Recent months have seen increasingly frequent comments in one place or another about laser pointers and allusions to their engendering "Laser Rage" presumably when an unsuspecting member of an audience gets dazzled by a flash in the eye or perhaps triggered just by alarm that a "laser beam" is being used carelessly. Probably part of the reason for the increased publicity is that such gadgets have become much more commonplace than formerly, since prices have dropped to the point where they are available for under $50 in Canada and probably under $20 in the US. What was formerly an executive's toy has become a trendy trainer's tool AND, rather more significantly, something that a parent might consider to be a suitable gift for a science oriented child. And there's probably the biggest rub!
It is a simple fact that the present crop of such devices CAN EASILY produce exposures in excess of recommended limits particularly in the hands of an unsupervised youngster. And it is hard to imagine an effective laser pointer that would not do so.
Arguments of practicality appear to have resulted in a blind eye (no pun intended) being turned to such devices being used in an unrestricted or unregulated manner where comparable sources in occupational situations face rather strict administrative and engineering controls that, to date, have been rather meticulously and thoroughly enforced by "responsible" corporate citizens and government agencies entrusted with worker and consumer protection. One is tempted to speculate on whether the result of trends toward a deregulated society might not be leading to an unregulated society and whether the promised benefits of reduced costs (and hence prices) and increased efficiencies are going to be traded for increased risks and damage to health and well-being.
At the risk of raising unnecessary alarms, let's review what the standards and guidelines controlling lasers and exposure to emissions from lasers entail.
What has been put into place is a classification system for lasers which identifies the level of risk associated with them. Simply put there are four classes.
Class 4 lasers are the most dangerous. Regardless of wavelength (colour) ANY exposure (NO MATTER HOW SHORT THE DURATION MIGHT BE) to direct or reflected beams WILL produce serious damage to the skin or eye - PLUS - diffusely scattered emissions from objects or materials irradiated (illuminated) by the beam can be hazardous. In addition there are secondary risks such as those associated with igniting flammable materials or secondary damage from shock waves arising from pulsed exposures, for example. Deciding whether or not a laser belongs to Class 4 is easy. If it can put out more than 500 mW it is a Class 4 laser. A Class 4 laser must carry a label stating "DANGER, Avoid Skin or Eye Exposure to Direct or Scattered Beams."
Class 1 lasers are the least dangerous. Regardless of wavelength (colour) any exposure (EVEN FOR THE LONGEST PRACTICABLE DURATIONS) to direct or reflected beams is not expected to produce any damage to any tissue or material although it must be recognized that good data is not available to permit extending that assurance to chronic, long term, low level exposures. Deciding whether or not a laser belongs to Class 1 is not particularly easy principally because the biological end point forming the basis for establishing limits varies across the optical spectrum. As a result one has to consult rather complicated tables like the Threshold Limit Values (TLVs) of the American Conference of Governmental Hygienists (ACGIH) or similar tables, possibly within regulations, published by other organizations, which have been developed to summarize the salient biological effects data for each spectral region. What it comes down to is that for the ultraviolet and visible portions of the optical region the laser output has to be less than fractions of a µW to belong to Class 1 (roughly a million times less than the Class 4 limit). This arises from the fact that ultraviolet radiation can induce photochemical damage (erythema of the skin and damage to superficial ocular tissues) at very low levels while in the visible region concern shifts to thermal damage of retinal tissue where the focussing power of the eye acts to render hazardous, levels that would otherwise be inconsequential. In the near infrared concern continues to reside at the retina because the ocular media remain relatively transparent but since the focussing abilities of the eye decline any incident energy cannot be focussed as well and consequently higher outputs ranging to 10s and 100s of µW depending on wavelength are permitted in Class 1. And finally, in the middle and far infrared, outputs ranging to 10 mW are permitted in Class 1 because the only consideration is substantial thermal damage to the skin. Class 1 lasers are not required to carry any label at all.
Thus, to summarize, Class 4 lasers are unequivocally and undeniably damaging while Class 1 lasers are not known to be capable of producing any permanent damage. Therefore all other lasers are somewhere in between these two extremes and essentially that is what defines Class 3 lasers. They ARE capable of producing permanent damage but only under certain conditions, e.g. combinations of exposure intensity and duration, certain combinations of exposure geometry, proximity, environmental factors, etc. Most simply put, under typically assumed possible exposure situations, Class 3 lasers can produce skin or eye exposures in excess of recommended limits before you can react.
"But, wait," you say, "what about Class 2?"
Well it turns out that there is a Class 2. However, it turns out to be a subclass of Class 3, not really a "different" Class. Class 2 represents the first concession made to the relatively simplistic triage represented by Classes 4, 1 and 3. Class 2 exists because humans have built-in detectors, i.e. our eyes, for a portion of the optical spectrum, viz. the visible portion. If we could not "see" the emissions from lasers like we can't see ultraviolet or infrared or the beam from a microwave antenna, Class 2 would not exist. Because we can "see" in the visible region it is assumed, in the process of setting permissible limits, that we will respond if appropriately informed or trained. Therefore, in the visible region, Class 2 is interposed between Class 1 and Class 3 on the assumption that a person can and will respond upon "seeing" the laser output. Outside the visible region there is nothing to respond to so that no response is assumed and there is a direct transition from Class 1 to Class 3. For Class 2, the permissible output level is raised from fractions of a µW to 1 mW WITH THE PROVISO THAT the laser carry a label stating that it is a Class 2 laser and the statement "WARNING, Do Not Stare into Beam." What is the assumed response? It is very simply that the person will close his eyes or avert his gaze. Why a limit of 1 mW? Well, the action of closing one's eyes upon perceiving a bright light (or reacting to any other threat to the eyes) is called the blink reflex and nominally takes 250 ms to occur. Therefore, a 1 mW laser acting for 250 ms will deliver 250 µJ to the retina and research has shown that this is roughly the threshold beyond which the risk of producing permanent retinal damage becomes unacceptably high. Consequently, in the visible region, Class 3 lasers are those which can deposit unacceptable amounts of energy into the eye faster than one can blink and even Class 2 lasers can do so if one chooses to override the blink reflex and STARE into the beam.
Well, surely the preceding must be enough background material on laser classification to allow us to turn our attention, at last, to laser pointers.
Unfortunately, there is one more wrinkle in the classification system to deal with. It turns out that in the visible region, what remained of Class 3 after Class 2 had been established was further subdivided into two classes; Class 3a and Class 3b, the boundary being at 5 mW output. This was done to reduce the burden of administrative and engineering controls applicable to Class 3 lasers for systems using the laser in such a way as to keep the beam moving rapidly from one point to another at all times. The best example of this is a system used for installing ceilings where the beam is projected onto a rotating mirror to establish the level at which hangers are to be placed. As long as the mirror is rotating, the beam cannot illuminate any given point for more than an instant at a time and typically the system incorporates an interlock to ensure the laser beam is turned off should the mirror stop rotating.
NOW, finally we are in a position to turn our attention to laser pointers and ask whether or not we should be worried about them and, if so, what kinds of things we might reasonably worry about. Let us do so by assuming a laser pointer based on each class in turn and considering first whether it would be effective for the purpose at hand and second what kinds of exposure situations might we realistically envisage as being associated with each. We will also assume the laser operates in the visible region although one might envisage special systems using lasers operating in the ultraviolet or infrared where the screen might be treated in some way or otherwise designed to produce a visible indication of the spot being irradiated by the laser.
First let us assume a laser pointer based on a Class 1 laser.
This would be ideal since such a laser pointer would be totally incapable of producing any damage to skin or eyes from any practicable exposure scenario. As a Class 1 laser, no labelling, training or information would be required and one could rest assured that any conceivable use including unrestricted and unsupervised access to and use by children would be acceptable. Because scientific data for long term, low level exposure situations is lacking, the only worries that might arise would be from exposure situations where one would envisage very, very long exposure durations extending out to hours or days at a time or possibly somewhat shorter exposures repeated many, many times. This sort of "worry" is clearly a bit of a stretch since long term, low to moderate and even occasional high exposures to optical radiation are an integral part of day-to-day life. Only if there were some peculiar, so far undiscovered, biological effects connected with the spectral purity or coherence of the output from lasers might there then still remain some residual uncertainty about the complete safety of a Class 1 laser pointer.
So, why not restrict laser pointers to Class 1 lasers? The short answer is simply because they would not be very effective.
Even though a Class 1 laser will be quite bright if you look directly into the beam (see Note 1), the most it could project into a spot on a screen would be a fraction of 1 µW. Such a spot would be quite easy to see in a fully darkened room. BUT, in typical situations where a slide is projected onto the screen or ambient light levels are increased so that members of the audience can see to take notes, the visibility would be reduced to the point where the illuminated spot would be difficult or impossible to see. The effect is identical to that of not being able to see the stars during the day because their light is overwhelmed by the brightness of the sky. Similarly, Class 4 lasers have been used in light shows outdoors and, despite their being over a million times more powerful than Class 1 lasers, are only effective at night when ambient light levels are reduced.
Thus, in order to be effective, it is clear that a laser pointer has to use a laser above Class 1.
So, let us assume a laser pointer based on a Class 2 laser.
A quick look at the properties of Class 2 lasers shows immediately that the situation is now LESS THAN IDEAL for a number of reasons but most simply because one can easily envisage practicable exposure scenarios where exposure limits can be exceeded. Granted, when properly used by properly trained or informed individuals there is very little danger to anyone. However reactions of alarm or distress should not be surprising from careless or thoughtless use such as needlessly pointing into an uninformed or otherwise unprepared audience. Even a Class 1 laser might elicit such responses simply because a "laser beam" was being flashed around indiscriminately. Of course regulations require that such a pointer carry a label stating that it is a Class 2 laser and the warning "Do Not STARE Into Beam." To review, as a Class 2 laser, it is capable of creating an exposure exceeding recommended limits in as little as 250 ms. As a result there are many worries one might have about the unrestricted use of such devices, especially when one envisages unsupervised use by children. A responsible user (see Note 2) would be expected to heed the label and indeed not stare into the beam. For an unsupervised child, one might worry that such a label would be an invitation to TRY staring into the beam. A responsible user would avoid pointing the beam needlessly into the audience or at any person and particularly not into someone's eye. In fact, to preclude any possible overreactions or claims from members of the audience a judicious user might well announce that a Class 2 laser pointer is being used and that should a direct or reflected beam accidentally enter the audience, even one's eye, the consequence is no different than from a camera flash lamp. In any case it would be almost impossible under normal circumstances to hold the laser pointer steady enough to illuminate someone's eye for longer than 250 ms. For an unsupervised child, such "targeting" of objects and people is almost certain (see Note 3). However considering how difficult it would be to hold the beam on anyone's eye for more than 250 ms under such circumstances there is no real risk of any damage to anyone from such playing around.
So, if laser pointers are to be effective we must accept that they use Class 2 lasers. And the only real worry is that of unsupervised use by children. A situation somewhat comparable to what exists for other potentially dangerous things such as power tools, kitchen appliances, knives, axes, firearms and such - not totally unreasonable. Where the user may be a child we assume a responsible adult will make clear what the dangers are and take suitable precautions to ensure the child's safety. The only remaining "worry" is that hardly any adult has personal experience with or knowledge of lasers that is in any way comparable to what they would be expected to have with other dangerous things that a child might encounter. In fact the executive, trendy trainer or doting parent who decides to allow a child easy access to such a laser pointer might dismiss the warning as overkill, seeing the device as nothing more than a fancy flashlight particularly with it being powered by only a couple of small batteries. Ideally, as a bare minimum, the instructions provided with Class 2 laser pointers should contain the gist of the preceding information by way of "training" the user. Whether this situation warrants any specific action is debatable. In a laissez faire, deregulated (unregulated) society it might be tolerated. In a highly regulated and protective society it would probably not be tolerated.
So, that's the end of it, isn't it? While laser pointers using Class 2 lasers might be dangerous, they are not really that different from other dangerous things to which children are exposed.
Unfortunately, that is NOT the end of it. There is still more to the story. It seems that a horsepower race has started and Class 3a laser pointers are beginning to appear. They can produce exposures in excess of permissible limits faster than you can blink, in as little as 50 ms. Presumably they are not banned from sale because it is hard to conceive, under normal conditions of use, that the beam could be directed into a person's eye, by hand, steadily enough for even that length of time. While that is probably true, all the other worries about unsupervised use are exacerbated for only a minimal gain in performance of the laser pointer allowing it to be used effectively in somewhat brighter ambient lighting conditions. The question becomes just how much risk are we prepared to impose on the untrained, uninformed or unsupervised users for the sake of having marginally more effective laser pointers.
To date there are no reports of Class 3b laser pointers except in military targeting applications and there it's not a question of safety, except for the good guys, of course. Assuming such devices never appear commercially then that's pretty much the end of the story. Class 4 laser pointers would be tantamount to using a bazooka or flame thrower as a pointer and again except for the military pretty much outside the realm of normal society.
1 µW at 683 nm - a Helium/Neon laser - represents 3.4 X 1015 photons per second entering the eye. By comparison, the sun delivers, in the visible range, about 100 times more, i.e. 277 X 1015 photons per second and the faintest stars you can see at night - about magnitude 5 - deliver about 68,000 photons per second in the visible range.
It is not too long ago that two adults who should have known better - a lighting technician and a TV cameraman - severely damaged a very expensive camera experimenting with a Class 4 laser. Both were very lucky not to have been seriously injured. Neither had been adequately trained as to how risky their experimentation was and why. Consequently they were also putting at risk other studio personnel, performers and audiences. They, having observed that the newest cameras could be pointed directly at the sun without suffering any damage, reasoned they should be able to do the same with a Class 4 laser they were using for some special effects. What they didn't realize was that the laser was effectively 1,000 or more times as bright as the sun and as result ended up destroying the image detector array.
In fact, the author experienced such an incident 25 years ago on a residential street in Ottawa. Upon noticing the red spot dancing around on the side of his body and starting to look around for its source, it disappeared. If it had illuminated the eye, it would have been possible to estimate where it had come from but, as it was, it was impossible to tell. The author was quite prepared to chew somebody out (possibly one of the first occurrences of "laser rage" although the author wasn't really in a rage) particularly if it could be determined that it was not a Class 1 or Class 2 laser that had been used. However, despite walking back and forth to check out the windows of the three or four houses it might have come from there was nothing obvious and, since nothing drastic had occurred, knocking on doors seemed superfluous. It was assumed that if it had been a youngster or even a government technician fooling around, he or she was probably cowering in fear of being found out and put upon. It never happened again although the author continued to watch out for that red spot along that stretch of the street for several weeks after.
A.M. (Tony) Muc, Ph.D.
Radiation Health and Safety Consulting