The Danger Of Green Laser Pointers

The problem, as they mention, is there may be an unknown amount of infrared radiation emitted by the green laser, which is potentially very harmful.

Their test method is a bit awkward: It involves shining the laser light off a cd, and having the reflected light (a diffraction pattern) shine on a piece of white paper, then photographing (or observing) the diffraction pattern with a digital camera that is IR sensitive or in which the IR filter has been removed. (Would you do that with your expensive digital camera??)

A much cheaper and simpler test (though not a 100% guarantee) is, in a dark room, to shine the laser on a standard night light that has a built-in photosensor (typically a CdS or CdSe photoresistor). And see if the laser turns off the night light. Then put a red filter over the laser (like Rubylith film or Rosco #27 Red polyester film) and see if the night light still turns off when you shine the filtered laser light on it. If it DOES, then the laser is emitting a lot of IR. Note that some night lights are not sensitive to IR; you can determine this by using the red filter over the night light and seeing if the night light turns off when the room lights are turned on.

Years ago when these hand held lasers first came out, we were discussing how bright they are and how damaging they could be. One colleague suggested shining it on the ground where the sun was shining. If you can see the light it is more intense than the sun (and you can see it), and only a dummy stares at the sun (cos he can't damage his eyes) so don't stare at the laser light unless you're a dummy.

I am stunned that such a poorly documented article could be cited here on an engineering blog. With the exception of mentioning the initial infrared laser diode output power of 10 microwatts and the specific frequency changing done to make it a green light there is nothing ever mentioned about which frequencies, power levels, radiance, irradience or confocal characteristics are considered hazardous. For those interested in these parameters, OSHA STD 01-05-001 does publish them. But not only does this article never mention what is considered dangerous, they don't present any valid quantitative measurements on the light any laser pointer produces. The only thing they do is accuse the unnamed manufacturers of criminal activity for removing filters they think are required. Oh excuse me, they do propose a crude use of a "web-cam" and a Compact Disc for a diffraction grating to detect any infrared light produced. I'm certain that the anonymous authors of this article did not identify which manufacturers they felt were criminals so that they could not be charged with libel themselves.

Have you ever stood under a multi-hundred-watt infrared heater? It felt nice and warm, no doubt, but did it fry your eyes?

(mW should be milliwatt; μW would be microwatt.)

Even if you can't see the infrared, I would think you could feel any harmful level. I may be wrong about this, but I agree that the article was extraordinarily poor.

Pardon me. Did you say "can emit dangerous levels of infrared radiation"?

My car heater emits a great deal more infrared radiation (that would be "HEAT", which is what it is MADE to do) than any battery-powered pocket laser.

Shoot, my household furnace does that, WAY more, even than my car does.

My fireplace emits all kinds of radiation, both infrared (non-visible spectrum radiation) and visible light (admittedly, that tends to shift toward the red end of the spectrum also).

Neither of those is a dangerous source of radiation (though I have got the home version of a sun-burn from my fireplace, on occasion).

I think whomever decided to post this to CR4 should be examined for radiation burns, or something similar, from leaving their aluminum hat off too long.

And perhaps, those of us who read between the lines can see that the level of radiation emitted COULD be dangerous, to the naked eye, when looking directly into the beam.

But that applies to any laser product, of any power output high enough to perform any work.

This isn't science. Its axe grinding.

I am answering you and Redfred:-

Thanks to you both for bringing some sense to this blog.

If the IR levels were SO dangerous, then a simple IR blocking filter would have overheated fairly quickly I feel......

What would be a good way to decide if a pointer was REALLY dangerous (always dangerous for eyes anyway...!), is there a simple method?

Well, though the subject it "Green Lasers", I think the below suggestion could apply to any quasi-coherent energy emitter, with particular application to any laser, or quasi-lasing device, which would include the pocket "laser" diodes (not true lasers, but the subject of this discussion, and the seeming immediate source of the greatest danger).

I think it would have to be a combination measurement of a) propagation pattern, b) intensity of impinging energy at some specified distance, and c) wavelength/bandwidth of emitted light (of course, given the coherency of a laser, bandwidth hardly accounts for much, but I think that what we have taken to calling "lasers", which are in fact only relatively coherent emitters, not pure emitters, such as true lasers, can have a relatively wide bandwidth, and possibly even a "dirty" signal, such as one with a lot of RF noise riding on the beam. So, bandwidth becomes a consideration.), somewhat akin to the methods of quantifying dangerous noise levels from speakers.

So, the measurement might be something like "Light pressure level at such-and-such distance from the emitter, on center, and at the such-and-such distance from the emitter, at such-and-such angle off center", with the measurements expressed at various points across the emitted spectrum. Throw in a "random wavelengths" measurement, perhaps expressed as "total visible noise" to include an bandwidth deviations. This would account for any propagation shape, and for any power output, both at known frequencies and at random noise levels, while affording the less-than-technical user/buyer a readily understood method of understanding what danger a particular model might present in a broad variety of possibly, though unintended, uses.

The OSHA safety standard that I offered earlier shows that there are a lot of complicating factors to say that a particular light source can be dangerous to an eye. The earlier description on laser intensity and sunlight is a good touchstone for laser safety. Any light source that can be seen reflected off of a surface sitting in broad daylight must be dangerous to stare at because one should not stare at the sun.

So what's a person to do that needs to use a brighter than daylight light source? Well take some responsibility and don't point it directly into somebody's eye for a long period of time. If you're using a laser pointer in front of an audience, release the button when not pointing to something. This will also save your batteries. If you briefly, accidentally point a laser into the crowd, don't worry about it. Our eyes do regularly get brief flashes of very bright light. Remember that flash photograph that left a lingering bright spot in your vision.

I agree that those measurements and cautions all work for the everyday user, and SHOULD be carefully applied in all uses.

I thought you were asking "How would I specify the power output of the laser, in comparison to danger levels for similar things?" Obviously a different kettle of fish altogether, and my misunderstanding. I apologize for my obtuseness.

If your car heater emitted the concentration of power per area that these lasers put out I think you would be well done real quick. Something like this is not going to fry your entire eye, just burn out little spots on your retina. You don't mind a few blind spots do you? These lasers do not put out much power but they are REAL concentrated.

According to the OSHA document the spot size from a pointer would be on the order of 17 micrometers on the retina. The area covered would thus be A = pi*r², or 2.27 x 10^-10 m².

According to the article above, the frequency-doubled (1064 nm) output of an inexpensive green pointer laser can be 10 times higher than the rating of the 532 nm limit, so since the laser was rated at 10 mW, they must have measured 100 mW from the cheap green laser (or at least, that is the potential output they infer).

Taking these two values together, the implied intensity of the 1064 nm energy on the retina would be 100 mW in an area of 2.27 x 10^-10 m², or 440 MW/m². [MW as in Megawatts per square meter.] That's a heckuva lot high energy flux than the output from a car heater or fireplace.

If the spot size claimed by OSHA is correct (and it seems likely) and if the IR output is as large as the researches claim, then YES the unfiltered IR output from a green laser pointer could do some damage to a person's retina.

I do think the researchers are exaggerating the danger, nevertheless it is wise to take some simple precautions and to be aware of the invisible danger.

I somehow think that we are diverging away from reality here.

Firstly, its simply not a good idea to look at any laser pointer, or shine it into someone else's eye either......even ones at less than 5mW...it should be the same rule as for pointing "unloaded" guns at people.....

Secondly, what are we talking about now with regard to 100mW, from a small battery powered LED laser pointer? If true, surely the batteries would have an alarmingly short lifetime?Could I not burn my name on a piece of paper/wood?

Even the ones with an IR filter would quickly burn/overheat the filter (its only a bit of coloured plastic!), if that was true..... (I have mentioned this before!). I have not heard of any with the filter suddenly going up in smoke or anything like that......

In fact, why would any manufacturer want to block IR at low levels? I would be amazed that anyone would bother for a pointer.....

I personally believe that even a properly made 5mW model could possibly damage your eyes as they (human eyes) are very, very sensitive to light, I have accidentally been "flashed" at a distance of a hundred yards or so with a red laser pointer, it was still VERY bright!!! Closer I would not like at all!!!

.....but the possible levels bandied about here do not make sense to me personally from a battery powered unit.....if it does not pop a balloon/burn paper etc., then it is not the levels bandied about. Has anyone tested that?

In a way, I like the idea about comparing a laser with sunlight, which is the brightest, but as I mentioned before, NOT being able to see it in sunlight, still does not make it "eye safe" to my mínd.....what do you Guys think?

Good points Andy.

No laser light of any magnitude or hue should be pointed into another persons eye unless its part of a physician's well controlled diagnostic or surgical procedure. Your comment though of your own brief accidental exposure to a red laser pointer light brings to my mind a few aspects of the OSHA safety standards and how the author of the original story made the green laser pointer more dangerous. Part of the basis of the OSHA standard is the blink response we have to a sudden bright light. By subjecting that laser pointer to a diffraction grating the author was actively removing the safeguard the laser pointer had because the infrared and green light now were taking significantly different paths. An eye along any of the infrared only paths would not blink in response to a bright green light.

First, let me apologize for replying while ignorant, earlier. I know there is no legal citation for this, but perhaps there should be. After all, we do cite, and penalize, for DWI. So perhaps RWI should be a legal infraction, also, since it can undoubtedly do damage.

Second, thank you for enlightening us so thoroughly on the subject, and, though the original article WAS badly written (it left us all in the dark), helping us to see the real problem.

Third, in light of the above, which is surely MY opinion, GA to you, sir. Please, even late, bring your two cents, especially when your two cents are of so much more value than mine were.

Yes, your anecdote certainly does deserve a GA. It is much more informative and practical than the original article. I'm particularly glad to hear that your luck held out during that drive so you could bring your story to us.

Welcome to the madhouse.