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Laser Safety

You Only Received One Set of Eyes...Protect Them

Lasers are unique in their safety hazards, particularly to something you value highly - your vision. While the dangers of firearms and explosives are obvious to most sane people, the possibility that a stream of massless photons even from a low power laser can cause instant severe and irreversible damage to vision or even total blindness is something that often needs to be stressed and restressed.

Lasers have tended to be high glamor devices popular with with hobbyists, experimenters, entertainers, and serious researchers alike. However, except for very low power lasers - those with less than a fraction of a mW of beam power - they do pose some unique hazards particularly with respect to instant and permanent damage to vision.

There are several reasons that even small lasers which do not represent any sort of burning or fire risk can instantly and permanently damage vision:

The output of many lasers is a nearly parallel - highly collimated - beam which means that not only is the energy concentrated in a small area but the lens of the eye will focus it to a microscopic point on the retina instantly vaporizing tissue in much less than the blink of an eye. A collimated beam represents the rays from an object at infinity so if your eye is focused for distance, the laser will be in focus as well.

A cheap laser pointer produces a highly collimated beam. Even at power levels considered relatively safe, one shouldn't deliberately stare into the beam for any reason. For these relatively low power lasers, permanent eye damage is not that likely but why take chances?

As another point of reference, the mid-day Sun at the Earth's equator on a clear day has a power density of about 1 kW/m2 or about 1 mW/mm2. It would not take very long staring into the Sun to burn out your eyeballs! (Yes, I know, some people have claimed to do this all day without harm - I wonder what a vision test would reveal?) Also see the additional comparison, below.

While laser pointers themselves may not be quite as dangerous as some people may have you to believe, that such macroscopic effects can take place at these relatively modest power levels should provide some additional respect for the damage that can result under just the wrong set of conditions.

Laser safety is no laughing matter.

A 1 mW laser has the potential to produce an intensity on the retina 167 times that of direct sunlight! But there are many more factors to consider in determining the real risk of damage. In addition to those noted below, the actual focal point when looking at a laser at close range will not be at the retina so the spot size will most likely be much larger.

Even if the spot from the Laser beam is smaller, natural eye movements or movement of the source (e.g., some moron waving a laser pointer) will result in it hitting any given point for a shorter time than the larger spot from the Sun (which usually doesn't move very quickly).

But, at least, perhaps you'll now have a bit more respect for that little laser pointer!

Problems With Determining Safe Limits
Since you likely did only receive the standard single (1) pair of eyeballs and replacement isn't yet feasible (or covered by major health insurance plans!), trying to figure out if your laser is a hazard to vision by staring into its beam is a really really bad idea. Many factors can result in it being way to late before you discover that your vision has been harmed.

Note that even a wavelength considered eye-safe like 1,500 nm (1.5 um) is only safe in the sense that this light won't penetrate to the back of the eye and be focused on the retina. A high enough power density can still obliterate the cornea and/or lens!

The blink reflex comes into play for visible sources.
If you're smart, you don't stare at the Sun, and you don't stare at other intense light sources - visible or not.

A 1 mW diode will probably not cause damage if you briefly look into it, but I wouldn't encourage you to try it. While it probably won't do anything bad, it is not good to become comfortable with the idea of checking the operation of lasers by looking into them.

Be aware that eye damage that is localized to a small area of the eye is not very noticeable. A laser wouldn't necessarily have to make you totally blind; it could just wipe out a teeny patch here and a teeny patch there. This kind of damage would be very insidious; each time you'd say "Wow! That was bright! lucky I didn't get blinded" - while slowly and cumulatively losing your sight...

General Laser Safety Guidelines

Never look into the beam of any laser. Distance alone isn't a guarantee - some lasers maintain a tightly collimated beams for 100s of feet or more. Specular reflections (from shiny surfaces like glass and metal) may be just as dangerous as the raw beam.

There have been some recent articles about eye injuries resulting from careless or malicious use of common laser pointers. Although the potential for eye injury is typically what comes to mind when one thinks of a laser, the possible side effects - or collateral damage - that may result from aiming one at somebody is at least as likely a cause for the current wave of hysteria.

Actual substantiated instances of long term or permanent effects on vision resulting from momentary or unintentional exposure to a laser sight's beam - or even from prolonged intentional misuse - appear to be all but non-existent. Flash blindness IS possible, but this is temporary and will clear up on its own.

The above applies where the laser pointer has been manufactured and tested to meet CDRH Class IIIa safely limits or below. Note that where these devices originate from countries with less rigorous quality control or where an internal current adjust pot can be twiddled or even if run at very cold temperatures where laser diode output power is greater, to risk of eye damage from intentional abuse, at least, may increase. This is one instance where purchasing your laser sight from US Lasers will be beneficial to you. All laser products that are produced for the US consumer are regulated by the FDA.

With respect to direct personal danger, potential damage to vision is the only real consideration - there is no risk from radiation or enough power in a beam of less than 5 mW to burn anything. However, from a public policy and regulatory perspective, there are actually three areas of concern:

Flash blindness from momentary exposure or permanent damage to vision from prolonged intentional misuse. Laser pointers are usually rated Class IIIa or less which means that the power is low enough that the eye should be protected from permanent damage by natural pupil contraction, blink, and aversion reflexes.

Distraction and collateral damage - you wreck your car because someone pointed a laser pointer at you while you were driving.

Misinterpretation of intent - you get blown away by someone with a BIG gun who thinks you are targeting them with a laser sight. Or, you are arrested and thrown in the slammer for aiming a laser pointer at a cop (this has happened ).

Such behavior should not be tolerated. However, in the remainder of this section, I only really want to address the vision issues.

While I absolutely agree that intentionally aiming a laser of any kind into someone's eye is basically stupid (unless you are having laser eye surgery), one must be careful in interpreting the meaning of press reports that describe momentary exposure to the beam from a laser pointer waved around an auditorium resulting in instant total loss of vision. This is simply not possible.

One would have to direct the beam into the pupil of the eye from a close distance for a few seconds or more without either the eye or pointer moving, twitching, or blinking. Distance is significant both because even laser pointer beams diverge (especially cheap ones) so less energy is able to enter the pupil of the eye as the source moves further away and it is harder/less likely for it to remain stationary and centered on such a target a few mm across.

This is not really possible by accident and even takes significant effort to do intentionally since the eye's natural pupil contraction, blink, and aversion reflexes will prevent the beam from focusing on a single spot on the retina with a sufficient concentration of energy for more than an instant - not enough time for damage to result.

There would have to be cooperation which can only really happen in a game of chicken - but it is hard to protect people from their own stupidity. This does mean, however, as if it isn't already obvious, that laser pointers should be kept from infants - period, and away from children unless adequately supervised. Adults, on the other hand, presumably know not to stare into painfully bright lights and some may even read the warning labels!

Though momentary exposure may indeed result in temporary flash blindness, disorientation, multiple afterimages, and a headache, such effects, while not to be minimized in importance, should not be permanent. And, as the distance between the eye and the pointer increases, their severity and duration diminishes greatly. To suggest any long term eye injury from a pointer's beam originating on the other side of a football stadium is simply not plausible.

In fact, despite the great amount of press coverage lately - and such reports resulting in the passage of laws in some places banning laser pointer sales to minors (or to anyone), there are very few if any confirmed reports of permanent vision damage attributable to these things.

We fully agree that any use of such a device in a way that annoys other people or puts them at risk - even if it is a small risk - is valid grounds for confiscation and possible severe disciplinary action.

Our own experience with laser pointers would indicate that a level of 5 milliwatts and below is unlikely to cause injury unless self-inflicted and for a substantial duration (several seconds). We say self-inflicted, as it is unlikely that another person could direct the laser accurately into someone's eye at any significant range. Almost immediately after the initial exposure to the beam, the pupil shrinks to a very small size (a few millimeters) which is an awfully small target to illuminate from a distance of even a few meters.

 

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