use lasers to scare away unwanted birds. The right type of laser with a wide, low-powered beam is not available so there are too many potential safety problems for the birds, for the laser user, and for bystanders. Also, there is a chance of accidentally having the beam be on or near an aircraft; this is illegal in many countries and jurisdictions. Finally, some species of birds may be only temporarily repelled by lasers; after a few minutes or within a day, studies indicate they will return.
Both applications are discussed in more detail below.
Star pointing tips
Don’t point; circle instead
Aircraft at a distance can look like stars. This is especially true if they are moving towards you, since there will be little apparent motion.
For this reason, NEVER point directly at a dim or unknown “star”. Instead, move in a circular motion around the object. When doing the circular motion, or when “drawing out” a constellation, keep the beam moving and keep it away from any stars. The “stars” may be aircraft.
Use the laser only long enough to point out the object. Once it is identified, leave the laser off. (After all, this is how people observed the sky for thousands of years, before laser pointers were invented!)
The beam does NOT end!
This unretouched photo shows how a beam outdoors can seem to end after only a few hundred meters. This is a potentially dangerous illusion, as described here. The beam actually continues to travel -- even though the viewer can no longer see the light scattered back to them.
In Feb. 2011, a 14-year-old boy was arrested for illuminating an aircraft on approach to Los Angeles International Airport. He told police that he thought the beam “would not go up to the height of the aircraft.” He was wrong, of course.
Instead of a few hundred feet, a beam can be a hazard to pilots miles away. For example, even a relatively weak U.S.-legal 5 mW laser pointer is a distraction hazard to pilots over two miles away. The more powerful beam in the photo can cause serious glare (the pilot can’t see past the light) two miles away, while the distraction hazard is 22 miles!
Therefore, ALWAYS act as if the beam continues on, forever. Don’t let the beam get close to any aircraft or unknown star along either the visible beam path OR its non-visible continuation.
(Quick explanation of the illusion: There are two effects happening. One is that at some point, the beam exits the dustier part of the atmosphere. This means much less light is reflected back. You can no longer see the beam when it is in cleaner air, higher up. The other effect is that while the beam is slowly spreading out, perspective -- like train tracks appearing to converge far away -- counteracts this, so the beam appears as if it is always parallel. An “infinitely parallel” line is unfamiliar to our visual system. We therefore misjudge the beam’s length; a beam that can be seen miles away may appear to the laser owner as if it is only a few hundred feet long.)
For star pointing, green is best. The human eye sees green much better than the same amount of red or blue, so a 5mW green laser appears to be 5 to 10 times brighter than a 5mW red laser.
Looking at a green beam in the sky should not adversely affect night vision. To keep your night vision, avoid looking directly at the laser dot on a nearby or light-colored surface.
In some jurisdictions, there are limits on laser power. For example, in the U.K. it is not allowed to sell laser pointers over 1 mW. In the U.S. it is not permitted to sell lasers for pointing applications over 5 mW. You may be restricted, therefore, in the laser pointers which are available to you.
However, you may be in a country without laser restrictions. Or you may obtain a laser which was not sold or intended for pointing but which nevertheless could be used outdoors. The question then is “how much power is needed?”
For yourself or a small group under most conditions, 5 mW is sufficient. For a larger group, or where the air is especially clean and dry, slightly higher power such as 10 to 25 mW will be better. The absolute limit for this application should be about 50 mW. There is no objective reason to need more than 50 mW for astronomical pointing applications.
Here is one user’s description of the visibility of his 4.92 mW laser pointer:
- “The first time I used it, I was in a rural area, although not very far from the city, and there was a setting gibbous moon. Limiting magnitude was around 5.0, maybe 5.5. The laser was bright and easy to see.... can you see it from a dark spot in the worst light-polluted sky imaginable? Yes, you can see it. Just for perspective, I used it about 45 minutes after sunset. The sky was still quite bright, with 20 minutes of nautical twilight left, and an hour of astronomical twilight. Limiting magnitude was perhaps 3.5. The beam was visible in these conditions. Dim, but unmistakably visible.”
Tips and resources from the Royal Astronomical Society of Canada
The Royal Astronomical Society of Canada has produced a webpage with information and recommendations on green laser pointer usage. At the bottom of the RASC webpage are additional resources such as a brochure, poster and PowerPoint presentation.
Bird deterrence and dispersal
Some consumers have asked about using lasers for bird dispersal.
A September 2003 U.S. Department of Agriculture publication, “Use of Lasers in Avian Dispersal” says that lasers are “safe and effective species-specific alternatives to pyrotechnics, shotguns, and other traditional avian dispersal tools.” A key phrase is “species-specific”. For example, a 2002 USDA study of crows (listed below) concluded that lasers do not work for more than a few minutes of dispersal, and are therefore not recommended for crows.
LaserPointerSafety.com believes there is a difference between serious, professional use, and consumers ordering possibly over-powered lasers off the Internet and simply waving them into trees and the sky. This is especially true in today’s environment where authorities are very sensitive to lasers being aimed into the air by ordinary citizens.
Our recommendation is that consumers should not use lasers against birds, especially Class 3B and 4 lasers (output power of 5 milliwatts or above). If a person feels they must try this, it should be done very carefully, with continuous monitoring of the sky so that aircraft are not accidentally targeted.
Other laser-related dispersal products and information
Note: We do not necessarily recommend consumer use of these products or techniques, especially since aviation officials are sensitive to unsupervised use of lasers in airspace. The items below are listed for informational purposes.