Visual interference with pilots
Safety experts are primarily concerned with visible lasers causing potential “visual interference” with pilot performance. They have identified these three hazards:
- Temporary flashblindness. The pilot is temporarily unable to see (like a camera flash) until the afterimage fades.
- Glare and disruption. The pilot cannot see past the light glare, until the light stops. The glare is bright enough to disrupt normal operations.
- Distraction. The pilot is distracted by the steady or flashing laser light. It is significantly brighter than other nighttime sources such as streetlights, runway lights, car headlights, etc.
But when a pilot is flashblinded on final approach, the situation can be very dangerous. This is especially hazardous because even a low-powered “legal” laser pointer can be a distraction at a distance of two miles. Obviously, more powerful lasers are of even greater concern.
FAA photo illustrating what laser illumination of a cockpit can look like. Because the beam usually cannot be held steady on the cockpit, pilots experience one or more flashes as the beam crosses the windscreen. An animation on this page illustrates the effect.
Note that visual interference happens only when the laser emits visible light. Also, because the eye is more sensitive to green light, a laser emitting green light will cause more visual interference than a laser of equal power emitting a red or blue beam.
Potential eye injury
Laser and aviation experts also consider the potential for eye injury to pilots (or anyone onboard looking out a window when laser light enters):
- Eye hazard. The laser’s light could be powerful enough to cause temporary or permanent damage to pilots’ eyes. Eye damage can be caused by visible, infrared or ultraviolet laser light.
Note that eye injury can occur from any type of laser beam: visible or invisible (infrared, ultraviolet).
A 5 milliwatt laser: a distraction 2 miles away
In the United States, lasers sold for pointing uses cannot exceed 5 mW. The diagram below shows the hazard distances for a 5 milliwatt “U.S. legal” green laser pointer:
- It is a potential eye hazard from the pointer to about 52 feet.
- It is a temporary flashblindness hazard from the pointer, out to about 260 feet. On the diagram, this is illustrated in the inset photo “Near-flashblindness” which shows what a 5 mW laser looks like at 350 feet.
- It is causes glare and is a disruption hazard from about 260 feet to about 1,200 feet. This is shown in the “Glare” inset photo where the runway is not visible.
- It is a distraction hazard from the pointer to over two miles (11,700 feet). The distraction can be dangerous during a critical phase of flight, such as takeoffs and landings.
The laser’s light is not truly safe until it is indistinguishable from background lights on the ground. A pilot may notice a flashing dot of light, but it should not be enough to cause a distraction. (This does not mean that anyone should aim a 5 mW laser at a plane if it is over 2 miles away. For one thing, it is very difficult to gauge aircraft distances at night. Even more important, there simply is no reason to aim a laser at an aircraft except in an emergency situation such as a wilderness rescue.)
Click on the diagram for a larger version
For more info on the inset photos (cockpit views of laser light), see the “Effects on pilots” page
A 125 milliwatt laser: a distraction 11 miles away
More powerful lasers are hazardous at greater distances. The hazard increases as the square root of the power increase.
For example, a 125 mW laser is 25 times more powerful than a 5 mW laser. The square root of 25 (the power increase) is 5 (the hazard distance increase). Therefore, multiply the hazard distances for a 5 mW laser by 5, to find the hazard distances for a 125 mW laser. For example, if a 5 mW laser is an eye hazard out to 52 feet, a 125 mW laser is an eye hazard out to 5*52 or 164 feet.
The table below does the multiplications for you. It provides some sample laser powers and the corresponding hazard distances measured from the laser output. (Note that these distances are approximations. It is not as if a 5 mW laser is an eye hazard at 52 feet but is not an eye hazard at 53 feet. The distances give approximations where one hazard zone shades into another.)
Click on the table for a larger version showing additional data
How to be safe when using lasers at night
If you absolutely must point something out in the night sky (e.g., at a star party), use the laser to circle the object -- don’t aim directly at it. Additional suggestions are on the Tips for outdoor use page.
For the FAA’s viewpoint, see the 2009 FAA/Air Force aircraft laser illumination video, and the 2010 FAA publication “Laser Hazards in Navigable Airspace”, also known as “Medical Facts for Pilots” (AM-400-10/3).
Studies from the FAA and others are in the “Info from FAA etc...” section of this website.
Articles from other aviation sources, and presentations to laser safety groups, are on the Links page.