A powerful pulsed laser intended for overhead use only was pointed into a crowd attending a music festival outside Moscow earlier this month, allegedly causing retina damage in dozens of people. A pulsed laser can be up to 100 times more powerful than those recommended for aiming into an audience and never should have been allowed, according to the head of the International Laser Display Association (ILDA).

ILDA Executive Director Patrick Murphy said the dotted-line beam pattern in a video taken at the Aquamarine techno music festival and posted by Russian news agency NTV on its Web site shows that it was a pulsed laser, such as an Nd:YAG laser, that was used. The correct laser would have had a solid-line pattern, he said.

Pulsed lasers are most frequently used for medical and industrial applications, ILDA said. While the beam may look continuous to the eye, it actually consists of light emitted in short, rapid and powerful bursts. Each 250 billionth of a second burst contains about 100 times more energy than light from an equivalent continuous-wave laser.

"Never take a pulsed laser and aim it at an audience. That's safety 101 within our industry," Murphy said. ILDA has 150 members in 34 countries who conduct laser shows or sell the equipment. The association promotes use of laser displays in art, entertainment and education and also represents the industry on safety issues.

The "open air" music festival, held about 50 miles outside Moscow, was supposed to take place outside, but a tent was erected when it started to rain. When the decision was made to hold the event under the tent, that laser never should have been used, Murphy said.

"That kind of laser can be used for light shows overhead, if the ceiling is high enough, or aimed into the sky -- it's fine for that. Once you aim it into an audience, it's dangerous, and the operator never should have allowed that," Murphy said. "Some later press accounts indicate that the injuries may not be as severe or long-term as was first reported. Nevertheless, it never should have happened in the first place."

Murphy said ILDA has one member in Russia, and "he assures us that he wasn't involved" in the Aquamarine show. "This was some kind of domestic laser, used with extreme incompetence and irresponsibility. Everyone in our industry knows not to use a pulsed laser," he said.

After the festival 60 people sought medical treatment at eye hospitals in Moscow, NTV reported. Several ravers wearing sunglasses interviewed by NTV after the festival said their eyes had been damaged by the laser. Digital cameras, cell phones and video equipment were also reportedly damaged (See Revellers' Retinas Wrecked).  Russian media later said 12 cases of laser-induced blindness had been confirmed.

The newspaper Kommersant quoted one doctor as saying "All of them have burned retinas, you can see scars on them. The loss of eyesight in some cases is up to 80 percent and it's unlikely it can ever be restored." But anonymous sources subsequently cast some doubt that the retinas were burned, saying there were hemorrhages only and speculated that drugs could have been involved (See Laser Blamed, Drugs Eyed).

Since the incident, Murphy said ILDA members have been receiving calls from clients concerned about the lasers used at their events. In response, ILDA has moved safety documents on its Web site from the members-only section to be available to the general public, and is requiring its members to read a laser safety summary it has prepared. Among other requirements, members also have to sign a document saying that they will not use pulsed lasers for audience scanning.

Laser shows have been held for 40 years, and in that time only two other incidents like the one in Russia have been reported, Murphy said, and both were due to the misuse of pulsed lasers.

When done properly, he said, scanning a crowd with lasers is "stunningly beautiful" and can give the impression of "being in the middle of fireworks. It's way better than overhead beams and graphics on a wall." He estimated that every night 1000 laser shows are conducted around the world in different venues.

For more information, visit: www.laserist.org