Are laser pointers really dangerous?
Reports of aviator crews being “blinded” by visible green laser beams has led to speculation in the media of a possible security issue, but many have asked why the flurry of new reports after a period of relative quiet on the misuse of laser pointers.
ABERDEEN PROVING GROUND, MD - Reports of aviator crews being “blinded” by visible green laser beams has led to speculation in the media of a possible security issue, but many have asked why the flurry of new reports after a period of relative quiet on the misuse of laser pointers.
Visible laser beams created a stir about a decade ago in the aviation community following a flurry of incidents of laser beam illumination of airline cockpits at night during final approach at several airports around the United States. At that time, laser lightshows, using multi-Watt argon and krypton lasers, had come into common use to attract customers to casinos in Las Vegas and elsewhere around the country. Xenon-arc searchlights had been used for many decades at the opening of events or at special events to attract notice of people in the surrounding countryside at night. Pilots had grown accustomed to such searchlights, however, and there had been no strong efforts to regulate the use of searchlights in regulated airspace. The laser illumination incidents in the 1990s did not cause any documented instances of permanent retinal injuries, but the FAA updated their guidance (FAA 7400.2D, now 7400.2E) for use of lasers in the airspace to address the important safety issue of distracting aircrew during take-off and landing.
A survey of pilots was conducted by the Southwest Airline Pilots Association in the 1990’s and reported at the International Laser Safety Conference in 1997 (Sliney, 1997). Incidents of illumination by searchlights were compared with lasers and typically most pilots felt that they had never been bothered by any high intensity optical source searchlight at distances of much more than 2 to 3 km; whereas, afterimages distraction and similar visual disturbances were experienced out to 5 or even 9 km from laser beams. The duration of afterimages or distraction after laser illumination was greater than reported due to searchlights.
Aviators who have been frequently illuminated, such as some low-flying urban helicopter pilots, have learned to maintain aircraft control, not to stare into a laser beam and to limit any direct viewing of the laser. Proper training and situational awareness can apparently reduce startle and distraction from visual effects. Aviators who are familiar with occasional searchlight illuminations have come to accept these, where the actual illumination levels are similar to light-show lasers and certainly greater than from laser pointers. In addition, dirty or scratched windscreens tend to increase scatter of light and can produce a more dramatic visual effect in some instances.
Mean green beams
Class 3A laser products are now also termed Class 3R laser products and have an output power emission between 1 and 5 mW. These lasers are in a transitional category between power levels where the aversion response (blinking and turning away) provides protection against injury and power levels were the aversion response is inadequate and where retinal injury becomes more likely (Class 3B).
Amateur astronomers are now using green laser pointer beams with output powers of 5 mW and even higher, to point out objects in the night sky. Most are unaware of the potential risk to aircrews should they directly illuminate a plane. The US Army CHPPM acquired a number of commercial laser pointers and noted that some lasers labeled as Class 3A were indeed 3B with output powers of the order of 10-20 mW.
Temporary visual effects on aircrew vary, but they range from startle or distraction to discomfort and disability glare with dazzle and even after-images or flash blindness. Startle refers to an interruption of a critical task due to the unexpected appearance of a bright light such as a laser beam, whereas glare and dazzle refer to a bright light that makes it difficult to see, such as oncoming headlights or momentary laser pointer exposure. These visual effects last only as long as the light is present. As the sun sets and backgrounds become darker, a small laser at a distance becomes more visible. It is unlikely that real after images would be produced by the recently reported aircraft incidents related to ground-based laser pointers. With laser light show beams, which are a hundred to a thousand times brighter, after images may occur.
In most individuals the aversion response protects against risk of eye damage from accidental viewing of Class 3R commercial laser pointers even at relatively close distances. Brief exposures during the performance of critical tasks, however, can be disruptive and could cause accidents.
David Sliney is a physicist and program manager at the U.S. Army Center for Health Promotion and Preventive Medicine, Aberdeen Proving Ground, MD 21010-5422. E-mail: David.Sliney@apg.amedd.army.mil; URL: http://chppm-www.apgea.army.mil/laser/laser.html. (See web exclusive for full article.)