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Safe Green Laser Pointer Usage

General NewsBy Leonard Lynch

In the past, there has been a lot of discussion in the news regarding green laser pointers. They are a great tool for amateur astronomers, however, there is great concern by the government that a terrorist might attempt to cause an aircraft to crash by spotting one with a laser. This seemed ridiculous to me for a number of reasons, but because laser pointers are so commonly used by the amateur astronomy community, I wanted to understand the facts better before I purchased one. The following is what I found:

The laser pointers commonly used by amateur astronomers are green, continuous wave lasers emitting light centered at 532nm wavelength. They are required by the FDA to have a warning or danger sticker on them that indicates the class of the device, which in turn depends on the maximum output of the device. The FDA regulates the devices because of their potential to cause eye injury. Most amateur laser pointers are either Class II (output <= 1mW) or Class IIIA (output <= 5mW) devices. Even though the industry is required to label their products as described, random tests have shown that some devices exceed their labeled output. Accordingly, studies described below apply to correct output levels.

The FDA has studied and published reports on laser exposure to the human eye and associated injury. These studies show that tissue damage may occur when the eye is exposed to a Class IIIA 5mW green laser at a distance of 10 feet or less. This fact alone should cause astronomers to understand how carefully these lasers should be handled. Even though eye tissue damage is a serious matter, it is not the critical issue with the FAA. Instead, they are concerned with glare, flash-blindness and after-images when an aircrew is exposed to laser light. The FAA has studied how much exposure affects aircrew and the degree to which exposure can be tolerated in relation to where the aircraft is in its takeoff or approach pattern.

Generally, the airspace around an airport can be divided into 4 regions. The closest region is within 5 nautical miles (5.75 statute miles) of the runway and extends to 1000 feet altitude. A 5mW laser exposure within 2 statute miles of an aircraft in this region is declared harmful. Obviously this is the most critical portion of flight for the aircrew so a minimal amount of exposure can be detrimental. The next region is within 10 nautical miles (11.5 statute miles) of the runway and extends to 10,000 feet altitude. A 5mW laser exposure within approximately 4 statute miles of an aircraft in this region is thought to be harmful. The regions further out from the runway are still being studied.

Our observatory site is not located within an airport region, however, a laser should never be pointed in the area of a passing aircraft! (The nearest operating airport is Fort Smith Regional Airport, at a distance of 13.4 statute miles. -Ed.)

There has not been a documented aviation accident that was caused by the aircrew being blinded by a laser pointer. There have been accidents caused by other bright lights, but not by accidental illumination by a laser pointer. Governments have recognized safety issues and reacted. The FDA issued a warning in 1997 against children using laser pointers at school and the UK outlawed the sale of laser pointers with output greater than 1mW.

The following should be general rules to follow when using a Green Laser Pointer:
  1. Green laser pointers should only be used by responsible adults who know the potential dangers associated with eye exposure to green laser light. Keep Out of the hands of children or adults who may be unfamiliar with a green laser pointer.
  2. Respect the potential harm that a green laser pointer can do to fellow astronomers, and therefore be extremely careful not to shine the laser in anyone's face, or into any reflective optics. This is no child's toy.
  3. When using the laser to point out anything in the sky, be aware of any air traffic. "Spotting" an aircraft is an absolutely stupid idea and potentially dangerous as well. Doing so from our observatory site could also cause liability problems for our organization.
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Safe Green Laser Pointer Usage
Authored by: Matthew onMonday, July 19 2010 @ 10:56 pm EDT
That's right, so we must be careful. The human eye is especially good at transmitting and focusing green light wavelengths onto the retina. If the power of the laser beam is sufficiently high then the natural aversion responses to bright light, such as blinking, looking away etc, will not provide adequate protection to prevent eye injury. Depending on eyesight and how the eye is focused, a power of 50 mW green laser pointers shone into the eye can usually be expected to cause permanent injury to the retina.

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