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July 24, 2012, 03:33:37 PM
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Offline Pierre Joubert

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Careful with those Lasers!
« on: July 24, 2012, 03:33:37 PM »
Lasers are becoming more popular as pointing devices at our club meetings. Some people have a hard time understanding how the seemingly thin, dim beam of a laser can be a significant problem. I found the following information on the web (Google is your friend!) and trust you will be more careful with that laser!

Why lasers can cause eye damage  :o

A laser’s light is concentrated into a narrow beam. If aimed at a person’s eye from close up, most or all of the light goes through the pupil. The already-concentrated light is further focused by the lens onto a sharp (“diffraction-limited”) dot on the retina.

The power density from a 1 milliwatt laser, focused to a point, is brighter than the equivalent area of the sun’s surface. This can cause a detectable change (injury) to the retina, if the laser stays in one spot for a few seconds. This is why in some countries such as the U.K., laser pointers are limited to 1 milliwatt or less.

Fortunately, people have a “blink reflex” where bright light causes blinking and/or moving out of the light. Because the blink reflex automatically limits the exposure time, lasers with an output less than about 5 milliwatts are generally considered safe for the public to use. In the United States, laser pointers are allowed if they are 5 milliwatts or less. However, deliberate staring at a beam under 5 milliwatts can cause blind spots; this has happened to drunk or stupid people.

As laser power further increases, the chance of eye injury increases. Even blinking may not help. Above roughly 50 to 100 milliwatts for visible continuous-wave lasers, even an accidental direct hit on an eye at close range (where all of the beam enters the pupil) could cause retinal damage. If the person was looking straight at the laser, the burn will be in the center of a person’s vision. In extreme cases of eye damage, central vision could be almost fully lost, and the person becomes blind in that eye.

“Lasers that emit more than 5mW output power can cause irreversible eye injury of increasing severity with increased output power. Although illegal and potentially dangerous, they are increasingly available on the Internet and in stores. The FDA wants to make consumers aware that they should not buy these lasers for themselves or as gifts for others.”

Invisible infrared hazards!!

In addition to visible light, some green laser pointers also emit invisible infrared (IR) light. This is most common in cheap, poorly-constructed lasers where an IR filter is not used due to saving a few cents. This can lead to a literally invisible hazard. For example, one laser tested by a U.S. government agency had a dim visible green light while outputting 20 mW of IR (four times the U.S. legal limit)!!



What makes lasers hazardous?

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.

Visual interference is most hazardous during critical phases of flight -- landings, takeoffs and emergency maneuvers. If pilots are illuminated at cruising altitude, there is usually plenty of time and altitude to recover even from flashblindness.

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 - the hazard distance 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.

Laser and aviation experts also consider the potential for eye injury to pilots (or anyone onboard looking out a window when laser light enters). The laser’s light could be powerful enough to cause temporary or permanent damage to eyes. Eye damage can be caused by visible, infrared or ultraviolet laser light.

In some jurisdictions, there are limits on laser power. For example, in the U.K. it is not allowed to sell laser pointers over 1 mW. In the U.S. it is not permitted to sell lasers for pointing applications over 5 mW.

However, you may be in a country without laser restrictions. Or you may obtain a laser which was not sold or intended for pointing but which nevertheless could be used outdoors. The question then is “how much power is needed?”

For yourself or a small group under most outdoor conditions, 5 mW is sufficient. For a larger group, or where the air is especially clean and dry, slightly higher power such as 10 to 25 mW will be better. The absolute limit for this application should be about 50 mW. There is no objective reason to need more than 50 mW for astronomical pointing applications.

The single best way to improve laser/aircraft safety is user education. Media can help by reminding laser owners that they should NEVER point at or near an aircraft, or other vehicle, or a person’s head.

Incidents can be reduced if users know that (1) a laser pointer beam can definitely reach aircraft, (2) at a distance, the beam spreads so much that it can distract or flashblind a pilot, and (3) aiming at aircraft is illegal and many people have been arrested and jailed.

!! Pointing a laser at a vehicle, plane, boat, another person, animal and otherwise dangerous actions are illegal and punishable in every country. !!


LASER CLASSES

CLASS I (1) LASERS: Class I lasers are low-powered and do not emit hazardous radiation under normal operating conditions because they are completely enclosed.

CLASS II (2) LASERS: Class II lasers are lasers that emit accessible visible laser light with power levels less than 1 mW that normally would not produce a hazard if viewed for only momentary periods with the unaided eye.

CLASS IIIa (3A) LASERS: Class IIIa lasers are systems with power levels of 1 to 5 mW that normally would not produce a hazard if viewed for only momentary periods with the unaided eye.

CLASS IIIb (3B) LASERS: Class IIIb lasers are systems with power levels of 5 mW to 500 mW for continuous wave lasers or less than 10 J/cm² for a 0.25 s pulsed laser. These lasers will produce an eye hazard if viewed directly.

CLASS IV (4) LASERS: Class IV lasers are systems with power levels greater than 500 mW for continuous wave lasers or greater than 10 J/cm² for a 0.25 s pulsed laser. These lasers will produce eye, skin and fire hazards.


ABC News' John Schriffen reports:
 
A JetBlue pilot suffered an eye injury when a green laser was pointed directly into the cockpit as the plane was en route to New York's John F. Kennedy Airport.

The FAA says the incident took place Sunday when the green laser was shone through the windshield of JetBlue Flight 657 from Syracuse, hitting the first officer in the eye. The pilot immediately notified the control tower after the incident.

"JetBlue 657, that was about 5,000 feet, right?" the control tower asked.

"Yes sir, 5,000 feet. Two green flashes, and it caught the first officer in his eye," the pilot said.

An FAA preliminary incident report described the pilot's injury as minor but did not provide details. It was unknown whether the injured pilot was in command of the aircraft at the time, but the flight landed safely at JFK 10 minutes later.

"Use caution. I just had an unauthorized laser illumination event about seven miles ahead of you at 5,000 feet," the control tower said. "JetBlue 657, we are looking into the matter."

In 2011, there were more than 3,500 documented incidents of lasers being pointed at aircrafts, up from less than 300 in 2005. Two planes were reportedly targeted by a green laser beam in San Francisco last week. Those pilots were not injured.

"What happens is that pinpoint spreads out as it gets up higher and farther away, and what may seem like a very faint light to you, in a cockpit, gets almost blinding," San Francisco International Airport spokesman Mike McCarron said.

Authorities say they're ramping up their response efforts and pursuing stricter penalties.

"Interfering with a flight crew is a federal crime. So, the FBI has looked into these laser incidents over the last several years," said Richard Kolko, special agent with the FBI. "We've located some of them. Several of them have been prosecuted."

Laser pointers are also subject to state laws in some cases. A Massachusetts man was sentenced to three years in prison in 2011 for shining a green laser at a Massachusetts State Police helicopter in 2007.

A California man was sentenced to 2 ½ years in federal prison in 2009 for aiming a laser beam at two planes as they were about to land at John Wayne Airport in Orange County.
"Where your focus goes, energy flows"


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July 24, 2012, 11:47:33 PM
Reply #1

Offline Colyn Serfontein

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Re: Careful with those Lasers!
« Reply #1 on: July 24, 2012, 11:47:33 PM »
Scary :o
Capture it when you see it ... it is a mere moment in time and will never come by again.
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