A green laser can be picked up at any place for around Rs 800 (less than US$ 20). The beam is powerful, and the laser loses very little intensity in its propagation through air. Infact, the beam is so powerful that it can damage your retina, blinding you for life.
Irresponsible use of the powerful green laser is most observed by aircrew. A low flying aircraft on approach gives a sadistic thrill to those with a laser on the approach path: to shine the beam right at the cockpit. While this gives the man or woman, boy or girl on the ground a good few seconds of fun, the effects on the other side, up in the air, are anything but funny.
Firstly, the beam diverges slightly as it propagates through air. What appears as a pencil beam for the prankster is actually a huge green light for the pilot at a distance of around 5 kilometers (2.7NM) on approach. What has also been reported is the way in which the light diffuses when it strikes the windshield, having the effect of illuminating the flight deck, and distracting the flight crew.
Secondly, the intensity of the beam can either temporarily or permanently blind the pilot, especially on approach at night. If the cockpit floods with the green light and the pilot’s eye receives scattered light, vision will be temporarily affected, with the immediate consequence of losing sight of the runway and approach lights. This may lead to the aircraft going below the flight path, and impacting either terrain or buildings on approach. In case the laser beam directly hits the eyes of the pilot, the intensity can blind him or her for life, with immediate and long term consequences. The immediate consequence is the potential loss of control of the aircraft, threatening the lives of the 150+ passengers he is responsible for. The long term effect, if the airplane manages to be landed by the other crew member, is his inability to ever fly again as a pilot.
While admittedly this act is an of fun, and usually by the ignorant, helping spread the word can remove an unsolicited growing threat to flight safety.