Under certain conditions, laser light or other bright lights (spotlights, searchlights) directed at aircraft can be a hazard. The most likely scenario is when a bright visible laser light causes distraction or temporary flash blindness to a pilot, during a critical phase of flight such as landing or takeoff. It is far less likely, though still possible, that a visible or invisible beam could cause permanent harm to a pilot's eyes. Although laser weapons are under development by armed forces, these are so specialized, expensive and controlled that it is improbable for non-military lasers to cause structural damage to an aircraft.
Pointing a laser at an aircraft can be hazardous to pilots, and has resulted in arrests, trials and jail sentences. It also results in calls to license or ban laser pointers. Some jurisdictions such as New South Wales, Australia have restricted laser pointers as a result of multiple incidents.
Lasers and bright lights
In addition to lasers, other bright directional lights such as searchlights and spotlights can have the same dazzling, distracting, and flashblinding effects.
Lasers in airspace
Lasers are used in industry and research, such as in atmospheric remote sensing, and as guide stars in adaptive optics astronomy. Lasers and searchlights are used in entertainment; for example, in outdoor shows such as the nightly IllumiNations show at Walt Disney World's Epcot. Laser pointers are used by the general public; sometimes they will be accidentally or deliberately aimed at or near aircraft.
Lasers are even used, or proposed for use, with aircraft. Pilots straying into unauthorized airspace over Washington, D.C. can be warned to turn back by shining eye-safe low-power red and green lasers at them. At least one system has been tested that would use lasers on final approach to help line up the pilot on the proper glideslope. NASA has tested a Helicopter Airborne Laser Positioning System. The Federal Aviation Administration (FAA) has tested laser-projected lines on airport runways, to increase visibility of "hold short" markings. Because of these varied uses, it is not practical to ban lasers from airspace.
Primary hazards of lasers and bright lights
The photos at right flash because most incidents are of flashes and not of steady illumination. In accidental illuminations there may be just one or a few flashes. Even in deliberate illuminations, it is difficult to keep a hand-held laser focused on a moving target, so there will be a series of longer flashes. With helicopters at close range, it is possible to have a more or less continuous light. The flashes shown greatly exaggerate the duration of a laser flash and use green rather than less visible red light. With a plane traveling hundreds of miles per hour and a laser beam size of only a meter or so, flash durations would be measured in thousandths of a second.
There are some subjects which aviation safety experts agree pose no real hazard. These include passenger exposure to laser light, pilot distraction during cruising or other non-critical phases of flight, and laser damage to the aircraft. The main concerns of safety experts are focused on laser and bright light effects on pilots, especially when they are in a critical phase of flight: takeoff, approach, landing, and emergency maneuvers.
There are four primary areas of concern. The first three are visual effects that temporarily distract or block pilots' vision. These effects are only of concern when the laser emits visible light.
Distraction and startle: an unexpected laser or bright light could distract the pilot during a nighttime landing or takeoff. A pilot might not know what was happening at first. They may be worried that a brighter light or other threat would be coming. Glare and disruption: as the light brightness increases, it starts to interfere with vision. Veiling glare would make it difficult to see out the windscreen. Night vision starts to deteriorate. Laser light is highly directional, so pilots may act to exclude the source from their direct field of vision. Pointer lasers have an illuminance of about 1 lumen/m2, whereas during the day the pilots have to deal with sunlight which is one hundred thousand times stronger. Temporary flash blindness works exactly like a bright camera flash: there is no injury, but night vision is temporarily disrupted. There may be afterimages, like a bright camera flash leaving temporary spots.