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Old 07-08-2010, 08:49 PM #1
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Default Class 3B Laser Displays

Hi,

I'm looking into when I'd need goggles and the various different powers of lasers and noticed various "club lighting" devices which are sold commercially and advertised as "Class 3B Laser Device" ..... 100mW and similar.

I was under the impression that anything over 5mW can be a danger (i.e. not compensated by the blink reflex) so how are clubs allowed to shine 100mW beams onto dancefloor revellers?!

I suspect I'm overlooking something here....

Thanks!

PS, as a side question, if I have OD4 goggles, does this mean I won't be able to see the beam of a 100mW red laser (or that it's visibility will be very poor?)


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Old 07-08-2010, 08:59 PM #2
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Default Re: Class 3B Laser Displays

A properly set up laser show will follow rigorous safety guidelines. For example, there is a certain distance above the audience that a laser can shine, the lasers themselves must be out of reach of the audience, no moisture in the air that can reflect the light, power densities must be kept below thresholds, etc. I don't know all the details themselves (the people in the Laser Shows section might know better), but properly set up, they should be safe.
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Old 07-08-2010, 11:12 PM #3
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Default Re: Class 3B Laser Displays

I was under the impression that anything over 5mW can be a danger (i.e. not compensated by the blink reflex) so how are clubs allowed to shine 100mW beams onto dancefloor revellers?!

end quote

Answer, in most places, it is not legal, without doing it correctly and with notification to the authorities. However, enforcement can be lax.

Simple question, what legal jurisdiction are you in? If the US, IIIB does not legally touch the audience in any way, unless you have one of the five to ten audience scanning variances rumored to still exist in the US. A variance is a de facto permit to use a entertainment laser in public, in the US.

In Europe and elsewhere, except Sweden, if you can get the light fairly randomly distributed and kept below a certain well defined cumulative exposure per unit time, your fine. In most nations, if a incident happens, the operator gets charged with Assault, sued, etc. Some nations do require inspection or certification by a third party.

The math for the distribution is not easy to explain in one post, and suffice it to say it does depend on a large number of parameters, you can't just aim and shoot without calculations and measurements, even in jurisdictions where it is legal. Many factors are involved, diameter, divergence, exposure time, pulse width, wavelength, distance to the audience, etc.

If you can keep incident energy below the threshold, there is a low chance of eye damage. However incidents have happened in Bulgaria, Russia and other places where damage to the vision of many people in a matter of seconds has occurred. Usually involving a industrial or medical laser being misused, and in one well documented case, a pointer at a rave that had safe lasers in the background.

Static, slow moving, or stopped beams are highly dangerous, however scan speed is not the main driving force behind safety. Its very much NOT a case of faster = safer.

The fact that it is not always legal, does not stop many sellers of low cost products from just drop shipping units from China. That does bend/break the rules in many places, such as the US,UK, Germany, Australia, and Sweden. Its hard to intercept a horde of small international shipments, that are often mislabeled, so people get away with things they should not. In fact most vendors these days may not even know they are selling a potential hazard.

I should mention that people who do this professionally often have sophisticated software and hardware devices known as "scanfails" as well as good measuring instrumentation, to make sure their effects are safe.

The debate over why some governments fail in enforcing the rules is a matter of another post, and has been debated to death here and elsewhere. As lasers are starting to follow Moore's law, I suspect you will see incidents and rule changes in the future. This is due to lasers getting cheaper, easier to make, and more powerful at the same time, while being sold to people who assume if its in a catalog, its safe.


If you have further technical questions, pop into PhotonLexicon and I'll show you some math and documentation. Again, its based on cumulative energy per unit exposure time. The fact of the matter is, it is never 100% safe to audience scan. Audience scanning, and all other laser safety, is based on probability and statistics, and physics. What actually happens is a scenario is set where the odds of damage occurring is low, say 1 case in 100,000 or 1 case in 1,000,000 exposures.

Steve

Last edited by LSRFAQ; 07-08-2010 at 11:31 PM.
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Old 07-08-2010, 11:47 PM #4
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Default Re: Class 3B Laser Displays

Thanks!

PS, as a side question, if I have OD4 goggles, does this mean I won't be able to see the beam of a 100mW red laser (or that it's visibility will be very poor?)[/QUOTE]


The short answer, is: It depends on what the laser is scattering off of, and distance from the scatter to your eye. Other factors pop in, such as room lighting, dark adaptation, spot size, and the wavelength of the laser. 100 mW of 633 nanometers is far brighter to the eye then 100 mW of 658 nanometers, but the potential for eye damage from a direct hit or specular reflection, all other variables being equal, is the same. It very much depends on the transmission VS wavelength curve of the goggles, too.

OD4 is a attenuation of roughly 10,000. A back of the envelope calculation is 100 mW / 10,000 = .01 mW total available for viewing, not counting scattering losses. The unaided eye in a dark room will easily see .01 mW in a .65 mm dot. Your mileage may vary.

Up close, at night, Goggles on, with dark adapted eyes, off a white surface with a low scattering angle, you might see a faint spot. Whereas in room lighting, wide scattering angle, dark surface etc, you may see nothing!

Generally if you need to see the beam, OD2 or OD3 alignment goggles are purchased, knowing there is a corresponding decrease in protection. Your never supposed to construct your experiment in such a way that you depend on goggles as your means of safety, but they are always a wise precaution.
They have hazards of their own, too.

This is all in a sticky some place...

Steve

Last edited by LSRFAQ; 07-08-2010 at 11:54 PM.
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Old 07-09-2010, 01:41 AM #5
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Default Re: Class 3B Laser Displays

Quote:
Originally Posted by LSRFAQ View Post
... If you have further technical questions, pop into PhotonLexicon and I'll show you some math and documentation. Again, its based on cumulative energy per unit exposure time. The fact of the matter is, it is never 100% safe to audience scan. Audience scanning, and all other laser safety, is based on probability and statistics, and physics. What actually happens is a scenario is set where the odds of damage occurring is low, say 1 case in 100,000 or 1 case in 1,000,000 exposures.

Steve
See you there then Steve. Any particular section for these calcs?

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