New Laser MPE Limits published

For anyone interested in laser MPE, I’ve posted some details up on our website regarding the newly published exposure limits.

http://www.lvroptical.com/blog_MPE_limits.htm

The new limits will appear in the next editions of the IEC and ANSI laser standards, (which are in a very advanced stage of development), as will be the case with worker exposure limits published in the Artificial Optical Radiation Directive in Europe.

Until then, keep with the existing limits. But as a heads up, newer limits are on the way!

James

Hi James,

In terms of mw cm2 what effect do the new limits have?

The MPE for a 0.25s accidental exposure is 2.5mW/cm^2 , which is the same as 25W/m^2

This side of the pond, which includes IEC and ICNIRP, we express the area in m instead of cm, but both are the same. There is just a multiplication or division factor of 10,000 if you want to go from one to the other.

The limits published by ICNIRP are international, so these end up being used worldwide in safety standards and legislation etc.

So the increases and decreases I summarise in the text are equally valid for whatever your units of choice are.

James

Just been looking again as I misread it 1st time around. Has it actually changed the MPE limit when using the simple method?

Thanks James.

Interesting reading, thanks. Should not change lots since most of us already used the single pulse method anyway...

By the way, which component should I use to measure the pulse length of scanned effect? A fast silicon photosensor should do the job, but I'm not sure how fast should it be. I found one with rising/falling time in the 10th nanoseconds, but propagation delay is still 5 us?! Is it fast enough to have a sub-microsecond resolution on the scope?

Is it not the case that even if you have a single pulse in the us range, your exposure timeframe should still be based on the lowest of your scanfail response time (typically 1 to 20ms) or blink reflex (250ms)?
Otherwise you are still waaaay in excess of MPE in the event of a fault condition.
i.e. nothing will really change with regard to how we currently crowd scan.

Or am I missing something significant here James?

Hi James
Give me a call, to discuss this.
Could you tell me where the HSG 95/PM 19, data was implemented, and sanctioned.

The main point of me posting this news and putting a little piece about it up on our website is that, rather than people hearing rumours of changes, getting excited or dismayed etc., I could spell it out from the outset. And also give people a bit of an insight as to where/how the limits are agreed, and also how they then end up being used as the exposure limits in safety standards/permitted workplace exposures etc.

Not sure I understand your question Clive. HS(G)95 and its predecessor PM19 always referred to ICNIRP data. Nothing has changed with the current version of HS(G)95.

As you know HS(G)95 is shortly to be reviewed by a group that PLASA has gathered together. If it’s decided to keep exposure limit references in the document, I’m sure they will end up being the limits that are mandated through the AORD and published in the most recent IEC laser safety standards. i.e. by the time a revised HS(G)95 is agreed, the 2013 ICNIRP laser exposure limits will be the accepted norm.

Adam, you are right in that the effectiveness of your scan-fail monitor/termination system is usually the most limiting factor in an assessment. The new way that Cp is considered supports the argument for being able to consider single pulses, especially at the shorter durations, when there is an increased chance of more pulses occurring; then of course the average MPE could still come into play if the pulses occur too frequently.

You are right though, nothing will really change with how people crowd scan – most people that do it will do so without even attempting to get anywhere near the exposure limits! – ignoring the need the alter the irradiance of the beam, or having a decent scanner health monitor in place. :(

Something like a Thorlabs PDA100A/DET100A type detector is a convenient little package that has the silicon diode and amplifier self-contained and can be hooked up to a scope to see the pulses. A DSO with a bandwidth of several MHz will keep you from having nyquist issues.

James

James
The current implemented HSG guidelines for laser displays within the UK are HSG95, and as such exposure levels or safe practice hasn't been proven or disassociated.
I was hoping you might call me regarding this.
Let me throw a new concept in the discussion, We have multiple suppliers of lasers that are being used, that have no inbuilt safety, Ir or Uv filtering.
People harvest components and make them freely available, building a light source without the ramifications of what they sell or hire, having no implementation of the original design, leaving people exposed to serious levels of radiation.
Would it not be prudent to ask Casio or one of the other commercial suppliers to get involved on the revision of the crowd scanning debate.
Casio produce a laser based video projector that people harvest components from, Mitsubishi, Coherent are also providers of such components.
Let's get some big boys on board and the HSE.

Quote:

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Originally Posted by Laser Electronics Ltd

James
The current implemented HSG guidelines for laser displays within the UK are HSG95, and as such exposure levels or safe practice hasn't been proven or disassociated.
I was hoping you might call me regarding this.
Let me throw a new concept in the discussion, We have multiple suppliers of lasers that are being used, that have no inbuilt safety, Ir or Uv filtering.
People harvest components and make them freely available, building a light source without the ramifications of what they sell or hire, having no implementation of the original design, leaving people exposed to serious levels of radiation.
Would it not be prudent to ask Casio or one of the other commercial suppliers to get involved on the revision of the crowd scanning debate.
Casio produce a laser based video projector that people harvest components from, Mitsubishi, Coherent are also providers of such components.
Let's get some big boys on board and the HSE.

---

Where exactly is this going? This talk of 'the big boys' bothers me. Is this really about safety? Or is it the beginnings of an attempt to stitch up the budding industry for the well-established few to deprive fun and possible earnings for many?

Those are deliberately loaded and provocative words to make the point, but this is actually an innocent question. I really don't know what you're implying. I hope it is based strictly on safety. Because if it isn't it is very similar to the half-baked attempt to legislate to prevent legal highs. While that fantasy about 'cream supplies' when it's obvious to all who know, that the meaning is laughing gas, is a thing I find disgusting, as I think it better to say it like it is and not hide what is basically drug-dealing in a cloak of 'barely legal' convenience, if the 'big boys' close it like a cartel, it is very likely that similar venal deceits will be put into the public domain in order to sell various laser parts to what is in many ways a related market! The desire to share a collective and fun experience. In many cases the venues are literally the same. Raves. My outlandish metaphors are soundly based in a real condition.

In all cases where a limited few have mounted what is effectively a protection racket, the danger is driven underground where it usually thrives. In the case of lasers that might be harder to do but only because they are so intensely visible! :)

When I read the HSE guidelines I remember something I liked. Was a long time ago now, I don;t do shows so it's not something I keep close tabs on, so my memory is vague..Anyway, there was a description that showed you could make sensible estimates of safe limits based on CW power, scan speed, distance from scanner, dwell time, etc, and that so long as you made an honest attempt to stay on the safe side of a limit you were likely ok. If the estimation were vague, you'd end up being that much further away on the safe side so long as you made an honest effort to judge it well. Once you end up demanding expensive metering and expensive fast digital storage oscilloscopes you get specsmanship, people edging for stronger power than in other shows, people competing to push the envelope. By demanding what appears to be more rigor there is a risk of people getting closer to real danger while believing that their expensive instrumentation will protect them from both lasers and the law.

It's a lot easier to plot a course that cannot produce a dangerous pulse to an eye than it is to measure one if you're trying for all the 'safe' power you can get within the law. The more people try the harder that will get.

Now that was a vague and overlong post, but I think it makes the point well enough: More people are getting into this. So make it possible for them to be safe with the limits they have, and don't risk forcing them to hide from you when experimenting with weird and risky toys. To do anything else is effectively making things more limited and riskier under the guise of making things more safe. It sounds to me like the big boys in the show industry getting scared that legislation might kill their joy because of all the reckless newbs butting in. But you can't put the genie back, you can't watch in every dark hall where it strays over the ropes, and the best thing you can do is keep things as simple as possible, measurable with the cheapest and most widely available means as possible, so that the newbs will be able to correct each other. That way you won't have to worry so much yourself.

In the last post here I spelled out a problem, so I might as well have a shot at a solution too...

Expensive metering turns a scientist into a priest if it's so costly that only what amounts to a priesthood can afford it, but there is a neat way to avoid that risk. Make some tiny widgets with a fast photodiode, a differentiator built with the same low-loss parts you might use for a UHF tuner. Calibrate them with that expensive gear so that they drive a comparator that beeps through a piezo disk and flashes an LED if a light pulse hits it capable of exceeding MPE. Do it in serious bulk. That way the cost will be dirt cheap per unit, and several people will likely have one in any venue with a laser in it. It should be possible to make a simple unit cover a wide variation of power and duration for a given energy reading. The power of a firm like Casio might be well advised to make them anyway, just to let people feel safer about havign these new high power light sources in their homes.

Clive,

HSE’s HS(G)95 guidance for laser show applications have underpinned what venues, show providers, and (knowledgeable) local authorities expect to see as acceptable laser safety management, since its publication in the mid nineties. In 2010 government legislation mandated the laser exposure limits, through implementing its obligations as an EC member state in relation to the Artificial Optical Radiation Directive. The law that was passed through parliament now sets the legally binding limits through regulation. HS(G)95 in that regard takes a back step, as the regulations that enact law take priority over any guidance.

The reason the HS(G)95 is up for review is that it’s a little dated with the law having moved on since its introduction. In days gone by, HSE would have updated the document themselves. But with a political drive to ‘appear to be seen’ as government reducing the grip it has on business, with H&S, (and the need to cut costs!), when this document came up for review, it was seen as good candidate to be reviewed, maintained, and published by industry. Which is what is starting to happen with PLASA’s panel having been assembled.

The important thing to remember is that HS(G)95 is not a ‘crowd scanning debate’ document. It is supposed to give a broad overview to laser safety management for laser show applications; ‘crowd scanning’ is only one small part the range of issues that need to be considered on a display installation.

I haven’t come across any issues with UV or IR being a greater problem than the primary concern of visible radiation exposure from laser projectors?

I don’t really understand why Casio would want anything to do with discussing ‘crowd scanning’ issues or want to get involved with a laser show safety management guidance document, when for their normal intended use, Casio products do not expose persons to light that would be considered a laser product.

I appreciate that there is an ongoing disagreement between some show providers and what the scientists have agreed are the appropriate exposure limits. But that aside, I’m not sure that even if the existing limits were relaxed, even by a 100 or 500x, if it would change the behaviour of many laser show users that make absolutely no attempt to quantify what they are putting into the faces of others.

James

Jeeze,

Where do I begin, Fast photodiodes and UHF tuners? Do you even own scanners and software?
That is non-sensible and shows no grasp of the physics problem.

The reason is not the "Big Boys", the reason for the UKs Functioning laser safety system is well, safety... HSE may be overkill, but at least they get the local and regional folks to inspect. Unlike here in the states.

I know some of the people who set up a great part of the UK system rules, and they were NOT profit motivated fools. In fact they were
a mix of academics and industry types. The one I know the most, wrote his Doctoral thesis on the problem. He went out to clubs, made measurements, and made his peer reviewed results available to the public. He showed up at ILDA conferences and asked for his work to be challenged, some of it was challenged. This is not rocket science, its a well documented issue. The papers are on-line to be read.

Here is a the deal, the difference between a good exposure and a bad exposure is the initial laser power, divergence, pulse width, and distance to the audience. Exposures are cumulative. So a bad wavelength calibration on a PD is not a real issue. The real issue is a accurate measurement of the laser's CW power, a good ballpark measurement of the divergence and pulse width. Then tracking the cumulative number of exposures. The PD is solely used for pulse width, not power.

A 100$ PD is almost overkill, in fact. Its calibration vs wavelength does not really matter, in fact, as long as its not saturated during the measurement, and properly terminated at the scope, it really does not matter much unless its blind at the wavelength in use.


But guess what, a standard LPM with a 5% error is not that bad. A decent photodiode is less 100$. A decent used oscilloscope is 100$ on Ebay, or 300$-450$ for a New Chinese scope fast and accurate enough to solve the problem. If you can't afford that, you probably should not be exposing eyeballs in a public environment. An accurate enough divergence measurement can be done with a 20$ Ebay digital micrometer, a piece of paper, and a tape measure.

The LPM needs some measure of traceability and needs to be commercial product. But even a used one is usually close enough on calibration. Of the five I've bought, most were within 5% even after a decade of use. Its easy enough to bounce test a used one off a new one or recently calibrated one. There are decent laser power meters all over the globe.

Lasers drift in power, so the other thing is doing the measurements pre-show, and not assuming it performs the same, event after event.



The Industry, has a moral duty to not go Cheap on safety. You, "Doctor", have a moral duty to look at the math and physics before you go spouting off about the problem's solution and the state of an industry you do not even participate in.

Steve Roberts

So find a way to get that calibrated measure cheaply into the hands of many people. Whether I know the physics or not is irrelevant. You're going to have to get some gadget into the hands of thousands of people who don't. Instead of berating me, fix that problem, if you know how.

Is there really no type of photodiode that puts out a signal proportional to power received at those speeds?

(My post was late last thing yesterday. Probably shouldn't have been... The 'UHF' comment was based on one thing alone, an assumption of handling pulses about a nanosecond in duration. Basic electronics suggests that standard low-loss parts for UHF, i.e. 800 MHz or more, would be needed to handle the small signals. My point being that there are lots of those from the TV industry so they will be cheap.)

Quote:

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Originally Posted by Laser Electronics Ltd

James
The current implemented HSG guidelines for laser displays within the UK are HSG95, and as such exposure levels or safe practice hasn't been proven or disassociated.

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The levels are based on more than 30 years of research and statistical data regarding eye injuries across the world.

That said, the levels are now known to be conservative and there's a lot of support for the approach to audeince scanning suggested in Greg Markov's paper which involves a proposed level of 10x the current MPE.

Quote:

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Originally Posted by Laser Electronics Ltd

Would it not be prudent to ask Casio or one of the other commercial suppliers to get involved on the revision of the crowd scanning debate.
Casio produce a laser based video projector that people harvest components from, Mitsubishi, Coherent are also providers of such components.
Let's get some big boys on board and the HSE.

---

Personally I'd rather see this responsibility handed over to ILDA.

With most of the World's laser experts at its disposal - people such as Markov, Benner, Murphy, O'Hagan surely there's no organisation better qualified to set the level than the ILDA board.

OK, how I am I going to make this point to you? The MPE meter is but a somewhat useful toy. If you can't do the math, which is simple. le, you wont get the gig past a safety case in the US or UK


Here is your homework:

Two amusement parks are on opposite sides of a lake. The lake is 1.234 Kilometers wide. A 25 watt argon laser based show is ran by a bunch of 19 to 24 year old boys. The laser has a divergence of 1.65 milli-radian and a initial beam diameter of .80 mm.

Every night a 19 year old Buxom Blond who is majoring in Dance Theatre takes the stage at the other amusement park. She's really hot... The boys at the laser show use binoculars to watch the stage show across the lake. Amusement park B cannot afford lasers, so when they get to the 60's music part of the stage show, a bunch of fans blow the girls skirt up, like Marilyn Monroe in the famous picture. The boys at park A decide the cheap PAR can lighting is unworthy of lovely Marilyn, and illuminate her back side with the argon to boost her already heavenly glow.


Show your math and equations:

Part one

"Marilyn" turns around during the illumination. She's not wearing glasses, so assume 7 mm pupils, fully open. Is she Eyesafe?
What is the class of exposure at her face?

Part two:

Marilyn performs on a tower on a barge. US NFPA 115 code specifies 0.5 watts cm^2 visible light as the point at which a show laser constitutes a possible fire hazard. If Marilyn is wearing black tap pants under the white dress, how close to the laser booth does the barge have to drift before Marilyn wonders what is burning?

Part three:

Marilyn steps off the fake 20 foot oil derrick she performs on, so the boys aim the beam 25 degrees up in the air. What is the Nominal Ocular Hazard distance from the beam, assuming the laser is emitting 100% 514 nm light? What is the Critical Zone Exposure Distance assuming the laser is 100% 488 nm?

Part 4

After holding Marilyn when she nearly fell off the tower, her boyfriend the stage lighting guy at park B decides he needs a laser in the indoor show. He purchases a 70 mW ILT krypton with 4.5 milli-radian divergence and a initial beam diameter of 2 mm from Ebay. The laser is performing perfectly and the specs given are exact. He can't afford a galvo pair, so he aims the beam at a tilted mirror on a motor shaft. The cone described is 15 degrees full angle and the motor is spinning at 250 RPM. To a first approximation, what is the static beam diameter at 75 feet where the audience is? If the eye is 7 mm across, what is the approximate pulse duration at the eye assuming the beam is a true square wave with straight edges and not Gaussian. The motor slows down to 10 RPM, what is the pulse duration now? Bonus points, is the audience eyesafe?

Show your work and equations used. Do not use the on-line calculators, you don't need them.

Answers Friday if I can find time to do the math on the road. Nobody except the "doctor" post their answers till Friday.

I assure you everything you need to solve this can be done with the static beam equation except for part 4. Its all on line.

Steve

Do your own homework. :) Here's mine:

A flat wall at 2500mm from the projector mirrors is used for this estimate. A line is scanned at 500Hz, 1100mm wide, about the best you'll get for a clean fast scan out of WideMoves for the angle capable of that scanned line. As a slow scan is more dangerous this is a good base to start with. It's the large number of people with cheap slow beamshow scanners that need helping here, so work with the conditions expected.

Inverse sine for half scan angle (To get right angled triangle to work with) of 550/2500 is 12.709 degrees, so total scan angle is just over 25 degrees.

Circumference being PI*2*Radius gets you 1090mm of arc length for Radius=2500mm. (Close to my flat-wall measure but now properly extensible for any radius once scan angle is known).

The beam is about 3mm wide at any distance from aperture to about 5 metres. (Already diverging from beam waist at lesser distance so it gets safer fast beyond that 5metres). At 500Hz, a full pass of the beam across and back takes 2ms. 3mm/2180mm is 0.001376, so the duration for a microscopic point at the centre of the scanned line is about 2.752µs. Faster scanners and greater distances will make that a lot shorter, but at this point it is mostly within range of a photodiode like BPW21, as used in a fast luxmeter circuit here: http://meettechniek.info/concepts/lux-meter.html

While a proportional photodiode will not go much faster if that one is anything to go by, could it at least give a proportional output with different power and duration at much higher speeds? If so, and it is repeatable for a wide enough variety of durations and powers, you can calibrate it for power. To get energy you need time, so what's wrong with getting that from a fast PIN diode sitting right beside it? Combine the two outputs and use UHF capable parts to prepare a signal a PIC chip can use, then calculate some worst-case figure for energy from that. Never mind spectral sensitivity, all you need to do is alert a user to a worst case state to avoid.

====

Some words about the differentiator you dismissed so carelessly. Tell me if you think this idea is stupid after you consider this carefully. A slow photodiode will not be able to respond fast enough to give you a stable power reading, so you would likely assert that it is useless for power at these short durations. But it will at least try to. A differentiator will tell you how fast its rising output is going. and if correctly mixed with a copy of the original signal, you get power. As this is a standard method to accelerate the response of a (very) slow thermopile power meter to give a good early reading, the same method can be applied to accelerate the response for a (much less) slow photodiode if you use low loss high speed electronics to do it.

You just gave me zilch in your problem to calculate if your eye safe. Nor enough to even start the problem.

You are ignoring a lot of factors relevant to the real issue of using a microprocessor for this. When we get done seeing your answers and math to the previous questions I'll talk to you. One of my problems is taken almost directly from a FDA publication on eye safety. So I can document my work.
The other is a bastardized version of a situation I know was once real.

I also have a sneaky punch I can hit you with if you don't work the problems, so if I were you, I'd get digging.
Consider yourself called out on this one.

Steve

. Quote:

"Would it not be prudent to ask Casio or one of the other commercial suppliers to get involved on the revision of the crowd scanning debate.
Casio produce a laser based video projector that people harvest components from, Mitsubishi, Coherent are also providers of such components.
Let's get some big boys on board and the HSE."
End Quote

The big laser based Cinema companies hired a few lawyers and engineers and formed their own group. They basically stated in their opening letter to worldwide regulators that they were professionals, the rules were designed for laser shows which are different and demonstrably hazardous. They further implied that laser shows are installed/operated by unlicensed, untrained professionals, unlike their systems. Based on this, they asked for their own set of rules, implied we are the bad guys, and divorced themselves from us by policy.

Sorry, nice idea but they saw the laser show industry as a threat, small potatoes financially, and unworthy/unable to help their cause. They had a point.

http://lipainfo.org/wp-content/uploa...-Pete-Lude.pdf


Steve

Not doing it unless I feel like it. I'm not doing shows. I looked at the single notion of duration and power of a moderate scanner in a moderately close range. Either what I said is useful, or it's crap, but it does at least try to come up with something. You put your demands on people doing shows, not me. As to eye-safe, at some point you're looking at a measure of power and duration. You take only the worst case into account, and specify what that will be. As to accumulation, you make that clear to a user of the device. They can usually tell if a beam is going to repeatedly hit the same spot or not.

Instead of pointing your demands at me, ask yourself this: Why, in thirty-plus years at the top of the industry, did you not see this coming and have a better answer in advance? The electrical industry has put cheap household safety testers in the hardware shops for years. This problem is tougher, but I'm suggesting that it is solvable, and I'm trying to come up with ideas about that. All you're doing is suggesting the effort is useless, that the result will be 'a toy'. What you should be doing is coming up with one that isn't.

Its all about "You" isn't it? The straw man argument fails.

I just asked you to do a somewhat humor-ized version of some problems what I had to do to pass the industry standard safety course.
Both of the cases stated below had a real world basis. I might have worked at one of them when I was young. I certainly visited the other.


You just declined to do the basic level problems the laser industry (not just shows) would have you do as Safety Course 101. The test was open book.

So much for your credibility in this manor.

For the record, I had been asking for ILDA and others to try to change the process for years, including providing hobbyist level licensing.

10 years ago the accepted and highly developed "toy" I admired had to sell at 3000$ per unit, and you still had to use it at many, many, points in the audience for each effect, because effects have hotspots. In other words it took hours, if not days, to validate all the effects in the show, to the satisfaction of regulators. The R&D, validation, and insurance costs drove the cost up. Plus the sensor was not that simple.

Doing the math speeds the required process over doing the MPE meter. Placing the scan fail system in the projector validates the math and speeds the safety case.

Lots of very skilled people with viable financial interest have invested large amounts of time in this area of laser shows. They opened their data and techniques to the industry. We rest on their shoulders. We have to do what they have worked out, there is not much of a viable option, and the science is pretty much spot on.


Steve

You singled me out and demanded others to stay out till I complied with your demands. You made it 'about me'. I tried to stay with an idea, buy you have made it personal every time you posted. Now sod off. Go find a way to spare people from the minutiae of analysis if you want them to do better. Most people who will buy a scanner these days aren't going to jump through those hoops either, and you're just going to have to find a way to deal with that if it bothers you. I think it IS bothersome, hence trying to put an idea up for consideration. I'm interested in thought from others but I'm about done with yours.

Guess what. As laser power increases, more and more regulators will take interest. This is a worry. Lasers are not following Moore's law, but they are starting to rocket up in power and come way down in cost. At some point this will become an issue.

You would not grasp the problem by doing the work. I'm not going to set here and do your design work for you. I would have helped you if you would have worked to understand what was presented to you in that problem. I just set in a room watching people who REALLY wanted to have the cert struggle for two hours to pass the test. They are the future professionals. They wish to be on the edge. They wish to improve things for others and be safe. And most of them paid for the course out of their own pocket.

Post after post, you have posted little but poorly informed opinion lately. You just had the chance to take things to the next step, but you declined.

Steve

Good for them. I'm just some punk with a wide range of interests that include lasers, electronics, and 1970's Doctor Who. I'm not studying to be a professional laser operator.

I do know enough to know that when some drug-addled geezer is climbing some lighting gantry in the middle of the night like a psychedelic spider, the pupils of those eyes might be anywhere from under a mm wide to over a cm. And you're not going to know which, or be able to police it. So your hypothetical Marilyn Monroe is a load of tosh if you think specifying an arbitrary mid-range eye pupil size is useful here to solve a general problem. I'm not a doctor but I can tell you that desire, shock, reaction to some other light, or sound, or smell, can make a pupil vary a great deal over the course of a minute or two in a live show. So you're just going to have to deal with worst case, quantify it as X, then figure out a fast detector for X that will work when some guy setting up a show waves it in front of the test projection from the closest audience position before the show to test whether the beam might be a risk to known worst case conditions. You say it's never that simple, but if there IS a worst case, and if you can quantify it, it IS that simple. If you can't do it, don't expect me to do it or it makes you look like John Cleese as drill instructor urging me to lunge at you with various mixed fruit. If you know that Python sketch you'll know who looks the silliest there.

I'm inferring from one of your earlier posts that you have tried to persuade the big boys for many years that you are serious, and not one of the dangerous loons playing lightsabres for fun and profit. If they have not been convinced by you to change the way they think in all that time, maybe you need to figure out what you did wrong. Berating me isn't going to endear you to them either. If other people aren't challenging you on this, I have to wonder if they're more scared of crossing you than of their lasers. Which would be silly because they should not fear you, and their lasers are scary. Or maybe they're indifferent, in which case you really have a problem, and the sooner you, or someone competent to do it, makes that little safety box, the better.

You just basically indirectly told every professional laser safety expert, and the self educated laser safety folks you are an absolute fool.

Ok gents, the Doctor makes his own rules it seems. He does not even want to learn how the different parts of the physics relate. Make darn sure you don't stand down range when he tells you its safe.

Another armchair expert who needs to make friends, get some exercise, and have a life, maybe try out a church?


Writing this post just feeds his need for attention.

Ok, Its a Holiday in the US tomorrow and I don't expect any responses. I'll have time on the airplane on Tuesday to write the cases for publication on Wednesday.

Loosely based on three different actual events, except the Marilyn part, that was added for fun.

Steve

Not personal, eh? :) Amazing. You;re a troll, a bigger, tree-top gorilla chest-thumping troll, but a troll all the same. Hopefully other people will recognise an attempt to suggest some answer to the problem and look at it from a a more thoughtful perspective. You seem to busy trying to belittle me again and again and again. I don't know what the scientific rationale is for that, but I doubt there is one. Keep slugging, champ. The ring is empty. And fyi, I ran several miles tonight. Can you do that? I've seen a picture of you. I suspect you can't. So don't play smartarse with me about 'getting excercise'. Keep your dumb personal speculations to yourself!

Doctor your theory is fine, but here's a real life incident - permanent eye damage from 200mw cw pointer at range:

http://www.laserist.org/2009-07_Belgian-incident.htm

Laser safety levels exist for a reason and that reason is laboratory tests have been done on eye balls to see at what levels changes occur in the cells, and then safe levels forumlated from that and other supportinmg inforemation. The levels aren't just plucked out of the air for fun.

Steve, you're being a bit of an ass-hat at this juncture from my perspective.
You are very knowledgeable, granted, but trying to show up the Doctor for the stuff he doesn't know seriously detracts from the thread direction imho. In short, you are being a bully.

From where I'm standing he has it right, but that may be the Atlantic divide.

We cannot hope to run before we can walk, and over here (and I think over there too...) we have a seriously unregulated industry. I've made this point before myself; 'anything' that makes it easier/cheaper for people to do safety, even if they're not doing it fully is 'progress'.

Thats why the safety scan lens is so good. It simply requires the numpty concerned to attach it to the front of the projector. Nothing more. The show is now orders of magnitude safer than it was previously, even without doing any sort of calculations or understanding any maths. It may still no be 'legal' or 'safe' but its a better situation than it might otherwise be.

Quote:

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If you can't do the math, which is simple. le, you wont get the gig past a safety case in the US or UK

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Can't speak for the US, but in the UK I could've written a load of nonsense in my safety record for a number of gigs and it wouldn't have made a blind bit of difference to the approval or not.

A not so simple set of time tested, peer reviewed, very conservative assumptions are used to make the calculations workable. If you accept them, its not hard to "plug and chug" to solve this equation. The real trick is to keep the units consistent.

7 mm is not a bad value, it is the accepted, peer reviewed value. its there for a reason.

What causes the problem is the way the Laser Safety equation is written and explained. It looks some Alien character set. With Phi and Theta so close together, you might as well toss in an Omega and really confuse people. No one wants to mess with the mathematical gobledegook around it.

Therein lies the problem, getting the word out on what to change to make an effect safe.

Steve

Quote:

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Originally Posted by White-Light

Doctor your theory is fine, but here's a real life incident - permanent eye damage from 200mw cw pointer at range:

http://www.laserist.org/2009-07_Belgian-incident.htm

Laser safety levels exist for a reason and that reason is laboratory tests have been done on eye balls to see at what levels changes occur in the cells, and then safe levels forumlated from that and other supportinmg inforemation. The levels aren't just plucked out of the air for fun.

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I didn't have a theory. :) I understand that empirical tests are done on actual eyeballs. So isn't it possible to find a worst-case, then determine duration and power and wavelength that does it, then build a cheap widget that will detect it to warn people? The idea being that for any wavelength, pupil size, whatever, other than worst case, things will be safer. No doubt this could 'enforce' some very low MPE values, but it wasn't me calling for them to be raised. Nor have I ever made any pronouncement about laser safety either generally or specifically, despite Steve's claims. I stay well out of that talk, for good reason. I only asked here if there could or should be some kind of MPE warining widget because it's now clear that the 'thin blue line' trying to police this stuff is so totally overstretched that it ought to welcome any suggestions that might raise the issue's profile, if nothing else! I even made the suggestion that a photodiode with proportional output can be accelerated by differentiator. It works for power meters, so should be considered in this context.

For what little it's worth:

Part one.
First, laser diameter at 1234 metres, by transposing the Wikipedia expression for divergence gives 2.0353 metres as beam width. Area of illumination is 3.253471 square metres. 25W spread like that is 7.6841 W per square metre. 7mm pupils have area 0.0000384845 square metres. Ratio of areas is 0.0000118, which multiplied by 25W is 0.295 mW. So Marylin is eye-safe, and the exposure class at her face is class 2M because the beam is so wide, and because if it lights her up it must be visible.

I suspected she was eyesafe anyway just from having seen how big a beam at 0.5mr gets after just a few hundred feet. By playing the man, not the game, as good chess players apparently do, I assumed his bunch of youthful geezers is a very studious gathering who know exactly what they are doing, despite his attempts to make us assume they are dangerous morons, so the numbers don't surprise me.

Part two.
25W must be spread over as little as 50 cm2 to get as much as 0.5W per cm2. Diameter would have to be 7.9788 cm. Subtract 0.08 cm at aperture, so 0.078988 metres used in transposed Wikipedia divergence expression gives a distance of 47.8715 metres for burn risk.

Part three.
I quit at this point. Here's why:
http://www.optique-ingenieur.org/en/...ontenu_09.html
If wavelength is important there, they didn't say, you presumably have to plug in all that MPE bit got from somewhere else as if there isn't enough unwarranted opacity there already! I went as far I was willing to. No-one's ever going to have to run crying from my lasers. And not everyone on PL is trying to act like a daredevil flying a plane under a bridge. Come to that, not everyone admires the fools who do. When I take risks I prefer not to subject others to them. So I may die alone one day. But who doesn't?

There is already an easy way of setting MPE - Some pc based power meters allow you enter in the sensor diameter and once this is set, can be put into mw cm 2 display mode. They will then autoatically display the read power in mw cm 2 with no calculation needed on behalf of the user as the meter calulates it internally on the fly.

So all you need to know is your published sensor diameter and all you need to do is ensure the meter is in that mode and the beam fully covers or overspills the sensor. Almost idiot proof.

Excellent. Now if the big show guys want to impress the legislature, all they have to do is the mother of all group buys and build the damn thing for everyone. :)

It can already be bought off the shelf for less than a physical meter - around £800 including the sensor (although the price does depend on what sensor its paired with).

It's being evaluated on my behalf atm and if its any good I was thinking of buying one and posting a review here.

I haven't mentioned it before because I'm awaiting the verdict from those in the know.

Hi Doc
I think on this post you missed the point I was trying to make. There are current products available that exceed the MPE for home use that are available, lets get some people on board like Casio or Sony to revauate the original bunny data. They have the budget to do this.
We as individuals don't.
I'm not doing this for profit, everyone who knows me, knows that I want to expand technology and create new concepts.
We do however have to ensure that commercial products that can cause detrimental health issues, that could be attributed to our industry are highlighted.

Hi James
The AOR directive sets out in the onset to cover visible, Uv and Ir.
The mandate for this was set back in 2005.
I agree this was a backstep, but the HSG 95 was always about safety, I have never said it was about crowd scanning.
The HSG 95 was a guideline set up using Data based on Ion laser tech and not point light source emissions.
However I'm sure with all the work that's being done and the new articles that have been made available regarding the collateral radiation emissions, we'll see some new values soon.
I am with everyone on here in regard to the blatant disregard for safety that happens sometimes.
This is purely down to some people using technology they don't understand.

Quote:

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Originally Posted by Laser Electronics Ltd

Hi Doc
I think on this post you missed the point I was trying to make. There are current products available that exceed the MPE for home use that are available, lets get some people on board like Casio or Sony to revauate the original bunny data. They have the budget to do this.
We as individuals don't.
I'm not doing this for profit, everyone who knows me, knows that I want to expand technology and create new concepts.
We do however have to ensure that commercial products that can cause detrimental health issues, that could be attributed to our industry are highlighted.

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Sounds good to me. If Casio (and of all firms, those guys could really do this) make some cheap way to get an MPE meter together for general public use, it can help. I won't repeat myself, I'll just say that 800 quid is a hell of a price for guys who'd rather buy Chinese lasers for cheap, and are scared of spending over fifty bucks on a diode driver. :) It needs to cost about the same as a good first aid kit, or a small CO2 fire extinguisher at most. We could argue all day that priorities are not what they should be, but human nature being what is is, maybe it's easier to build that box. Eventually I'm sure someone will, too. If it happens before governments start shoving people around, so much the better. More freedom that way.

There is always a laser check (Coherent) or some of the more diy meters. The problem then comes though not from using it but understanding how to make the calculations. Anyone can read the power, very few can calculate MPE, myself included.

I do agree a £100 MPE meter that you simply chuck into the beams and get mwcm2 values out would be nice, but even then you'd have to know to fill /overfill the whole sensor (I wonder how many home users would take a reading with a partial sensor if the beam was too narrow and they didn't have lenses?), plus I've not seen any indication that a cheap accurate mass produced meter is even possible for those sort of prices. Even 2nd hand commercial sensors without a meter seem to come in at £200-500 on ebay depending on the sensor.

If Casio could come up with the MPE meter equivolent of their maths calculators, everyone would be laughing. I think the issues though are low volume, cost and the fact that they've never seemed to want their diodes to be used in lasers in the 1st place - I seem to remember users posting stories of them allegedly increasing security in their cinema projectors several times to try to prevent harvesting, things such as security screws and even epoxies.

The AOR Directive contains two sets of limits; coherent and non-coherent optical radiation. The 'coherent' limits are of course for laser. The exposure limits published in HS(G)95 didn't exclusively come from ion laser sources. They are the standard coherent limits derived through ICNIRP at the time of publication, which, slightly confusingly, also cover UV,vis, and IR.

Re Casio and the like, I'm still not really understanding why they would have any interest in getting involved with a problem that has nothing to do with the intended use of their own products. The risk associated with devices that use laser sources to create a homogenised output is completely different from that of a flying-spot projection device. This is why laser projection manufacturers have teamed up to form their own association, and there is separate IEC laser safety standard in the works for this type of device.

Maybe Laserscope should be invited, because some people poorly hack their products and sell them as laser show projectors... The point being, it is not the component manufacturer, (and less so, when it's a finished product being bought and ripped apart for components), that has the responsibility. It is the manufacturer/supplier of the final product, that makes it available for market that has the responsibility to ensure it incorporates the minimum safety features and user information.

Hi James
Find below the replies to your post, not in chronological order but in relevance.

If you take a current Casio video projector that uses 20+, 3 watt 445nm laser diodes as their primary light source that is spread over an aperture of 3cm, do you not think the power density is greater than the current HSG95 regs, and have you actually measured it.

This is a product that is commercially available, I was only making the association that people use these components because they have been made available commercially.

Your comment about LaserScope is noted, but is not relevant, they have never made a product that is commercially available to the general public, they have always produced equipment over the latter years for medical and research.

The HSG95 as you know was an update to the PM19 document, there was no new research included except from the Military Laser Safety committee that was implemented regarding the use of Q-Switch/Quasi Pulsed laser and Point Emission Light Sources from data researched from 1993-1994.

Is the significant difference with projectors that the light is very much non-coherent by the time it gets to the aperture?

Hi Norty
No the light from most current commercial LVP's maintains its coherence, this is why you dont have to focus the newer video projectors very much.

Most readers will agree that if you take one of the 24 laser diodes from a Casio laser illuminated projector (LIP), add the typical optics people use on this forum, and aim it at a piece of card several metres away, you'll soon end up with a hole appearing and a burning smell. We all know that if you aim a fully functioning Casio LIP at the card from the same distance, there is no resulting damage.

Why is this so? The MEMS/DLP element in the projector acts as a diffuser, significantly altering the properties from the blue laser sources before they reach the output aperture. This is the reason that the retinal thermal hazard of all the combined embedded sources is substantially less than that of single unmodified source.

The exposure limits in HS(G)95, (which is guidance, not a regulation), are not really suitable for evaluating sources of this type; exposure limits expressed in radiance is the better way to go. There is an IEC committee currently working on a safety standard for LIP devices. The limits in the standard are expressed in radiance for the retinal hazard regions for this reason.

I haven't tested a Casio device, but have the radiometric data from a 5000 lumen LIP, and the retinal thermal exposure puts it into a RG2 grouping. i.e. direct exposure does not pose a hazard due to the aversion response. The same could not be said for viewing one of the single unmodified laser diode sources!

I made the Laserscope association, because in post #9, the concern being expressed about Casio was the fact they had introduced to market a product that was being used for harvesting laser diodes.

If Casio were making flying spot laser projectors, I agree that it could be useful for them to get involved, but hopefully you can now appreciate that, although the figures used for the embedded lasers appear quite alarming, the output beyond the aperture is not. And can therefore see why the likes of Casio would probably have little interest in getting involved in a problem that is not relevant to the normal use of their product.

James

Sorry to bump this again (as if mentioning it twice in two days isn't enough..), but I think I have a good enough reason to post directly to it..

In a couple of threads in the same two days, there is talk of damage to CCD's from lasers during shows. I understand that it may be the newer, more expensive low-light sensitive devices that are most prone, and perhaps also those with large lenses. Anyway, whatever the cause, isn't this worth exploring for an MPE meter? It will take a lot of research that is far beyond my means, but I have some notions worth following up:

If a quantified exposure is known to produce some aberration, regardless of sensor response speed, it may be that taking a 'before' and 'after' image pair can be used to detect pulses above some threshold for energy, regardless of power, and that lateral extent may possibly allow inference of beam width.

Even if beam width can't be inferred that way, (I imagine a laser beam would focus down to a spot size based on wavelength rather than beam width if focus was optimal), there could be another way to do it in combination. If some replaceable element were designed, then damage could be collected and examined later, perhaps milliseconds later, by analysis of two image frames, and the element would be replaced before it became exposed to the point of giving poor readings.

All the above is assuming that some cameras are damaged even by eye-safe laser light, which according to observations in other threads, some of them may be.

EDIT: Instead of 'inferring' anything about beam width, just stick a lens cap on the camera. As 7mm seems to be the standard pupil size for MPE measurements, it is cheapest to drill a 7mm hole in a lens cap! (And some finer holes to detect those beams that are inadequately diverged).

I wish it was so easy with CCDs. When you use one for beam profiling, it takes skill, and manual adjustment to set the gain and gamma correctly to get a good reading. Their dynamic range is huge, but when you digitize with one close to saturation, it takes quite a bit of adjusting and fiddling with either the laser power or the camera settings. There are also issues with the readout timing, most of them do not do progressive scanning for a full frame, but do techniques with individual odd and even fields. Then you have fun with electrons spilling out of the wells and into the readout circuits on chip, usually resulting in saturated bars in the image. Most cameras do not have a global sample and hold, either. usually we set the profile thresholds for 90-10 or 84-16 edges.

With a non-Gaussian beam, the photodiode makes short work of this, compared to a CCD.

Without care and manual adjustment, its not something I'd trust my eyes to. Certainly not with a 8 bit video digitizer, or even with a 10 bit digitizer. 10 is about as good as it gets with a prosumer camera.


I'm the proud owner of a Spiricon Beam Profiler, which uses generic stock CCD cameras. When I try to use it with pulsed/scanning lasers, its hopeless without sync pulses supplied from the laser. The camera, if free running, samples in a manor analogous to lissajous patterns, but in intensity, not space. I still have three sliders on the Spiricon to set video digitization settings, so my subjective judgment can alter the beam profile.

There are some techniques for extracting edge threshold from a repetitive pulsed wave across a photodiode, ie constant fraction techniques. However you still need variable gain on how you process the photocurrent, and therein lies the issue. This would not deal with a single shot or single flash effect.

I wish it was that simple, really I do, but 10 bits does not work.

The simplest analog MPE meter ever made worked with a single wavelength, and stored the differentiated pulse in a carefully designed inductor that mimicked the eye response curve. A slow microprocessor then grabbed many pulses, measured the timing, and did the math. It then dumped the inductor as needed.

Steve

Ok. :) Silicon IS complex, no doubt about it.. But how about this:

Some simple chemical film that is adequately sensitive to gentle destruction, and simple to characterise for MPE measures, then have some CCD watching that in some small chamber? If you can take bafore/after images that way the CCD need not take direct stress, but only take images of that film the way 'nature' intended.. While I don't doubt that this is no way to replace observations of the innards of the average eyeball, might it not be consistent enough to read for MPE given simple aperture limits on entry to the chamber?

Edit: Bit more thought on this one... If a fast photodiode detected the pulse, an otherwise shuttered-off CCD (with imaging lens) could have its shutter triggered open to take an image of the sensing film. It would have to be a very fast shutter in case a new beam arrived early enough to threaten the CCD, but the idea is that it might keep a CCD safe from the incoming light more often than not, and each capture prompted by the fast photodiode would be the 'after' image, and the 'before' for whatever came next. Software comparison of the images might be fast and maybe also easy if the sensing film was useful enough to do this. There may even be retinal cells made in labs that can help with that film, but I bet there are higher priorities for those right now..

A good rule of thumb here is that if damage occurs to ccd (charge coupled devices ) then it is not eye safe.
Unlike earlier laser devices the point source light isn't dissipated, the reason more issues are now occurring is because short cavity laser diodes produce higher levels of Ir and Uv between electron emissions of E1-E2 during the decay stage that causes phase conjugation from e1 to e2 during the decay rate for photon emission that isn't being controlled.

In Ion lasers you would use a magnetic field, We cross modulate and phase modulate the pump source at substrate level in all our systems, the only drawback is for light show use, we have to make the beam slightly bigger.

Hi James
In answer to the Why is this so? I'm surprised you asked that.
The generated light source is expanded and then re-collimated after the DLP.
A DLP device doesn't act as a diffuser but a multi segregated mirror deflection device.
Therefore the coherence maintains and this is why if multiple mirrors are engaged within the DLP that allow light emission, the MPE is exceeded.

It was a rhetorical question Clive.

I’m afraid your assumptions and statements are wrong; the retinal thermal emissions from such devices are nowhere near the levels to cause the harm that even a low power laser direct exposure could result in.

Just this week there has been a five-day meeting of the IEC Optical Radiation Safety and Laser Equipment group in Frankfurt. Experts on this subject, from the world over, convened to discuss a whole range of issues. The topic of LIPs was covered in several sub-meetings. There are two very relevant facts from these meetings:

1) In the soon to be published new version of IEC 60825-1 (Ed.3), there is a radiance exemption clause. This exemption comes about because the harmful aspects of the original laser light source(s) is destroyed in the process that these LIPs devices, (which includes the Casio type device), use to create and project an image.

2) The other thing to come out of the meeting was further progress in the mature draft for a new safety standard for such projectors, which among other things, serves to differentiate these image projectors from more hazardous flying spot projectors that have more similarities with traditional laser light show projectors. The optical output characteristics of these LIPs devices are so far removed from traditional laser sources, that the new standard is not even part of the ‘60825 (“Laser”) series of standards and technical reports.

If what you were saying was correct, then there would of course be no need for the IEC to define the exemption or the completely new safety standard describing LIPs methods of projection.

James

Hi James

I didn't make any assumption, my statements were based on work done.

The retina absorbs coherent emissions and as such a point source light that is polarised in one axis H or V .

I'm aware of the meeting and as such your also aware of the arguments if you attended.

The lips (laser that illuminated a micro display area or laser illuminated projection system) also uses a DLP (digital micro mirror device or digital laser projector) these systems when viewed are way above the MPE levels in their current state.

As I've said before give me a call to discuss this.

Thanks

Clive.