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Hi Carl,
I personally wouldn't use an undiverged 150mW laser in close proximity to the laser. And yes, 27 meters is a bit too close... The answer is... divergence. As the beam gets bigger, it becomes safer at a square-law. Double the beam size and make it four times as safe. The idea is that less and less of the beam can get into a fixed pupil diameter of your eye. Probalby not said very well, but I hope you understand what I mean.
Bill
Also it is hard to rely upon fog as a factor, just because of how unpredictable it can be. Also some wavelengths will propagate through fog/haze/pollution better than others. Hence the reason why sunsets are red and the sky is blue.
Regarding what Bill mentioned you might want to check out this link:
http://en.wikipedia.org/wiki/Inverse-square_law
I perplexed my high school physics teacher when he was talking about the inverse square law - I asked him if lasers follow the law. I figured they did since it is a 'physics law' but he stopped dead in his tracks - but I love physics because of that class :D
EDIT: This post just hit the 4 figure mark for me :P
:) Not at all, I was just worried that I had either missed something in the legislation or misinterpreted something and got it completely wrong! <breathes a sigh of relief>Quote:
Originally Posted by Lynx
Cheers
Jem
There is a meeting of laser safety professionals called the International Laser Safety Conference, or ILSC. There is no set schedule for ILSC -- basically, they hold a meeting any time they have collected enough interesting papers, or when things change significantly. However, the ILSC has been happening about once every two years in recent days.Quote:
Originally Posted by mliptack
At one of these ILSC, we were discussing this, and in one of the paper presentations, they presented both the measured data and theoretical results. Of course, theoretically, lasers should follow the inverse-square law, but in this paper, the data showed that lasers only roughly followed them. The measured data was a bit different.
In the meeting Jerome Dennis (recently retired from CDRH and certainly a big wig in the field of Laser Safety) stood up, and said that the inverse-square law wasn't a law at all, but a recommended code of practice. Of course everybody laughed... (If you are at least not grinning right now, then I guess this is either a timed-release joke, or something where you had to be there, to get...)
But it does show one important point, and I started to make this when I wrote my post above, but then stopped because I couldn't find the right words.
The point is -- theoretical results are *something*. They get you *somewhere*, but ultimately you need measurements to confirm your expectations, and ultimately, when it comes to public safety, you need to perform measurements to make sure the show does not exceed the MPE.
When we do audience scanning here in the US, we use a combination of a specialized light meter, and a fast photodetector with 7mm aperture, and before each show, we do a measurement to make sure that the laser will be safe for the audience. This measurement is to be done each night -- basically before each show. And as part of a CDRH variance, that variance is granted based on our agreement that we will follow a step-by-step procedure, and make measurements. Measurements are the only way to know for sure what's going on. There are a lot of variables that might influence the measured-versus-theoretical result. For example, beam quality, beam size (often time they are different for red, green, and blue), and other factors might make the laser not appear to follow the inverse-square law.
James posted some information above about software he has which will help people to assess audience scanning. That software will present some results that are *something*, and will get you *somewhere*, but still, before you actually do audience scanning in a public venue, there will be absolutely no substitute for real measurements.
I do applaud this kind of software because, for people who have never done audience scanning before, the software will show exactly what you need to do in order for it to be safe. For example, the software should clearly show that, either you have to increase the divergence in the audience, or turn down the power, period. There really aren't too many degrees of freedom here... But a lot of people don't know this and, as I wrote above, increased divergence might seem like blasphemy... But without the software (or experience and measurement equipment), the assumption might be that, given the right scanners, right scan-fail board, and right imagery, you can make a safe show. Well, no. Not really... Scan speed has a relatively small impact on safety (a 10X increase in scanning speed only buys you around a 2X increase in safety), and the implication is that beam velocity changes within imagery itself -- i.e. the imagery -- really doesn't have much of an influence on safety. The greatest influence comes from beam power and beam divergence, with the single biggest contributor being divergence.
In any event, for people who are just speculating about doing audience scanning, low-cost software would show what they need to do to their projector in order to do it safely. Low-cost software might certainly be less costly than the measurement equipment and training, so this is certainly useful. But in the end, before a public presentation, there is absolutely no substitute for measurement equipment itself. So maybe the software will educational and inspirational to some -- to spend the money and get the measurement equipment, and for others it might be convincing enough that it's just not worth the additional equipment investment to do it right...
Best regards,
William Benner
This is a great thread :)
How about some more information as to what's actually available as regards safety systems? Why is it so difficult to find out what's out there, is it some sort of big secret?
Bill, What exactly IS your system for diverging the beams and how much does it cost?
James, Likewise a good explanation of your scanware hardware/software system would be good, along with some approximate costs.
Perhaps someone could add some info on exactly what is required to enable us hobbyists to make our projectors fully 'safe' for audience scanning. Even if we can't afford it at least we'll be fully informed and it will give us something to aspire to.
What really hacks me off is that I am a concientious person and I *REALLY* want to do things right, yet there are countless mobile DJ's who are audience scanning in the UK without even giving it a second thought.
I haven't done any audience scanning so far as i'm not fully conversant, nor comfortable with working out the MPE's for all the different effects that can be produced in LivePRO. Perhaps that's because I work in Optics and have a conscience, it wouldn't look good if I screwed someone's vision up.
Having said that, i've also tried to do some research into injuries caused by lasers in entertainment, so far i've drawn a complete blank. O.K., so perhaps they are not reported, but you would think that with all the mobile DJ's, who point raw undiverged beams straight into the audience, and are using cheap chinese lasers with no IR protection there would at least have been one or two significant injuries. That's doesn't mean i'm saying that there is no risk!, just that there are no reported injuries.
So come on guys, spill the beans, tell us what your systems are and what they cost. Tell us hobbyists how we can make our projectors safe for audience scanning... Education is a wonderful thing and I for one am listening :)
Cheers
Jem
Hi,
Nice discussion here.
I understand that some companies try to promote their high professional systems here, but the question was about a scan fail detection system, not a system to make shows "safe".
A scan fail detection does not make a show safe. But it is a part of the system, which makes it more easy to get the permission to install your system and make your show (country-dependant).
For example, our 'Raytrack' series of scanners, using DT40 galvos, are all supplied with a simple on-board scan fail detection.
Naturally... ;-)Quote:
Originally Posted by Pangolin
Our system is microcotroller-based, but it works great. You can always make things 'better' or more complicate or more expensive. This is progress. I designed the first kind of this safety ('safeguard' from Medialas) 1997. At a time, nobody cared about such a thing. And until now, we never had any 'safety-problems' with it. It is a simple and practical way to avoid safety problems, caused by scanner failure or programmed static beams.
On the other side, you can try to make your show absolutely safe by spending thousands of $ in products, nobody has seen in practical use until now. And nobody ever has seen the result of a safe show, using such a system (except maybe the developer).
There are many systems in Europe which are approved by the 'TUV' (safety organization), just BECAUSE our existing small thing is part of the system. It is quite funny, that most of our customers first do not recognize this small board on the scannerdriver. They just see the price of the complete scanner, which natuarlly is about $100 higher than a scanset without such an add-on. But when they want to install their system in the public, they ask for a scan failure detection. Then they pay at least double the cost for such a system + mounting and connecting it to an exisiting lowcost scanner (which does not have any access points for signals in many cases).
www.laser-safety.deQuote:
Originally Posted by Carl B
www.medialas.de
www.mylaserpage.de
Our scan failure detection is only designed for the use together with our Raytrack scanners http://www.jmlaser.com/products_engl..._kurzinfo.html
Normally, the modulation signals of DPSS lasers are shut down via optocoupler.Quote:
Originally Posted by Carl B
Some systems use a shutter, but these parts are very slow.
Testing is simple: Just point a single point with your software and check if the laser is blanked. Alternatively, you can scan a pattern and zoom down the size via software, until the laser is blanked. Or you scan a pattern and slow down scanspeed until the laser is blanked.
Joachim
Hi Jem
I totally agree there seems to be little or no real information regarding how to provide a fully safe audience scanning system.
There is some very detailed information available from Pangolin, Greg (LSDI) and the master document from John O' Hagen HPA the full thesis is available on the Pangolin web site.
The nearest most appealing solution seems to be the PASS system, I have no direct experience with this product, but from what I have read it does cover most of the concerns relating to audience scanning safety. Using beam power monitoring, very fast shutter (PCAOM), power supply monitoring, analog circuits with multiple redundancy.
Using any processor based safety system will need multi processors running different software algorithms that can be checked by safety specialists to determine if all WHAT IF's have been taken into account.
Laser Visuals product does have the possibility of providing additional micros, but does it have exactly the same firmware in each additional micro ??
As I had mentioned in my previous post no one person can fully assess the risks. Maybe James has passed his product onto John O' Hagen or John Tyrer for their independent assessment, if so it would be very interesting to here their views regarding this.
I remember a conversation with John O' Hagen regarding LV scan safe software calculator, he seemed to think like myself that if you feed the incorrect values into the software the result will be correct based on the input. If you do not fully understand the physics then you are unable to assess the risks fully.
I feel that a one day course on laser safety is not adequate, especially if you don't understand the calculations or the procedure to assess the risks. I am only aware of one course in the UK that will cover all aspects of laser safety, HPA(Health Protection Agency) with Loughborough University, a full week of intensive training including workshops, practical measurements, peer assessments, final exam and John O' Hagen and John Tyrer as course tutors. I am not aware that even James Stewart has attended this course ???, but if he has he should know that the beam risks are a small part of laser safety.
I have discussed the problem of DJ's scanning the audience without risk assessments, scan fail etc. with John Tyrer and HSE personnel and would personally like to see a license system introduced into the UK to ensure that if you are to use class 3B class 4 lasers you need to prove have been trained correctly by a recognized institution.
As regarding injures the reason that we do not find any real evidence of eye damage from laser displays is that if you do not take a direct hit on your retina with a power high enough to cause blindness, the chances are you will have received damage somewhere with the eye, but your brain corrects this damage and there are very few nerves to generate pain to indicate small but significant damage. We are all aware of damage to CCD digital cameras, video projectors and even paper & balloons. The evidence is not easy to find as most damage can only be found after a full eye examination buy someone who is looking for laser damage !!!
It is very clear that you cannot expose anyone to an unacceptable risk, but laser safety is very complex and does cause major debate amongst safety professionals.
I think that the easiest way is not to scan the audience with any laser unless you fully understand what you are doing, even then your assessment will need checking from somebody else who has the same understanding. I work very closely with John Whymark (WOW! multimedia Ltd. ) who does fully check my assessments and always he will see things that i have missed. He is a mechanical engineer with experience in industry as a safety officer and consultant to assess equipment for CE approval.
This then brings me to an interesting subject. If you were to retrofit a scan fail system into your projector you will need to re-assess the unit for CE approval (if the projector has been approved in the first place !!!!) therefore home made projectors without CE approval are illegal to use in any public place. PUT THE CAT AMONGST THE PIGEONS HERE !!!!???? So hands up how many of you guys have CE approval ??
The best current document to help any one considering audience scanning is the latest IEC/TR 60825-3/Ed.2 This is a guidance NOT LAW but it is the yardstick that would be produced in court if you ended up there !!
If James from LV has helped venues obtain local authority approval for audience scanning maybe he could publish a draft example in order to help us all understand the mechanics of how to approach such a subject, this should be in his own interest as well as helping us all understand. I have not ever been able to produce a convincing risk assessment for audience scanning that would even pass John Whymark's close scrutiny never mind John O' Hagen.
Maybe it is possible to convince the local authorities that an adequate risk assessment is ok due to the fact that they have no real experience in laser safety or they all seem to use the HSG95 (USELESS). Many still quote Class 3A lasers ??? this information is also available from the HSE as a guidance to local authorities.
I am hoping to attend the annual laser safety forum this year to discuss these issues with John Tyler and John O' Hagan, maybe we may see some action regarding the safe use of lasers in the UK.
Regards
Kevin
Jem;Quote:
Originally Posted by Jem
I remember this being discussed in another audience scanning thread a while back - not sure if you saw that thread or not. But anyway, the Pangolin system has a *huge* honkin' lens mounted on the projector that causes the beam to diverge. I've actually held one of these lenses in my hand, and let me tell you - it's massive! Weighs about 5 pounds I would guess, and it's about the size of your average computer mouse. (But round, of course!) I'm betting that you could drive a car over the thing and not break it.
These lenses cost somewhere around $1200, if I'm not mistaken. And a lot of that cost is tied up in the grinding process of the lens itself. Plus they have to pay a license fee to AVI for each one.
I don't think it's really practical for a hobbyist's projector, but if you're doing commercial shows and you want to crowd scan, it's one very important piece of the whole safety package that Pangolin sells.
"Aspire to" is an apt term. In my opinion, audience scanning is something that is currently out of my reach. For sure I don't have the equipment to perform the power measurements correctly, nor do I have a good understanding of the calculations involved. I can't really afford the diverging lense needed, and finally, I don't have a scanner safety system in my projector. I think a lot of the hobbyists here on PL fall into this same category.:(Quote:
Perhaps someone could add some info on exactly what is required to enable us hobbyists to make our projectors fully 'safe' for audience scanning. Even if we can't afford it at least we'll be fully informed and it will give us something to aspire to.
I hear you there. It does make you mad when you see people being careless. Some people take that as encouragement that audience scanning is not that risky. But like Kevin mentioned above, laser eye damage is difficult to detect. That's probably why we don't see more cases of laser-induced eye injury.Quote:
What really hacks me off is that I am a concientious person and I *REALLY* want to do things right, yet there are countless mobile DJ's who are audience scanning in the UK without even giving it a second thought.
Still, like you, I feel that the lack of reported cases isn't enough to convince me that the practice of audience scanning (without the proper safeguards) is a good idea.
I'll admit that I'm curious as to how high the price tag will be. But I expect it will be *way* out of the range of your average hobbyist.Quote:
Tell us hobbyists how we can make our projectors safe for audience scanning...
Adam
Good, then let's have as much information as possible. Everybody please feel free to chime in :DQuote:
Originally Posted by Lynx
Yea... Tried reading that. It's great for insomnia ;)Quote:
and the master document from John O' Hagen HPA the full thesis is available on the Pangolin web site.
I suspect that there are *VERY* few people who *FULLY* understand the physicsQuote:
If you do not fully understand the physics then you are unable to assess the risks fully.
Probably a slight misunderstanding here... I think the problem I have to come to terms with is evaluating a *WHOLE* laser show when using LivePRO. As I understand it you should assess *EVERY* effect that will be used in the show to ensure it's safe. That adds up to one huge pain in the ass. I think i've probably taken the best decision just not to do audience scanning at all :)Quote:
I feel that a one day course on laser safety is not adequate, especially if you don't understand the calculations or the procedure to assess the risks. I
Agreed, but only relevant if you are wanting to specifically do audience scanning ;)Quote:
I have discussed the problem of DJ's scanning the audience without risk assessments, scan fail etc. with John Tyrer and HSE personnel and would personally like to see a license system introduced into the UK to ensure that if you are to use class 3B class 4 lasers you need to prove have been trained correctly by a recognized institution.
I work in Optics - Remember? ;)Quote:
As regarding injures the reason that we do not find any real evidence of eye damage from laser displays is that if you do not take a direct hit on your retina with a power high enough to cause blindness, the chances are you will have received damage somewhere with the eye, but your brain corrects this damage and there are very few nerves to generate pain to indicate small but significant damage. We are all aware of damage to CCD digital cameras, video projectors and even paper & balloons. The evidence is not easy to find as most damage can only be found after a full eye examination buy someone who is looking for laser damage !!!
All our Optometrists know I have an interest in this subject and they have been asked if they will 'keep their eyes open' (:D) and look out for possible signs of laser damage. I also know many other Optometrists who are all on the lookout for any potential signs of damage. We alone see many hundreds of patients per week within our company, so I guess the law of averages says one must show up eventually !
I think (as in the optics business) some people are serial worriers and want to protect their jobs. These are quite often the people who have most to gain by setting up a 'closed shop'. Everything has to be carefully balanced and the risks assessed otherwise we'll just see another raft of legislation that has no meaning in real life.Quote:
It is very clear that you cannot expose anyone to an unacceptable risk, but laser safety is very complex and does cause major debate amongst safety professionals.
That's why I don't do it ;) Although I do sometimes wonder if i'm too over cautious. It just worries me that if I were to assess each individual effect that I was to use i'd spend all night doing the assessments and not have time for doing the show!Quote:
I think that the easiest way is not to scan the audience with any laser unless you fully understand what you are doing
Not even going to go there :D... But.... If I were you i'd put my hard hat on and duck down behind the sofa straight away ;)Quote:
This then brings me to an interesting subject. If you were to retrofit a scan fail system into your projector you will need to re-assess the unit for CE approval (if the projector has been approved in the first place !!!!) therefore home made projectors without CE approval are illegal to use in any public place. PUT THE CAT AMONGST THE PIGEONS HERE !!!!???? So hands up how many of you guys have CE approval ??
I'll take a look at that, thanks. I think this is the document that James was going to summarise and send out an 'update' to all who had been on the LV safety course.Quote:
The best current document to help any one considering audience scanning is the latest IEC/TR 60825-3/Ed.2 This is a guidance NOT LAW but it is the yardstick that would be produced in court if you ended up there !!
I take it that you don't do audience scanning either then... or are you doing them without fully assessing the risks ;) :DQuote:
I have not ever been able to produce a convincing risk assessment for audience scanning that would even pass John Whymark's close scrutiny never mind John O' Hagen.
Hmmm... That action needs carefully watching to ensure it's carefully balanced. As I said before, those with vested interests can manipulate legislation in their favour - i've seen it happen in other industries and it benefits no-one in the long run.Quote:
Maybe it is possible to convince the local authorities that an adequate risk assessment is ok due to the fact that they have no real experience in laser safety or they all seem to use the HSG95 (USELESS). Many still quote Class 3A lasers ??? this information is also available from the HSE as a guidance to local authorities.
I am hoping to attend the annual laser safety forum this year to discuss these issues with John Tyler and John O' Hagan, maybe we may see some action regarding the safe use of lasers in the UK.
All interesting stuff though.
Cheers
Jem
CE marking only applies to 'production' equipment. Home-built rigs are effectively prototypes, which aren't covered by any legislation. Many people in the UK have been running safe laser shows for decades using homebuilt equipment. Suggesting that the use of such equipment is illegal is just disseminating inaccurate information.Quote:
home made projectors without CE approval are illegal to use in any public place.
The safety board made by HB Laser is a little difficult to find on their website, so here's a link http://hb-laser.com/hb-en-apolloscanner.html
The biggest contribution to safe audience scanning, however, is in good figure design, so that the beam is kept moving at a constant speed - for example, draw a triangle as 3 lines and 3 loops, thus avoiding the 3 'hot spots' at the apexes. Such an approach also makes exposure measurement much easier, as brightness will be constant for all of the figure.