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Old 10-20-2009, 09:41 PM #1
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Default question about eye safety,laser power

I'm a costume designer,choreographer for a performance troupe.Recently we've started using stilts in our shows.My idea is to use lasers on the costumes to make them look more spectacular.Here is what I've made so far :

http://img21.imageshack.us/img21/718...5297128785.jpg
http://img35.imageshack.us/img35/631...5297128785.jpg

I've used 5mW green lasers on these costumes,and although it looks very good,I'm not satisfied...
I want to it be more brighter,more visible etc.What is the limit to the power that does not hurt the eyes.The costumes are used in night clubs full of people.While generally the beam stays above the people,sometimes it shines on them.

My question is how to avoid injuring the spectators eyes,how much power can i use on the costumes (I need info for green,red and blue wavelengths).

Can some lenses be used to widen the beam(to make it less focused,retaining the dot at the end of the beam) ? If so,where can such lenses be bought?
I have line lenses for the lasers,so that they aren't so focused.But I want to retain the dot.

Thanks in advance


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Old 10-20-2009, 09:46 PM #2
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Default Re: question about eye safety,laser power

5mW is the maximum, but it is still probably not a good idea to have a laser shining on a buncha people.
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Old 10-20-2009, 10:32 PM #3
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Default Re: question about eye safety,laser power

If you're in the US, 5mW is the legal maximum and is non-harmful. Elsewhere you can go higher, but if you are going to be using them in front of a crowd you will need to stay at or below 10mW to keep things safe. You could use lenses to defocus them for safety, and if you build your laser using information from this forum or buy complete modules from a member here it will have a focusable lens as long as it isn't green. You're not going to find many green lasers that are focusable due to the fact that they are not a good DIY laser and the focus is always set at the factory.
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Old 10-20-2009, 10:39 PM #4
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Default Re: question about eye safety,laser power

Is there a certain amount of mW per mm^2 that is safe for a defocused dot?

Say, a 50mW laser diverged to a 500mm^2 dot size, is .1mW per mm^2 safe? Do you know of a limit EF?
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Old 10-21-2009, 12:07 PM #5
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Default Re: question about eye safety,laser power

Quote:
Originally Posted by Glutton View Post
Is there a certain amount of mW per mm^2 that is safe for a defocused dot?

Say, a 50mW laser diverged to a 500mm^2 dot size, is .1mW per mm^2 safe? Do you know of a limit EF?
If you take 5mw as the upper safe limit for brief (blink reflex) exposure, then assuming a pupil diameter of 4mm and standard divergence of 1mrad, a point blank exposure to 5mw is equivalent to 50mw viewed from about 13 meters.

These limits are generally regarded as conservative. Laser shows have used significantly higher powered lasers for many years with very few injuries. The ILDA has produced an excellent paper on the subject, here: http://www.laserist.org/files/audien...rview_2pt1.pdf

I am not quite clear what you are planning, but have you thought of using a diffraction grating? A suitable grating will split a single beam into hundreds of separate beams in an array. 100mw of green through a diffraction grating should be safe (as long as you have some method of ensuring that the beam only shines through the grating) and would be both spectacular and cheap.

David
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Old 10-21-2009, 05:09 PM #6
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Default Re: question about eye safety,laser power

5 mW entering the eye would equate to someting about 25 mW/cm2 for the worst case scenario. This level is generally considered safe (in the sense that no permanent damage is done) if the subject has a normal blink reflex. It would probably still be a pretty unpleasant experience however.
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Old 10-21-2009, 05:30 PM #7
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Default Re: question about eye safety,laser power

I'd suggest using smoke/haze, or dimming the lights and/or blacking out the room for a more spectacular effect.
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Old 10-21-2009, 05:58 PM #8
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Default Re: question about eye safety,laser power

Those are the easiest steps to get beams visible... but once you've exhausted those, more power is pretty much the only way to go even brighter. Working with wider beams so you can use more power without increasing the danger is a good idea then - at least in situations where you cannot avoid potentially exposing the audience.
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Old 10-22-2009, 01:39 AM #9
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Default Re: question about eye safety,laser power

Quote:
Originally Posted by ElektroFreak View Post
If you're in the US, 5mW is the legal maximum and is non-harmful. Elsewhere you can go higher, but if you are going to be using them in front of a crowd you will need to stay at or below 10mW to keep things safe. You could use lenses to defocus them for safety, and if you build your laser using information from this forum or buy complete modules from a member here it will have a focusable lens as long as it isn't green. You're not going to find many green lasers that are focusable due to the fact that they are not a good DIY laser and the focus is always set at the factory.
So a 10mW laser with defocusing lens should be safe ? And where can one buy such a lens ?

Quote:
Originally Posted by davidgdg View Post
If you take 5mw as the upper safe limit for brief (blink reflex) exposure, then assuming a pupil diameter of 4mm and standard divergence of 1mrad, a point blank exposure to 5mw is equivalent to 50mw viewed from about 13 meters.

These limits are generally regarded as conservative. Laser shows have used significantly higher powered lasers for many years with very few injuries. The ILDA has produced an excellent paper on the subject, here: http://www.laserist.org/files/audien...rview_2pt1.pdf

I am not quite clear what you are planning, but have you thought of using a diffraction grating? A suitable grating will split a single beam into hundreds of separate beams in an array. 100mw of green through a diffraction grating should be safe (as long as you have some method of ensuring that the beam only shines through the grating) and would be both spectacular and cheap.

David
The 100mW + diffraction grating also sounds good.Is there a minimum distance between the grating and the laser source,or can I put the two almost in front of each other ?
And again,where can such a grating be bought ?
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Old 10-22-2009, 10:28 PM #10
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Default Re: question about eye safety,laser power

Since lasers typically have low divergence, the distance to such grating would not be critical. The distance between grating and anyone watching it would.

In any case, adhering to 25 mw/cm2 would be a good idea, unless you can completely ensure some other mechanism (such as scanning with a failsafe beamstopper) would ensure operation within safe limits.
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