Figure 1 - 500ft low beam headlight off-axis laser
Figure 2 - 500ft high beam headlight off-axis laser
Figure 3 - 500ft low beam headlight on-axis laser
Figure 4 - 1000ft low beam headlight off-axis laser
Figure 5 - 1000ft high beam headlight off-axis laser
Figure 6 - 1000ft low beam headlight on-axis laser
Figure 7 - Beam diameter on 8 1/2" x 11" paper pad at 1000ft - true color exposure
Figure 8 - Beam diameter on 8 1/2" x 11" paper pad at 1000ft - false color exposure
Figure 9 - 500ft low beam headlight on-axis laser with passing car high beams
Figure 10 - Refractor setup - beam exiting eyepiece
Figure 11 - Beam diameter at 22x
Figure 12 - Beam diameter at 525x
While many amateur astronomers are familiar with the effects of green laser pointers from the pointer-end, few have actually experienced the light glare produced at the beam's terminus from distances between 2,000ft (610 meters) to 1000ft (305 meters). Figures 1 through 9 above partially convey that experience. A better understanding of the glare effects at distance can lead to better practices when using these practical education devices. The visual effects of green presentation pointers cause only a nuisance hazard to bystanders at distances greater than 1300ft (396 meters). At distances under 200ft (61 meters), the combination effect of consumer laser pointer light and photosensitivity and/or phototoxicity in commonly taken medications has not been researched by industry or the medical community. New research indicates that Class IIIA green laser pointers can cause pathological changes in retinal tissue in extreme exposure situations unlikely to be encountered at star parties. The FAA blink reflex zone of 51 feet (15.5 meters) appears low. The FAA glare effect zone extending to 1171 feet (357 meters) was similar to the glare that I experienced. Attenuation is significant beyond 1100 feet (335 meters). At 1300ft (396 meters), the residual glare of a green presentation pointer is similar to a car headlight at that same distance on high beam. Although not a safety hazard beyond 1300ft (396 meters), bystanders at those distances can be inadvertently struck with a faint green light, creating a light-trespass nuisance. A light-trespass can generate conflicts between homeowners and amateur astronomers.
Individual consumers should be aware of the boundaries of FAA outdoor laser display exclusion zones surrounding local airports and avoid use that impacts those zones.
To reduce user conflicts and to improve the image of the amateur astronomical consumer community, one possible community response to recent public controversy regarding these consumer devices would be for leading amateur astronomical groups to develop a joint statement on safe laser pointer practices. This could be done in conjunction with regulatory agencies and industry.
With respect to regulatory improvements, the Federal Aviation Administration (FAA) could better aid astronomical consumer pointer users by recalibrating and republishing its Federal Aviation Administration (FAA) nominal visual hazard zones for Class IIIA pointers specifically for brighter green laser pointers and by subdividing the existing "glare effect" hazard zone2 into two zones - a closer zone where 30% of central vision is impacted (approx. 1300 ft (396 meters) and a farther-fainter glare zone. Few citizens will be aware of the extensive dimensions of FAA "sensitive," "critical," and "laser free" zones around local airports. Some relevant zones extend over 10 miles from an airport. The FAA should develop and publish an internet map database that shows overlays of these zones with area street maps in order to aid citizens with complying with obligations under obscure FAA Order 7400.2E. Adoption of a new flight order, better tuning FAA Order 7400.2E to the airspace needs of aircraft and to amateur astronomer users of Class IIIA lasers, may be appropriate.
The Federal Drug Administration (FDA) might improve its regulation of Class IIIA pointers by including an express dispersion criteria of 1 milliradian, assuming that dispersion is not already covered by ANSI Standard Z-136.1 (2000). Present FDA regulations3 are based on emittance alone and assume dispersion of 1 milliradian. Dispersion between pointer manufacturers varies. As a result, amateur astronomy consumers cannot reliably use green presentation pointers with the assurance that FAA nominal visual hazard zones are at the same distance between pointers made by different manufacturers. The FDA might also use its regulatory power to improve labeling for Class IIIA green laser product inserts. An improved FDA product insert would reproduce the FAA nominal hazard zones in chart form and advise users of the existence of FAA exclusion zones prohibiting the use of lasers around airports. This would give consumers ready access to information that they need to responsibly use these consumer devices.
Both from anecdotal amateur reports and one study, there appears to be significant variation in the actual emittance of green laser pointers that are delivered to end-users but that claim to be under the 5mW FDA limit. U.S. distributors can aid in delivering a more uniform product to consumers by adopting voluntary industry standards on dispersion of Class IIIA lasers, even in the absence of governmental regulation, and by implementing a more aggressive program of testing and rejection of delivery of manufacturers' products that exceed 5mW ClassIIIA limit.
By applying safe practices, amateur astronomers can assure themselves and the public that the educational benefits of these consumer products outweigh their potential social costs.
Most amateur astronomers have experience using green laser pointers used for astronomy education. Use of these pointers is on the rise, in part, due to their new application as a telescope finder.4 From using these pointers for astronomy demonstrations, I became concerned about their potential to cause nuisance light trespass and flash-blindness in bystanders. At 5280ft (1609 meters), these pointers reportedly create a terminal disk (when viewed looking back at the laser from that distance) equal in brightness to a 100-Watt light bulb5 viewed at 100ft (30 meters).
In early 2005, the arrest of a New Jersey man6 and subsequent prosecution7 raised questions about the social costs of allowing the general public access to these consumer devices. The Airline Pilots' Association called for additional licensing restrictions on the public's access to green presentation pointers. "At this point, we think it would be appropriate for the FDA to look into whether more stringent licensing requirements are needed, given the potential abuse by individuals and possibly even by terrorists," said John Mazor, Air Line Pilots Association spokesman.8
The New Jersey arrest occurred after the December 30, 2004 announcement by the FBI that they were investigating a rash of seven incidents since Christmas 2004 of laser beams being directed into the cockpits of airplanes.9 The Deputy Chairman of the Security Committee of the Airline Pilots Association described the incidents as "organized," implying that they were terrorist in nature. But the FBI reported that they had no intelligence of such an effort. The Christmas incidents occurred in Colorado, New Jersey, Ohio and Oregon, preceded by a September 2004 incident in Utah.
Media reports did not indicate whether the New Jersey man was using his laser within an FAA laser-use exclusion zones surrounding many airports.
The FAA regulates outdoor laser emissions surrounding airports and landing corridors.10 The agency establishes "laser free," "critical" and "sensitive" flight zones around airports based on the power of laser emissions. The close airport critical zone level is .005 milliWatts/Cm^2 (5 micro or uW/Cm^2). The farther sensitive operation zone allows a higher level of emissions at .1 milliWatts/Cm^2 (100 microW/Cm^2). In June 2004 study, an FAA study concluded that Class IIIA lasers operating at 5 milliWatts did not effect the safety of flight operations of airports beyond 10,738 feet (2.03 miles, 3.27 kilometers).11
Figures 13 and 14 illustrate dimensions of various FAA regulated emission zones in nautical miles, but the actual size of the zones vary by individual airport. The laser free zone is 5 nautical miles (approx. 5 3/4 statute miles or 9 1/4 kilometers) in diameter surrounding the airport and extends from 0 feet (0 meters) to 2000 ft (610 meters) above the ground. The critical flight zone is 10 nautical miles in diameter surrounding the airport (approx. 11 1/2 statute miles or 18 1/2 kilometers) in diameter surrounding the airport and extends from 0 feet (0 meters) to 8,000 ft (2438 meters) above the ground. Between 5 and 10 nautical miles, the critical flight zone begins at ground level. It is possible to stand 10 miles (16.1 kilometers) from an airport, point a green laser pointer vertically into the sky, and inadvertently emit an impermissible level of green laser pointer light into an FAA regulated airspace - even though no aircraft may actually be visible at the time. As illustrated, using any red or green laser pointer within 5 nautical miles (approx. 5 3/4 statute miles or 9 1/4 kilometers) of an airport boundary is prohibited. The following table illustrates these constraints as compared to the emissions of a green laser pointer:
Where use of laser pointer emissions exceed these constraints, FAA Advisory Circular 70-1 provides guidance on submitting an application to the FAA in order to allow laser use within a restricted zone.12 The FAA maintains a system to collect reports from pilots of incidents of aircraft illumination by lasers.13
The application of FAA Order 7400.2E10 to individual amateur astronomers or astronomy clubs who use green laser pointers is unclear.
FAA Order 7400.2E and FAA Advisory Circular 70-112 are broadly drafted and appear to include individual or astronomy club use. Circular 70-1 states that it applies to "any person/proponent who plans to conduct laser operations in navigable air space . . . Navigable airpspace is airspace above the minimum altitudes of flight prescribed by regulations including airspace needed for the takeoff and landing of aircraft . . ." FAA minimum flight altitudes are 1,000 ft (305 meters) over congested areas and 500 ft (152 meters) over non-congested areas.14 But a 1998 Memorandum of Understanding states that the FAA intends to only regulate "laser light shows and displays, as wells as scientific research or operations, which may project laser light into navigable airspace" and that involve the use of "outdoor, unenclosed Class IIIB or IV laser light shows, . . . or other laser display configurations which could project lasers into navigable airspace." 15 An FAA phamplet entitled "Laser Safety: Whose Responsible?" states with respect to Class IIIA lasers that the FAA "must be notified before any open air laser light shows operate. FAA will not object if the output power of the laser beam is less than or equal to one half watt, that is, the laser is Class I, II or III, so long as aircraft fly no closer than the required 1,000 feet over congested areas . . . there should be little risk from a laser beam of this power. If the show is adjacent to an airport, however, the FAA may object because of the possible risk to aircraft landing and taking off." 16
Violating an FAA order is subject to a $1,000 civil fine.17
The best course of action for individuals and local astronomy clubs is to consult a local attorney for advice.
Whether or not these regulations apply to individual amateur astronomers is less important than minimizing user conflicts and using a green presentation pointer in a socially responsible manner.
Most citizens, from a basic sense of right and wrong, intutitively understand that operating a red or green laser pointer in a landing or take-off flight corridor or within one or two miles of an airport is inappropriate and presents a hazard to flight operations. Few members of the general public, much less the amateur astronomical community, will be aware of the extensive dimensions of these FAA zones, particularly in urban areas. For example, this author resides about 20 to 30 minutes driving time to the local airport, but not on a take-off or landing flight path. I am hard-pressed to recall any instance of a commercial airliner flying directly overhead, except perhaps at cruising altitudes above 30,000ft (9,144 meters). On a common sense basis, infrequent use of a green laser pointer at a local park (something that I have not done) would not appear to present an air safety hazard. Nonetheless, on a straight line measurement, I appear to just reside within an FAA "laser free" zone. That the zone existed could only be discovered after several hours of research and study.
Under unusual circumstances of inappropriate use, Class IIIA green lasers have sufficient power to inadvertently intrude into the landing corridors and airport operation areas with emissions exceeding FAA standards for the FAA critical flight zone. Although each manufacturer's green laser pointer will vary, a rough estimate of that distance is between 800ft (244 meters) and 1000ft (305 meters). As a practical matter, Class IIIA green laser pointers do not appear to have sufficient power to exceed FAA regulated emission limits within the more distance sensitive flight operations zone. Nonetheless, pilot concerns illustrated by the New Jersey case show the need for amateur astronomers to be aware of flight operations and landing corridors in their area and to avoid inadvertent light trespass into those zones which, although lower than FAA regulatory limits, may interfere with flight crew operations.
Social concerns regarding inappropritate laser pointer use are not new and previously had been addressed by criminal laws. In addition to the FAA rules described above, by 1999, many U.S. states and municipalities had laws prohibiting aiming laser pointers at people, police officers, occupied cars and airplanes.18 Penalties range from $50 to $1,000 U.S. dollars and between 30 days and one-year of imprisonment. The state of residence of this article's author is typical. Directing a laser pointer at any law enforcement officer or "any moving vehicle" is a Class C misdemeanor punishable by up to 90 days imprisonment and a $750 fine.19
The New Jersey case represents potential extension of criminal penalties flowing from green laser pointer use to a charge of terrorism under the USA Patriot Act.7 Section 1993 of the USA Patriot Act, in a chapter entitled "Railroads," provides for imprisonment for any person who "willfully . . . interferes with, disables, or incapacitates any . . . captain, or person while they are employed in dispatching, operating, or maintaining a mass transportation vehicle."20 The USA Patriot Act provision parallels FAA statutes that impose a $25,000 civil fine on any person who "takes any action that poses an imminent threat to the safety of the aircraft or other individuals on the aircraft. . ."21 and that impose a criminal penalty of five years of imprisonment for interfering with air navigation by displaying misleading lights.22
Great Britain uses a different regulatory scheme. That country allows the unrestricted sale of presentation pointers to the general public at lower power (Class I and Class II) than those the United States allows (Class IIIA).2
The governmental and industry response almost has uniformly emphasized the need for public awareness of the hazards of inappropriate laser pointer use,23,5,24 but the issue became muddled by a February 2005 announcement by the North American Aerospace Defense Command (NORAD) to begin operational testing of banks of green laser pointers as a warning system to ward off small private airplanes from restricted airspace. A NORAD press release stated that consumer green lasers were "eye-safe and non-hazardous at all ranges."25 Additionally, in 2004, the FAA announced plans to begin testing the use of yellow lasers on airport runways to mark a horizontal "hold" position line on runways during bad weather.26 If the tests are successful, the technology will be used to reduce the 324 runway incursions reported in 2003. Runway incursions involve an airline driving past its "hold" position on to runways being used by other airliners for landing and take-offs.
Discussions between amateur astronomers who use presentation pointers divided into two camps. Some amateurs viewed laser pointers as useful consumer devices with little or no potential to cause injuries to others. Whatever adverse effects presentation pointers may have are socially acceptable and much less than the adverse effects of other common consumer products, for example, like automobiles and guns. This first camp viewed the controversy as being the result of media hype and hysteria. Another camp felt that even if used properly, vision injury could happen to nearby persons from inadvertent strikes by the laser's beam. The American public has a significant minority that is malicious or irresponsible and could easily use such presentation pointers to harass commercial aircraft. There was also considerable confusion over the difference between the transitory laser pointer effects of "glare" verses the one-second effect of "flash-blindness." Additional confusion occurred over the distances that at which these effects occurred as described in the Federal Aviation Administration (FAA) nominal visual hazard zones for Class IIIA laser pointers. The FAA hazard zones are the basis of nominal hazard zones adopted in the related private industry standard - American National Standards Institute Standard Z-136.1 (2000) regarding the safe use of lasers.27
Another underlying question seen in amateur astronomer discussions involved the social appropriateness applying this technology for amateur telescope pointing and public education in identifying the constellations, consistent with the precautionary principle. There are existing non-laser alternatives such as Telrad and 50mm refractor finders for telescope pointing and 2 million candle-watt flashlights for pointing out the location of stars in group settings. Green laser pointers used as telescope pointing devices do have a unique incremental advantage when attached to Dobsonian mounted telescope. Low-cost Dobsonian reflectors have been become very popular in the last five years and currently are the entry level telescope of choice. To use a Telrad with a Dobsonian mounted telescope the user has to knee on the ground to sight up the finder. A green presentation pointer allows the user to remain standing while pointing the telescope.
While the social costs of using laser pointers for astronomy education appear to be significantly the same as for 2 million candle-watt flashlights, the use of green laser pointers for telescope pointing appears to have higher social costs than existing alternatives of Telrad and 50mm refractor finders. The incremental costs of using green lasers as a telescope pointing device include increased user conflicts with other amateur astronomers by increasing light pollution incidents at dark sites, the potential for accidental nuisance light trespass on nearby homes and highways, and the accidental beam strikes on star party participants.
The position of the camp of amateur astronomers who felt that social costs of laser abuse by irresponsible U.S. citizens was too high was bolstered by testimony of the FAA at March 2005 hearings of Subcommittee on Aviation of the U.S. House Transportation Committee on whether consumer lasers pose safety or a security hazard to mass transportation.28,29 Nicholas Sabatini, a FAA Associate Administrator, reported that the FAA has received over 400 pilot reports of laser incidents since 1990. 112 incidents occurred between November 2004 and the March 2005 hearings. Sabatini noted that none of the reported incidents occurred during the critical phase of landing when aircraft are within 100 feet of the ground. Sabatini stated that "[w]hile a few of these incidents have resulted in reported eye injury, no civilian pilot has had any permanent visual impairments as a result of laser exposure." Sabatini also reported that in June 2004, the FAA published a study in which laser pointers were used to disrupt landing maneuvers by 34 pilots in flight simulators.11 Seventy-five percent reported adverse effects resulting in some operational difficulty during flight within 100 feet above ground level, but "all subjects were able to maintain operational control, and safely land the plane or execute a missed approach." The FAA also produced a video simulation of the effect.30 No legislative proposals were found for the 2005-2006 U.S. Congressional session as a result of these hearings.
In May 2005, new questions were raised regarding the medical safety of green laser pointers. Previously, Robertson et al. (2000) reported that long-duration direct exposure with a consumer red laser pointer on the fovea and retina of the human eye (in volunteer patients with eye cancer schedule to have their eye enculeated) resulted in no pathological changes.31. In 2005, Robertson et al. repeated their experiment with a consumer green laser pointer and exposed a volunteer cancer patient's eyes to 60 seconds, 5 minutes and 15 minutes of green laser pointer light.32 Unlike his 2000 study with red laser pointers, Robertson found that green laser pointers produced pathological changes in the in retinal pigment epithelium in the area exposed for only 60 seconds. The principal change was a yellowish discoloration and the formation of granules in the tissue. Conversely, the test involves focusing the beam directly on the retina at an effective distance of zero feet - a condition unlikely to occur in amateur astronomy use. These signs are consistent with eye injuries from industrial laser accidents.33 Robertson (2005) also reported that "[o]ur patient was unable to recognize any defect in central vision . . ." However, any layperson inspecting of the photographs in Robertson's article of the volunteer's disfigured retina will be quickly dissuaded form any notion that there is some safe-harbor from injury during extreme Class IIIA green laser exposure.
No medical studies were found involving the effects of green or red laser pointers and phototoxicity and/or photosensitivity. Some medications taken for common aliments have photosensitive side effects - fewer have phototoxic effects.34,35 After taking medications that causes phototoxicity, a person experiences no adverse effects if they remain out of bright light. However, when exposed to bright light, the chemical either directly or by a changing cell's chemical response causes retinal or foveal cell damage. Zyrtec, an antihistamine prescribed for allegies, is a common medication that lists phototoxicity as a side effect.36
Photosensitivity is a lesser form of the adverse effect of phototoxicity. Implicit in the photosensitive effect is that the drug has altered the eye's chemical response to intense light. Some common drugs that have photosensitivity as a side effect are listed in Table 2.
Robertson (2005) did not report if his patient was taking any medications that would have caused a phototoxic or photosensitive response.
The green presentation pointer used in this report was a Class IIIA37 laser. A new and disturbing trend is the marketing by non-United States suppliers of Class IIIB lasers38 for import to U.S. recreational amateur astronomers.39 Class IIIB lasers can have up to 100 times the emittence power of Class IIIA lasers and can cause serious eye injury. One off-shore hyper-marketer offers these Class IIIB lasers for import to the United States with a disclaimer that the United States' purchaser is responsible to comply with all U.S. FDA regulations.40 An FDA release states the United States Customs Service will confiscate any Class IIIB lasers imported into the United States - resulting in the customer's loss of the purchase price.23 Shipping Class IIIB lasers to persons who do not have an FDA license violates FDA regulations.23
Again, only Class IIIA3,37 green presentation pointers are discussed here.
In order to understand this controversy better, I wanted to learn more about the effects that an accidental strike might have on other star party participants. Like most amateur astronomers, I have used an astronomy green laser pointer for more than a year and I was familiar and skilled with the "business" end of the device. Like many other amateur astronomers, I had no direct experience with the "receiving" end of the presentation pointer. To be able to use these pointers more responsibly, I wanted to understand how far should star parties be from roads or houses inorder to prevent nuisance light trespass. I also wanted to better understand the costs and benefits of these consumer devices and of proposals to regulate them.
In order to learn first-hand about the effects of green laser pointers, I took photographs from a distance of at 500ft (152 meters) and 1000ft (304 meters) of an astronomy Class IIIA37 green presentation pointer placed approximately two feet to one side of a car headlight. Those photographs aided me in understanding ambiguous Federal Aviation Administration (FAA) nominal visual hazard zones for Class IIIA pointers. I could judge the pointer's and car headlight's relative or apparent magnitude and glare.
I concluded that the FAA nominal hazard zone for an averted vision reflex, 51ft (15 meters) appears too small; a more reasonable working distance is 200ft (61 meters). Car headlights on high beam at 500ft (152 meters) and 1000ft (304 meters) are a greater glare hazard than a Class IIIA green presentation pointer, except where the viewer's exit pupil looks directly down the optical axis of the pointer's beam. At 1300ft (396 meters), Class IIIA presentation pointers have an equal glare effect as car headlights on high beam, even where the viewer's exit pupil looks directly down the optical axis of the pointer's beam.
Although not a safety hazard beyond 1300ft (396 meters), bystanders at those distances can be inadvertently struck with a faint green light, creating a light-trespass nuisance and glare. Presentation pointer users need exercise reasonable caution when using these devices in order to prevent nuisance complaints from bystanders, drivers and homeowners within 1500ft (457 meters).
Based on current knowledge, consumer green laser pointers probably do not present a risk of permanent vision injury to participants at a star party within a 200ft radius whose eye pupils are inadvertently struck by the laser's beam.
This also includes inadvertent strikes by laser pointers going down telescope tubes and up eyepieces into observer's eyes. In the case of inadvertent strikes down telescope tubes, basic principles of telescopic magnification should be recalled. First, magnified images of extended objects are always dimmer than naked-eye images. Second, laser light is coherent and compact, but not stellar. The laser pointer beam entering a telescopic is not intensified as occurs with a celestial stellar object. A Class IIIA green laser pointer does not have sufficient power to siginificantly injure the eye if looked at breifly from a few feet. Telescopic magnfication does not change the energy content of the beam.
Nonetheless, the precautionary principle suggests caution should be used with these consumer products to avoid inadvertent strikes of star party participants. As noted above, there has been no industry or medical study of the combination of green laser pointers and common medications that have photosensitivity as an adverse effect. In the absence of scientific evaluation of those combination effects, the most ethical course of action for amateur astronomers is to exercise reasonable caution to avoid inadvertent laser beam strikes of the eye pupils of participants at star parties.
The FAA used ambiguous descriptions in a study describing presentation pointer's nominal visual hazard zones4 for FDA regulated Class IIIA lasers. The FAA nominal hazard zones include the "blink" zone, the "flash blindness" zone, the glare effect zone and the "no-effect" zone. The "blink" zone is termed the averted vision zone here.
The effects I experienced by distance and FAA effect zone were:
At distances greater than 500ft (152 meters), laser pointers present a lower effective risk to distant and moving targets than their users might expect, because the coherent light of a green laser disperses to a faint disk and is so difficult to align directly with the optical axis of an observer's eye pupil. Typically users have experience with the tight, easily aimed beam of a presentation pointer at distances of less than 100ft (30 meters). Those user experiences do not directly extrapolate to larger distances.
At 500ft (152 meters) to 1000ft (304 meters), it took about two minutes for a semi-skilled amateur to aim a Class IIIA presentation pointer beam nearly down an observer's eye pupil, using a presentation pointer strapped to and aligned with a tripod-mounted and fine-focuser-directed 20x70 binoculars. Even with those targeting aids, at those distances and as the targeted observer, I still had to align my eye pupil directly along the optical axis of the pointer's beam to experience a glare effect.
At night, where object distances are greater than 500ft (152 meters) and the background of the object is the night sky, pointer users have a difficult time acquiring a stationary, unlighted or lighted, non-reflective target. Aiming a pointer under those conditions is difficult because a distant well-lit visual reference point is needed for effective eye-hand coordination. A lighted objected provides a visual reference point at which to aim an laser. But even then effective eye-hand coordination does not occur unless the object is reflective. Without reflectivity, there is no feedback that the presentation pointer is illuminating the object and eye-hand coordination does not occur. At distances of less than 100ft (30 meters), the bright disk of the pointer provides a distant reference point against which the observer's eye-hand coordination can act. At distances greater than 500ft (152 meters), the terminal disk of the pointer's beam is not visible to the naked-eye or in binoculars, where the background is the night sky. The beam simply disperses in the distant, atmospheric background. The observer cannot coordinate their eye and hand. Unless the pointer's beam creates a distant, terminal disk by striking a reflective surface, accurately targeting faint objects at distances between 500ft (152 meters) and 1300 ft (396 meters) is extremely difficult, even where the object is stationary and locating aids like binoculars are used.
A simple experiment illustrates the difficulty of accurately aiming a pointer at a distance of 1000 ft (304 meters) by an angle alone and without the benefit of being able to coordinate the hand with a distant visual point of reference. Hold a raised index finger outstretched at arm's length and sight down the middle of your fingernail. Using your other hand, hold a pen about four inches from the fingernail of your other outstretched hand. Point the pen at the middle of your fingernail. Now move the pen so it points at the left or right corner of your fingernail. This pointing movement is about 1/2 a degree. At 1000 ft (304 meters), the corresponding linear movement of the end of a pointer's beam would be about 9 feet (2 3/4 meters).
Paradoxically, inadvertent eye pupil strikes are easy to produce at distances of 1000ft when a green presentation pointer is coupled as a finding device to telescopic mount. Telescope mounts suffer from 8 to 30 arcsecs of vibration when slewed or accidentally bumped lasting about 1 to 4 seconds. If a green presentation pointer is attached to a telescope, it too will vibrate. Using a binocular mount setup, at 1000ft, I found mount vibration caused an 18" beam to dance in a several meter circle. Persons standing in the vibration-caused zone will experience annoying momentary beam strikes. They are not hazardous; the effect is similar to the rotating lights of emergency vehicles at night.
A pointer beam easily can be aimed against a hillside at distances of 1 kilometer (3281 feet) (and with more difficulty at 1.5 kilometers (4921ft)) using a hand-held 10x50mm binocular and hand-held pointer. This is because the hillside provides a surface off of which the faint terminal disk of the pointer's beam can reflect. Under those conditions, the observer can coordinate their eye and hand.
I did not view the glare effect of a green laser pointer at distances of 1 kilometer (3281ft) and 1.5 kilometers (4921ft). It is impressive that a pointer's beam can be seen through binoculars projected on a hillside at 1 kilometer (3280ft) and 1.5 kilometers (4921ft). But computations suggest that at those distances, the pointer's beam is a disk about 1 to 1.5 meters in diameter and about 18 magnitudes dimmer, or approximately 0.015%, than its initial brightness.
In conclusion, the visual effects of green presentation pointers cause a only a nuisance hazard to bystanders at distances greater than 1300ft (396 meters). At distances under 200ft (61 meters), the combination effect of consumer laser pointer light and photosensitivity and/or phototoxicity in commonly taken medications has not been researched by industry or the medical community. The FAA blink reflex zone of 51 feet (15.5 meters) appears low. My experience is that the averted vision zone extends out to 200 feet (61 meters). My differing experience may be the result of the Leading Light Technology, Inc. pointer used here. It has lower dispersion than the assumed pointer used in the FAA study. The FAA glare effect zone extending to 1171 feet (357 meters) was similar to the glare that I experienced. Attenuation is significant beyond 1100 feet (335 meters). Glare is much lower as compared to distances less than 1000 feet (304 meters). At 1300ft (396 meters), the residual glare of a green presentation pointer is similar to a car headlight at that same distance on high beam.
Although not a safety hazard beyond 1300ft (396 meters), bystanders at those distances can be inadvertently struck with a faint green light, creating a light-trespass nuisance. A light-trespass can generate conflicts between homeowners and amateur astronomers. The pointer user may not receive naked-eye feedback at those distances that would warn the user of the nuisance that their pointer creates. Like reasonable use of car high beam headlights when driving, presentation pointer users need exercise reasonable caution when using these devices in order to prevent nuisance complaints from bystanders, drivers and homeowners within 1500ft (457 meters).
Responses to this social controversy can be divided by participants, e.g. - personal, user community, industry and governmental responses.
With respect to the personal response, these tests gave me a greater appreciation of the glare effects experienced by persons on the "receiving end" of a green presentation pointer, as opposed to the usual "business end." As a consequence, it increased my commitment to safe responsible use of green laser pointers for astronomy education. Knowing these effects, individual consumers should be aware of the boundaries of FAA outdoor laser display exclusion zones surrounding local airports and avoid that would effect those zones.
These tests also make me question whether, based on the precautionary principle, it is socially advantageous to the amateur astronomer community to use laser pointers as telescope pointing devices, even though the technology may be available and considering existing alternatives. My own personal choice is to not use green presentation pointers for that purpose.
With respect to community responses, one possible action would be for leading amateur astronomical groups to develop a joint statement on safe laser pointer practices during star parties and when observing as an individual. Such a statement could be jointly developed with industry and governmental regulators.
With respect to industry responses, distributors could address the variation in the actual emittance of green laser pointers that are delivered to end-users but that claim to be under the 5mW FDA limit. U.S. distributors can aid end-users by delivering a more uniform product to consumers by adopting voluntary industry standards for 1 millradian dispersion of Class IIIA lasers and by implementing a more aggressive program to inspect and reject non-complying Class IIIA lasers.
With respect to governmental responses, the Federal Aviation Administration (FAA) could better aid astronomical consumer pointer users by recalibrating and republishing its Federal Aviation Administration (FAA) nominal visual hazard zones for Class IIIA pointers specifically for brighter green laser pointers and by subdividing the existing "glare effect" hazard zone2 into two zones - a closer zone where 30% of central vision is impacted (approx. 1300 ft (396 meters) and a farther-fainter glare zone.
The FAA should develop and publish an internet map database that shows overlays of these zones with area street maps in order to aid citizens with complying with obligations under obscure FAA Order 7400.2E. Few citizens will be aware of the extensive dimensions of FAA "sensitive," "critical," and "laser free" zones around local airports. Some relevant zones extend over 10 miles from an airport. Although it is often said that "ignorance of the law is no defense," the FAA does have the obligation to give the general public reasonable notice of it's flight directives, considering the context of the matter, so that citizens can take reasonable steps to comply with the law. General citizens unfamilar with FAA flight operations should not be required to uncover obscure FAA orders in order to comply with the agency's regulations.
FAA Order 7400.2E was originally adopted to regulate the interference of commercial outdoor laser light shows with airliner landing and take-offs. Such shows use a much higher power that is not comparable with consumer Class IIIA lasers. Since FAA Order 7400.2E was originally adopted to regulate the interference of navigable air space from commercial outdoor laser light shows, the Order's suitability as a regulatory tool to address the personal use of Class IIIA green laser pointers is questionable. A new FAA order addressing consumer laser pointer users should be considered.
The Federal Drug Administration (FDA) might improve its regulation of Class IIIA pointers by including an express dispersion criteria of 1 milliradian. This might be implemented in coordination with a revision to ANSI Standard Z-136.1 (2000). Under the current situation, whether caused by manufacturer variations in emittance or dispersion, amateur astronomy consumers cannot reliably use green presentation pointers with confidence that FAA nominal visual hazard zones are at the same distance between pointers made by different manufacturers. The FDA might also use its regulatory power to improve labeling for Class IIIA green laser product inserts. An improved FDA product insert would reproduce the FAA nominal hazard zones in chart form and advise users of the existence of FAA exclusion zones prohibiting the use of lasers around airports. This would give consumers ready access to information that they need to responsibly use these consumer devices.
I am divided on whether at this time, the FDA should require all Class IIIA green laser pointers to be equipped with "dead-man" safety switches. Most Class IIIA green presentation pointers currently sold in the United States have simple on/off push button switches. A "dead-man" switch, which only allows the pointer to project a beam while the operator depresses a button, could reduce the risk of inadvertent strikes. However, that makes the use of such pointers as a telescopic pointer device impractical.
By applying safe practices, amateur astronomers can assure themselves and the public that the educational benefits of these consumer products outweigh their potential social costs.
An am an amateur astronomer and not a medical, physics or optics expert. Therefore, I do not recommend you try to replicate any test shown here. If you do, you do so at your own risk.
A viewer cannot assess the vision risk of looking on-axis at a laser pointer beam. Properly labeled Class IIIA lasers may be defective and emit higher levels of light than stated on the label. A study at Herriot-Watt University which found that 14 out of 17 Class II laser pointers emitted more than their safety-rated levels.2 Many laser pointers marketed as "ultra-powerful" may be emitting unsafe levels that can damage vision.2 Persons of young or advanced age can have a different phototoxic response to bright light than middle-aged adults. You could be a person who is unknowingly using light-activating chemicals contained in dietary supplements, cosmetics, or drugs. These chemicals heighten your phototoxic response to intense light. Exposure to intense light in such persons may lead to permanent loss of vision.34,35 Experience with the brightness of red laser pointers does not directly translate to green laser pointers. The human eye is more sensitive to red light than green light. A green laser pointer of equal apparent brightness to a red laser pointer emits 10 times the energy of a red laser pointer.2 Recent research indicates that green laser pointers may cause retinopathy in severe exposure conditions in less than 60 seconds.32
Government regulations,37 and publications42,43, product literature41 and industry literature5,24 warn against ever viewing a Class IIIA laser beam with binoculars or telescopes.
The product literature41 that came with the presentation pointer used in this informal test states that the useful life of the diode laser will be reduced if it is left on for more than 3 minutes.
I did not try to use an astronomical digital camera to make photometric measurements and have no well-formed opinion on the risk to their photosensitive chips if such cameras are exposed to laser light. I used a film camera, not a digital camera.
After-image: "The perception of light, dark, or colored spots after exposure to a bright light that may be distracting or disruptive. Afterimages may persist for several minutes."2
Averted-vision response: "Movement of the eyelid or the head to avoid an exposure to a noxious stimulant, bright light. It can occur within 0.25 seconds, and it includes the blink reflex time." OSHA Manual 2005, Appendix III:6-5, Glossary of Laser Terms.43
Blink reflex: See "averted-vision response".
Class I laser: "Class I levels of laser radiation are not considered to be hazardous." 24 C.F.R. 1040.10(a)(5) ftn. 1 (amended March 31, 2000).37
Class II laser: "Class II levels of laser radiation are considered to be a chronic viewing hazard." 24 C.F.R. 1040.10(a)(7) ftn. 3 (amended March 31, 2000).37 "Class II lasers are] low-power visible lasers that emit above Class I levels but at a radiant power not above 1 mW. The concept is that the human aversion reaction to bright light will protect a person." OSHA Manual 2005, sub paragraph IV(b)(2)(c).43
Class IIA laser: "Class IIa levels of laser radiation are not considered to be hazardous if viewed for any period of time less than or equal to 1x10^3  seconds but are considered to be a chronic viewing hazard for any period of time greater than 1x10^3  seconds." 24 C.F.R. 1040.10(a)(6) ftn. 2 (amended March 31, 2000). 37
Class IIIA laser: "Class IIIa levels of laser radiation are considered to be, depending upon the irradiance, either an acute intrabeam viewing hazard or chronic viewing hazard, and an acute viewing hazard if viewed directly with optical instruments." 24 C.F.R. 1040.10(a)(8) ftn. 4 (amended March 31, 2000). Lasers within Class IIIA are further subdivided into two categories: those with outputs less than 2.5mW, which must bear a "Caution" sticker, and those with outputs greater than 2.5mW but less than 5mW, which must bear the "Danger" sticker. 24 C.F.R. 1040.10(g)(2)(i)-(ii) (amended March 31, 2000).37
Class IIIB lasers: Class IIIb lasers can have an emission level up to 100 times that of Class IIIa lasers. "[Class IIIb lasers] are considered to be, depending upon the irradiance, either an acute intrabeam viewing hazard or chronic viewing hazard, and an acute viewing hazard if viewed directly with optical instruments." 24 C.F.R. 1040.10(a)(8) ftn. 4 (amended March 31, 2000).37
Flash blindness: "A temporary vision impairment that interferes with the ability to detect or resolve a visual target following exposure to a bright light. This is similar to the effect produced by flashbulbs, and can occur at exposure levels below those that cause eye damage. This impairment is transitory, lasting seconds to minutes . . ."2
Glare: "A reduction or total loss of visibility, such as that produced by an intense light source, such as oncoming headlights, in the central field of vision. These visual effect lasts only as long as the light is actually present . . ."2
Milli- Micro - Nano: The metric system has prefix modifiers: Milli. m. 0.001. Thousandth. Micro. u. 0.000001. Millionth. Nano n. 0.000000001.
Precautionary principle: "The precautionary principle . . . is the idea that if the consequences of an action are unknown, but are judged to have some potential for major or irreversible negative consequences, then it is better to avoid that action. . . . . The substance of the precautionary principle is not really new. The essence of the principle is captured in cautionary aphorisms such as 'An ounce of prevention is worth a pound of cure', 'Better safe than sorry', and 'Look before you leap'." Wikipedia. Precautionary Principle. http://en.wikipedia.org/wiki/Precautionary_principle accessed 10/25/2005
Relative or apparent magnitude: The measurement of the apparent brightness of a distant object, using the brightness of another object as a reference. See "Apparent brightness" at Wikipedia, an online encyclopedia.
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K. Fisher firstname.lastname@example.org (Org. 10-27-2005, Rev. Nov. 4, 2005)