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Thread: Using a concave lens to increase divergence - picking the right strength

  1. #11
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    As a related aside, what is the 100x MPE safe exposure reading for an 8mm diameter pupil?

    ILDA always publish it as 100x MPE or 100 MW/cm².

    However, as this means nothing in the real world to many people (without calculating and as this relates most relevantly to the simple method) I've always wondered why they don't publish the standard as dual bracketed figure of 100 MW/cm² (XXmw / 8mm diameter) given that the pupil diameter is always an assumed constant.

    Would make it much easier and safer for end users to implement if the figure was also quoted as a figure they could simply go out and use with a power meter with an 8mm sensor area. Obviously if sensor size if slightly different to 8mm eg 7mm (I'm not sure what the standard aperture is, then the figure could eg be quoted in terms of 100 MW/cm² (XXmw / 7mm diameter laser power meter head). Point is to make it easy for the end user to implement with a standard sized power head.

    It takes away the risk or complication of further erronous calculation introducing end user errors or the risk of the end user interpreting 100 MW/cm² as 100 MW/ sensor reading.
    Last edited by White-Light; 03-28-2010 at 03:18.

  2. #12
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    100Mw/cm2 will even fry your brains


    The MPE for your eye calculated with a blink response of 0,25 seconds = 2,5mW/cm2

    A MPE for typical slow scanning beam (0,01s) = 10mW/cm2 this is what "they" call MPE

    But for a fast scanning show where the pulse duration is "only" 18microseconds the MPE = 27mW/cm

    Now with the new simplified method they are talking about 10MPE which is considered relatively safe then they refer to 10x the standard MPE = 100mW/cm2

    All these MPE values are measured with a pupil diamter of 7mm


    1 When there is some ambient lighting (there always is) and your pupil is 5mm instead of 7mm the exposure is reduced by 50% and the pulsetime is reduced by 30

    2 In the real world you also have things called adverse reaction where the pupil get smaller, and the head is turned away.

    Those last two parts are the main reason why no accidents happen with the many high MPE shows you see everywhere.

  3. #13
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    Thanks for the reply. I was talking about the 10x mPE standard but typed 100x MPE by mistake (I keep getting that confused!).

    It was that which I was referring to when I said it might be easier for ILDA to quote a dual figure of 100mw/cm2 and another figure based on the average sensor diameter so that all anyone needed to do to use the simple method was check their sensor diameter against the stated ILDA diameter as quoted and take a straight measurement (no calculation needed that way provided your sensor was the standard size).

  4. #14
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    Take a small piece of metal, drill a 7mm hole in it and put it in front of your detector.

    If you read 3,6mW you are at MPE

    36mW = 10MPE

    Its that simple, but you need sensitive head, most thermal meters are not that accurate in the mW range.

  5. #15
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    Thanks ........

  6. #16
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    3.6mW through a 7mm aperture is not the correct MPE figure to use. Any system that does not have an effective scan-fail and a means of ensuring the effective pulse duration and repetition rate for the chosen MPE are not exceeded, should be using the 25.4W/m^2 irradiance, as the maximum exposure. Which means just under 1mW through a 7mm aperture. On the common Lasercheck, the detector size is 8mm, so this means the reading should be no greater than 1.27mW.

    One thing people in the UK and Europe should be a bit careful of is stating that they are using the ILDA 10x MPE or 100x MPE. For to do so, at the moment, in some member states, and across the whole of the EU as of the end of next month, is stating that you are committing a regulatory offence.

    ALDA (sorry ILDA) appears not to have told its members that in the EU there is a new regulation coming into force on the 27th April that effectively makes it a criminal offence to exceed the MPE, which is quite a surprise given how many of its members are European, and are therefore directly effected by this new legislation. The ICNIRP guidance figures that we have all been using as guidance in the past, are set to become the legal limits.

    Now whether we think the levels are correct or not, is neither here nor there unfortunately. They are what they are, and will, (if not already in some parts of the EU), become the mandatory limits.

    So it’s probably worth just being aware that putting it in writing that you are working to levels 10x the legal limit may not be such a good idea, in terms of insurance cover, or in the event a steward or member of bar staff etc wanted to claim that their eyesight had been effected by the laser effects.

    James Stewart.

  7. #17
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    that effectively makes it a criminal offence to exceed the MPE
    Ouch!
    I'm surprised there hasn't been a bit more noise about this on the forum then.
    Can you provide the details of the new regulation so we can read up?

    However, I guess that any changes will only be as good as any enforcement, and opertors will continue to do their own thing regardless of guidelines/law

  8. #18
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    Maybe ILDA need to revise the standard naming then so 10x MPE becomes the new MPE standard and what was MPE becomes the old standard.

    Someone at ILDA clearly needs to contact the EU beaurocrats and liaise with them over this issue before the new standard becomes effetively outlawed by Eurocrats using an out dated standard.
    Last edited by White-Light; 03-29-2010 at 05:59.

  9. #19
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    OK, I’ll answer briefly on this thread, as I don’t want to hijack what is an excellent topic about altering beam divergence. I suppose if this is something people want to speak about more, then it’s only fair to start a new thread.

    The new European legislation comes from the EU Directive 2006/25/EC. And as the numbering scheme suggests, this has been simmering on the back burner since 2006. The full text can be downloaded from:

    Physical Agents (Artificial Optical Radiation) Directive 2006/25/EC

    http://eur-lex.europa.eu/lexuriserv/...n0038 0059.pdf

    As with most of these types of document, it is a good cure for insomnia. ☺

    The goal of the legislation is to provide a minimum level of safety to workers where harmful light sources may be used, in a way that is uniform across the EU. It is therefore up to each member state to implement its own set of rules that meet the requirements of the ‘Directive’. In the UK we are set to have this implemented with the new ‘Control of Artificial Optical Radiation at Work Regulations 2010’ which where published for consultation back in November 2009. Other countries will have their own equivalent regulations. And they may already be in force. France and Romania are two countries I know that have already implemented AORD.

    You’ll see that the directive not only covers lasers, but also non-coherent light sources. Initially there were concerns how this would impact the theatre and performance industries which use a wide range of high brightness light sources. But the research so far is indicating that the limits are not going to pose any significant problem. And as bright as some of these other sources may ‘appear’, none come close to having the same power densities of even a modest laser beam.

    Unfortunately ILDA does not ‘set’ the standard on MPE limits. An ILDA ‘recommendation’ is not an international safety standard. It never was. It was just a recommendation. ILDA has no regulatory authority to issue safety standards, for they are only a trade association. The MPE data is produced by an international scientific organisation called ICNIRP. It is the EU parliament that has decided upon these values as the legally binding limits.

    Unfortunately ILDA have been aware of this legislation for a while. I mentioned it to their safety chairman and director following the Russian incident, but received a rather dismissive reply. (hence my quip in my earlier post referring to them as the ‘American’ rather then ‘International’ Laser Display Association)

    Patrick Murphy was also here in the UK in September last year, talking about ILDA’s recommendation at a safety meeting where the EU directive was also spoken about in great detail. At the time I did point the potential problem with ILDA recommending to its membership in Europe the x10 MPE issue, and what it could mean it terms of liability. However, I’m sure they have their own plans on how they are going to advise members on staying within the law.

    I’m actually not against the x10 MPE proposal itself, if it is used with reliable equipment and well thought out shows (e.g. no slow moving finger beams from multi-Watt lasers at close quarters). But my point was that people need to be a bit careful about how they approach this if they are not to be seen as irradiating people in excess of the new workplace exposure limits.

    Sorry it turned out to not be so brief a response.

    James.
    Last edited by JStewart; 03-29-2010 at 07:02. Reason: URL edit

  10. #20
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    Could you PLEASE post a new topic about the new Legislation in europe.

    Most of us did not know about this but its mendantory information.

    Thank you.

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