Laser Safety

[gandalfthegrey]

Hi All,

I've just got a new laser and it's brighter than what I'm used. A little confused about how safe audience scanning and distance is with these specs:

2.5 w RGB

Total Power: 2500mW
Power Red: 1000mW 650nm
Power Green: 500mW 532nm
Power Blue: 1000mW 445nm

DPSS is the green only. Red and blue are pure diode.

The beam divergence and scanning angles.
30,000 points /second at 15°
40,000 points /second at 8°
45,000/second at 6°

If anyone can "shed any light..." on this I'd be grateful. Thanks

[norty303]

If someone is going to do estimated calcs for you then they're going to need to know beam dimensions at aperture and divergence for each wavelength.
But really, the best way is to measure it. If you can't do the calcs or the measurements then you probably shouldn't be crowd scanning full stop is the simple answer.

To give you a really basic estimate, taking just the green on its own with typical specs of 3mm diameter and 1.5mrad divergence, and assuming no scan fail device is fitted, your NOHD is in the region of 100 metres and at 30 metres you'd be ~10 times the MPE for a 0.25 second exposure (based on the blink reflex because we're assuming no scan fail device). I'll repeat, that's JUST for the green module on its own.

Please fill out your location in your profile too, so we can see where you are and any local issues that might come into play.

[gandalfthegrey]

Thanks for the reply, maybe need to get a 500mw for smaller venues? I'm in Co. Cork, Ireland, just updated profile.

[norty303]

It would be cheaper to control the hazard in other ways, such as fitting a scanfail device and using a divergent lens like the Pangolin SafetyScan lenses (~£120 each).
Controlling the hazard by simply using lower powers is pretty ineffectual (from an effect point of view, you can barely see it) but if you decrease the power density by spreading the pwer over a wider area then you can use much higher powers safely.

But you MUST be able to evaluate whether its safe, even with a lens, so some way to measure and also to understand the calcs required is paramount.

[gandalfthegrey]

I can scan wide and keep the beams moving fast in the local venue, but it's not that big a place, especially there is not a very high roof for scanning 3 metres above peoples heads. Whats confusing me is the major differences in opinions of people I've spoken to in the industry, and also what I read about on the web. Some are VERY careful, and others with this sort of power output just seem to make sure there isn't a single still beam pointing at anyone...

[norty303]

You have obviously spoken with those who a) understand the hazards and b) those who don't, but profess to.

It is possible to know, to within reasonable limits, based on some 'back of a fag packet' calcs whether you are massively over MPE or not. In my experience, outside of this forum, virtually every laser operator (bar one, who guided me initially before I found this place) I've ever come across talks a complete load of bollocks, but uses theories and statements that seem plausible to the uninitiated, such as the one you just glanced across in you post about 'scanning fast and wide'.

And therein lies the problem - not many people, even those doing the shows, really knows if someone is doing it the 'right' way or not. So it comes down to conscience. I 'used' to think i was safe, until i actually studied the subject (via the forum, and later through training/verification) and I was shocked how wrong some of my assumptions were (albeit well intentioned).

When considering any show, and its safety, the starting point should always be 'What is the worst case scenario?' and base all of your calcs around this.
If you don't, your calcs will not be valid should that situation arise. Whether it ever would is a moot point, if it 'could' then it should be your basis for your calcs. In most cases that scenario is a stopped scanner. And that is why a [good] scanfail device is one of the best ways of raising your MPE threshold for your evaluation. But we're getting in deep now, and this could go on for pages....

If this is new info to you, then read some more fo the forum, there are a lot of threads about safety and crowd scanning. Do a search for posts by JStewart, he normally has an input into those sorts of threads, and an interesting perspective for UK/EU dwellers (and it was his tool that i used to tell you the NOHD of your green a few posts back). I've said my piece on a few too, but don't take much notice of what i say...

[gandalfthegrey]

I spoke with JStewart this morning. They should have software Ready in a few weeks that hooks directly into Beyond and will help a great deal with all this. thanks for your time and input.

[White-Light]

You can make a calculation here: http://mpe.laserextreme.nl/

That isn't the hard part. Getting within MPE is. (Note the above doesn't allow for scanner failure).

500mw, assuming 3mm diameter beam, 1.5 mrad divergence (guestimates - you need to know these exactly) and @ 10 metres to the nearest audience member (assumed figure for this calculation), is still nearly 200 mw / cm 2 or 20X MPE with no allowance for scanner failure.

Expose any employee of the venue to more than MPE and you commit a Criminal Offence under European law irrespective of whether damage is caused. Cause damage and you're facing lawsuits from your audience and other potential criminal offences.

Listen to Norty, he knows what he's talking about and audience scans safely regularly.

One of the best ways forward is a Pangolin Safety Scan lens as divergence is your friend and you can easily tame that 1W laser to be safe with the right lens.

That said, calculations aren't enough. You need real world measurements, not assumptions and that means a suitable power meter.

Best advice overall is go on James's course and make sure you buy the correct equipment for measurement as well as a suitable lens.

[Laser Wizardry]

" 15 characters"

[gandalfthegrey]

Well, that's why I'm here, don't want to hurt anyone, and see the varying advise around the place. The Laser was built in Manchester in the UK by Laser Know How (NRG) Ltd. I will be looking into getting a meter and learning more about how to measure, but after spending over 2 grand on kit already this month I just don't have any more funds for the moment. I am particularly interested in the Beyond addon Laser Visuals Ltd is developing that will help with this. James said he may have something released in the next few weeks or so. In the mean time I'm still not at all sure about safe distances etc. I also really do want to invest in a safety lens and see how it effects the show. thanks again for the input and the warning.