Mounting lasers on stage

[smokeAndMirrors]

Steve covered this topic already. The performers of course were trained with the safety of the lasers behind them as were the crew. (I should know, I worked on the lighting for that tour in the US)

Respect!

So how were the lasers mounted?

Unfortunately, however, they have dropped the lasers from the show this year. I am unsure of the specifics, but it might be due to the Barco projector they fried with the laser.

Yeah I saw The Wall tour this year, light show was a bit disappointing to be honest. To make up for it I am seeing this tomorrow

[Jem]

Ahhh... So, i'm guessing you're in the Cambridge area then

Well then, you'll be delighted to know that Cambridge is one of the areas in the UK where the Council is pretty knowledgeable about lasers. I believe it is not uncommon for one of the Country's top laser experts to just 'drop in' on a show where lasers are being used.

We have another forum member in that area who is well aware of dealing with this gentleman at laser shows (I have no doubt he'll step in to this thread if he wants to ). I think this is developing into one of those occasions where you will *really* have to make sure your paperwork is in order and that you are doing everything as you should be.

Incidentally, there's no-one trying to frighten you off here, it's more just a bit of good advice to save you hassle in the long run

Take care

Jem

[smokeAndMirrors]

Ahhh... So, i'm guessing you're in the Cambridge area then

Well done Sherlock!

Well then, you'll be delighted to know that Cambridge is one of the areas in the UK where the Council is pretty knowledgeable about lasers. I believe it is not uncommon for one of the Country's top laser experts to just 'drop in' on a show where lasers are being used.

Well at least the Council are good for something then.

We have another forum member in that area who is well aware of dealing with this gentleman at laser shows (I have no doubt he'll step in to this thread if he wants to ).

That would be interesting. Mind you, Cambridge is poorly served for smaller music venues that support any sort of light show, never mind lasers, so I tend to work out of town.

I think this is developing into one of those occasions where you will *really* have to make sure your paperwork is in order and that you are doing everything as you should be.

There seems to be an assumption that it is not. Which may or may not be the case, but...

Incidentally, there's no-one trying to frighten you off here, it's more just a bit of good advice to save you hassle in the long run

...the lectures started even before you knew my level of experience and I'd asked an elementary question about mounting. Of course I don't want hassle and I aspire to wow my customers, not blind them; your help is appreciated, but by the same token I have always realised that lasers are not toys and can be dangerous; even the lower-power lasers I've used for small gigs before have been directed way above heads avoiding reflective surfaces and so on, even if the band and the venue were blasé about the safety aspects (which they were). So whilst I think no-one's trying to frighten me and you're all smart and well-meaning and that I could (and want to) learn a lot from you all (and already have!)... you could be just a little a bit less intense with the sermons.

[Jem]

Oh dear... Sorry, I didn't mean to sound patronising

This is one reason why it's a *very* good idea to introduce yourself on the forum and tell us a bit about yourself, your experience with lasers and the general area where you live. By doing that we can then pitch answers that are meaningful to your particular situation without being condescending.

Without this knowledge, I guess there is always the assumption that you are new to the game and the answers are pitched accordingly.

Hope we haven't offended you

Jem

[smokeAndMirrors]

Oh dear... Sorry, I didn't mean to sound patronising

I know you mean well, and from the quality of your replies and the obvious vast experience the posters have here, if I ran off in a strop I'd be the loser. And I'm really glad I was taken to task on the "scanning frequency" point because I don't want to make mistakes that result in people getting hurt, and I'm glad that it came up even if it was a bit OT.

This is one reason why it's a *very* good idea to introduce yourself on the forum and tell us a bit about yourself, your experience with lasers and the general area where you live. By doing that we can then pitch answers that are meaningful to your particular situation without being condescending.

I joined ages ago, but my work was sporadic, I fell out with the band I was working with (they turned quickly from a bunch of decent guys to would-be-rock-stars and dumped heavily on me). Since then I've done one video shoot for my own band, but I have just formed a working relationship with a new band and I've just acquired my RGB laser so I feel that I've stepped up a rung in the ladder, not least in terms of the output power of my laser. With regards to the lower-power devices (280mW RGYs that I have) there is a bit of a lax culture but I realise that at 600mW my new box is capable of doing damage, even burning skin.

(Incidentally, I saw Jean-Michel Jarre this year, who seemed quite happy to stand in a static scanned white fan for some period of time and I'm guessing his lasers were 3W or above so what gives there?)

Hope we haven't offended you
Jem

No, I appreciate your comments. But I also want an answer to my question, which seems to have taken a back seat to the H&S issue.

[Adrian Cavaleru]

Hi Dan, the first of those two looks incredibly flimsy. You need something much more substantial.

I have two truss clamp positions on my RGB that I use where possible, but also use a tripod when it's the best option (bearing in mind what Steve said about vibration and movement; I would only use the tripod on a solid concrete stage).

I think Carl B uses the mounting method that you described but I have installed the top hat mount in to the chassis of the projector, and from memory your toblerone has an extremely solid frame so maybe that's an option?

both may be good.
I should think about a way to rig the projector on that stand.

[buffo]

This is one reason why it's a *very* good idea to introduce yourself on the forum and tell us a bit about yourself, your experience with lasers and the general area where you live. By doing that we can then pitch answers that are meaningful to your particular situation without being condescending.

Well put, Jeremy. Yet so many new users omit this crucial step. (And worse, they then get testy if we assume that they know less than they actually do!) Here's a tip to all new members: FILL OUT YOUR PROFILE INFORMATION! Most people will check that first before replying to a new member. If you don't give us anything to go by, we will assume the worst.

Incidentally, I saw Jean-Michel Jarre this year, who seemed quite happy to stand in a static scanned white fan for some period of time and I'm guessing his lasers were 3W or above so what gives there?

Did you miss the post by MixedGas where he explained that trained crew members can be exempted from the rules if proper safeguards are in place and they've signed a wavier?

Considering that Jean-Michael Jarre's entire act consists of him interacting with his laser harp, it's pretty clear that he qualifies as a "trained crew member".

I also want an answer to my question

Doc's solution sounds reasonable. I've used tripods with that sort of mount before with no problems. But if you're dead-set against tripods, then what about Mliptack's suggestion?

And worst case, if you absolutely need them on the floor, then why not build a wedge-shaped wooden box with an angled top that you can set the projector on/in?

Adam

[smokeAndMirrors]

Well put, Jeremy. Yet so many new users omit this crucial step. (And worse, they then get testy if we assume that they know less than they actually do!) Here's a tip to all new members: FILL OUT YOUR PROFILE INFORMATION! Most people will check that first before replying to a new member. If you don't give us anything to go by, we will assume the worst.

Fair enough.

Did you miss the post by MixedGas where he explained that trained crew members can be exempted from the rules if proper safeguards are in place and they've signed a wavier?

Yes, but a laser rated at more than 1W firing a relatively narrow beam is going to cause skin damage irrespective of whether anyone's signed a waiver or not (heck the HS(G)95 says .5W will cause problems).

Considering that Jean-Michael Jarre's entire act consists of him interacting with his laser harp, it's pretty clear that he qualifies as a "trained crew member".

He wears gloves for the laser harp. I'm referring to the show intro:


Doc's solution sounds reasonable. I've used tripods with that sort of mount before with no problems. But if you're dead-set against tripods, then what about Mliptack's suggestion?

And worst case, if you absolutely need them on the floor, then why not build a wedge-shaped wooden box with an angled top that you can set the projector on/in?

Adam[/QUOTE]

[Doc]

I believe by "relatively narrow beam" they are refering to pencil beams.

That is a pretty wide fan in that shot, the energy density in such a fan is unlikely to cause skin burns, even with 5W+ though I wouldn't recomend on axis viewing.

[buffo]

Yes, but a laser rated at more than 1W firing a relatively narrow beam is going to cause skin damage irrespective of whether anyone's signed a waiver or not (heck the HS(G)95 says .5W will cause problems).

The half-watt threshold for skin damage is for a static beam. The picture you posted of the show's intro is a wide fan. Scanned patterns are completely different. As Doc already mentioned, in that instance you wouldn't need to worry about skin damage even with 5 watts of power.

Adam

[Jem]

I was also at the JMJ gig, as were quite a few others on this forum. What I can tell you is that the show was done by Hugo Bunk, a very well established and well respected laserist. I can also tell you that the lasers used were multi-watt OPSL with remote fiber optic fed scan heads.

I can also tell you that the person responsible for laser safety on the entire UK JMJ tour was James Stewart of LaserVisuals, who incidentally is also a member of this forum (even though he doesn't post very often). I can also tell you that James is an incredibly well respected person with vast amounts of experience. He is absolutely, unquestionably, categorically as straight as a die and does everything exactly to the rules. For instance, if you went to the London JMJ gig you would have experienced audience scanning. However, if you were at Manchester you would have noticed the distinct lack of audience scanning. This is because it was deemed unsafe in that particular venue as the safety criteria could not be met.

I therefore have no doubt in my mind that the JMJ lasers were absolutely safe

Incidentally, LaserVisuals run safety courses from time to time... Well worth the money for the experience gained.

Jem

[smokeAndMirrors]

Jem, I wasn't implying that the show was unsafe. I was asking for an explanation of why it was safe. Please don't be so aggressive.

As for the Wembley Arena shows, there was no scanning that I was aware of, it was all 15ft above my head, but that could be just where our seats were... Jarre says this on his blog:

"Finally the concert in Oslo started sounding and looking close to my expectations. There is something special with this venue, the audience (who was really great that night, many thanks to them) is really close to the stage, and it gives a feeling of proximity quite unique. In addition you don't have these far too strict regulations like in Sweden for lasers, so the audience could be truly immersed in the waves of light."

so they were clearly scanning at some venues.

[mixedgas]

How is J.C.OH these days. I thought he just did theoretical and enjoyed shows. Didnt know he popped in doing inspections.......
Met him a ILDA and LFX a few times, great guy.
Steve

[Jem]

Jem, I wasn't implying that the show was unsafe. I was asking for an explanation of why it was safe. Please don't be so aggressive.

Aggressive

I've just re-read my post and I don't think it was aggressive. Succinct, informative and to the point perhaps, but aggressive?, nah.

As to why it was safe...

Well, every aspect of the show was carefully risk assessed, measured, MPE's measured, considered, and finally when all safety criteria had been met it was passed off as safe for public viewing... and as safe for the performers.

Jem

[smokeAndMirrors]

Aggressive
I've just re-read my post and I don't think it was aggressive. Succinct, informative and to the point perhaps, but aggressive?, nah.

There was - to me - clear implication that I was alleging unsafe procedure. "I can tell you..." repeated several times, and allusions to slights on the reputations of individuals involved. Or you were simply name-dropping to impress me And yes, I'm impressed!

As to why it was safe...

Well, every aspect of the show was carefully risk assessed, measured, MPE's measured, considered, and finally when all safety criteria had been met it was passed off as safe for public viewing... and as safe for the performers.

Jem

That's a legal answer, not a technical one. Specifically I wanted to know how it was safe to stand in a fan from a powerful laser. From LaserSafe, a fan has higher energy density than any other scan pattern (all other things being equal). If you'd said "the distance to the emitter and the scan angle sufficiently attenuate the radiation" you'd have answered my question. Your actual answer was pretty much "it just was, ok?".

[Jem]

Your actual answer was pretty much "it just was, ok?".

Ahhh... I feel that the lack of emotion in the written word is coming into play here. This is one of the problems with forums, it's not always easy to express feelings and emotions in simple text.

You are obviously quite a sensitive person who has simply misinterpreted what I was saying and misconstrued it as me being offhand. Nothing could be further from the truth, i'm quite a nice guy, honest

As for name dropping... Never even crossed my mind. I guess you must be easily impressed

[smokeAndMirrors]

Ahhh... I feel that the lack of emotion in the written word is coming into play here. This is one of the problems with forums, it's not always easy to express feelings and emotions in simple text.

You are obviously quite a sensitive person who has simply misinterpreted what I was saying and misconstrued it as me being offhand. Nothing could be further from the truth, i'm quite a nice guy, honest

As for name dropping... Never even crossed my mind. I guess you must be easily impressed

Och, sometimes I don't so much get the wrong end of the stick as the wrong stick Sorry if I was snippy.

And yes, I am easily impressed by people who know what they're talking about.

[Jem]

And yes, I am easily impressed by people who know what they're talking about.

Oh Damn, that counts me out then, I guess i'd better shut up

[buffo]

a fan has higher energy density than any other scan pattern (all other things being equal).

Not quite. A fan has higher energy density AT THE VERY ENDS OF THE FAN when compared to all other scanned patterns, since at the ends of the fan the mirror has to make a 180 degree turn, which is (obviously) the largest turn it can make, thus you have the highest "dwell" time on a single point while the mirror reverses it's velocity. But the center of the fan has the same energy density as any other scanned image. (You'll also notice that the performer is not standing at the edge of the fan in that picture.)

But really, all this is irrelevant when you're talking about *skin* exposure (which has a much higher threshold for damage). Even at the ends of the fan, the power density is nowhere near as high as you would have with a static beam. So long as the beam is scanning at a reasonably fast rate (30Kpps, let's assume), the fan is many orders of magnitude safer than the static beam - even at the ends of the fan.

Adam

[allthatwhichis]

Ahhh... I feel that the lack of emotion in the written word is coming into play here. This is one of the problems with forums, it's not always easy to express feelings and emotions in simple text.

That's what the smileys are for...

[danielbriggs]

Hi Dan, the first of those two looks incredibly flimsy. You need something much more substantial.

I have two truss clamp positions on my RGB that I use where possible, but also use a tripod when it's the best option (bearing in mind what Steve said about vibration and movement; I would only use the tripod on a solid concrete stage).

I think Carl B uses the mounting method that you described but I have installed the top hat mount in to the chassis of the projector, and from memory your toblerone has an extremely solid frame so maybe that's an option?

Cheers Ian,
I know you're fairly knowledgeable in that sort of area, so could you suggest a decent tripod if the ones I suggested are naff...?

You're right, I could mount a top hat to the base of it.
If I did, I'd probably make it removable, or use some sort of quick release with it, as I know I wouldn't want it on all the time.
I'd also have to find the centre of gravity of the thing first though

Ta,
Dan

[smokeAndMirrors]

Not quite. A fan has higher energy density AT THE VERY ENDS OF THE FAN when compared to all other scanned patterns, since at the ends of the fan the mirror has to make a 180 degree turn, which is (obviously) the largest turn it can make, thus you have the highest "dwell" time on a single point while the mirror reverses it's velocity. But the center of the fan has the same energy density as any other scanned image. (You'll also notice that the performer is not standing at the edge of the fan in that picture.)

But really, all this is irrelevant. Even at the ends of the fan, the power density is nowhere near as high as you would have with a static beam. So long as the beam is scanning at a reasonably fast rate (30Kpps, let's assume), the fan is many orders of magnitude safer than the static beam - even at the ends of the fan.

Adam

Gotcha. Though my point was that the average energy density over a fan of length L would be notionally E/L whereas for a tunnel of diameter L would be E/(pi*L) where E is proportional to the energy in a static beam. And whilst these are crude calculations, LaserSafe shows a safer rating for a tunnel or triangle than a fan, all other parameters equal.

[smokeAndMirrors]

Meanwhile, back on the OP, I have seen this:

http://www.htfr.com/more-info/MR264746

which would fit nicely onto a tripod and hold the laser from the top.

[buffo]

It depends on what you mean by "all things equal"... If you're saying that the width of the two patterns is the variable that is held equal, then yes, the tunnel is safer, but that's only because the linear distance around a tunnel is a lot longer than the diameter of the tunnel. The laser is tracing over a longer "line", thus the average power along that line is lower.

However, if you instead compare the circumference of the tunnel with the width of the fan, your calculation yields the same energy density. (Which, as we've already discussed, ignores the fact that there will be slight "hot spots" at the ends of the fan, which you obviously won't have with a continuously-scanned tunnel.)

The difficulty in calculating the MPE for a scanned effect like this is the main reason why ILDA is suggesting a simpler approach, detailed here. It requires only a single measurement of a static beam at the closest point of audience approach.

Adam

[smokeAndMirrors]

The difficulty in calculating the MPE for a scanned effect like this is the main reason why ILDA is suggesting a simpler approach, detailed here. It requires only a single measurement of a static beam at the closest point of audience approach.

Cheers buffo, that's an interesting read. Can't find the details about the Laser MPE meters easily, though. Hitchin is just down the road, too. I bet they cost scary amounts.