Safe bright green fatbeam w/TTL recommendation for writing on buildings

[maxcady]

hi everyone, if this is posted in the wrong section please let me know. i'm new to PL.

I've been doing some written words projected across buildings with my homemade XY galvo system. it comes out looking good in photographs, but to the naked eye its not that stunning. i've been using a red fatbeam laser and its just barely visible, with the ambient night street lighting. my green fatbeam laser seems like it would be very bright and eye catching, but it does not have TTL control, which means my words wont look their best.

if someone could recommend a green laser with TTL that would be good for writing on buildings outside at night i'd appreciate it. ill need the laser for a public event on the 23rd, so i need to purchase something soon

i'd prefer if it was safe for the eyes if it did happen to hit anybody, my current green laser is safe and its a fat beam which makes it double safe as i've understood. i'm sorry i dont know the spec of my green fatbeam, i'm still new with this side of the laser universe even though i've been doing XY shows for years. the green fatbeam was provided for me by someone else and i was told it was safe and that the beam was larger than the pupil of your eye so if it did hit, it still would not be the full energy of the laser.

i figure since the word will be using TTL there is no way the laser could really hurt anyone

thanks

[JStewart]

If you don't know the specification of the green beam, how do you know it's safe?

Just because a beam has larger diameter beam than a human pupil does not automatically make is safe unfortunately. For the light that can still get through the 7mm pupil aperture can still be more than is safe to have on an eye. If you are using lasers to project onto a building outdoors, to be effectively visible, they will likely be in excess of what is safe to view directly.

Also, how does TTL prevent a laser from really hurting people?

James

[planters]

Rest assured that you will receive a lot of critical comments about your plans. An outdoor projection at an event (people are expected) onto a building that will potentially have multiple surfaces with various angles and percentages of reflection with a laser of unknown power and a homemade galvo system is pretty "out there".

You should absolutely prefer not to hurt anyone, but your approach is awfully loose. A fat-beam laser has little importance without knowing the divergence(or convergence) and power. TTL has nothing and I mean nothing to do with the laser's ability to hurt someone. This just means it CAN be modulated up or down not that it will be as it sweeps across someone's field of vision.

You are not unique in your interest or what you are trying to do. There are a lot of powerful laser pointers out there being used recklessly and in some cases even maliciously. However, you are here now on this forum where lasers are discussed by both newcomers and by very experienced operators and engineers. You can receive enormous amounts of free help and guidance. This can keep you safe, out of trouble and enable you to quickly acquire powerful lasers, hardware and fantastic ways to use them. But, your plans for the building are a bad idea.

[mixedgas]

My scanning laser safety notes are at home. I will try to get to you tomorrow with some basic math.



Lets assume you are trying for an intrinsically safe display, which seems to be your in intent? I'm looking at two of your posts on this topic..
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Is there any way I can get you to scan with your lowest beam a minimum of three meters up on a wall and conform with international norms? At least till you get some more experience and some test gear... Avoiding exposure by ensuring the audience is a safe distance away is the best means of securing safety in many cases.
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If your placing the beam low, then you want to be "Eye Safe" which opens the following "Can of Worms:
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One of the problems of going FAT beam is it decreases the image's intrinsic brightness, and only a few logos look good with a fat brushstroke.
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The second problem is with any given laser, especially DPSS, is you cannot assume you know what the laser's power and beam shape is, especially with low cost Chinese green lasers that do not have good thermal compensation. I've seen "100" mW lasers ship at 250-300 mW. I've also seen Chinese lasers ship with a M Squared (Measure of total beam quality plus divergence) of 1.3 (excellent, nearly perfect, narrow, low divergence beam) when their spec sheet calls for a 3 or 4 (Horrible mode profile, very high divergence.) There just is too much randomness in the low cost green products to make any assumptions. My experience with low cost lasers is there are lies, damned lies, and low cost laser quality control test sheets. :-)
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On a quality laser diode, you have a very good chance of a 150 mW rated diode doing nearly 150 mw with say + 20% /- 10 % error if conditions match the factory test. But still that is not a good enough measurement for audience scanning, you really want to know +/- 2.5 % what your doing. That takes a well made, NIST traceable, laser power meter.
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The third problem is that lasers drift, your quality control procedure that ensures you are safe, must be an ongoing preshow task on a nightly basis. With a logbook, at least in the states.
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So at minimum you need a reasonably fast photodiode and oscilloscope if you don't know your precise scan rate in software, an accurate laser power meter, and a way to approximate your beam divergence. Then you need to evaluate each effect.
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I'm sure the 10x MPE fans will chime in shortly with their "simplified" easy math and lens procedure. However, most of them will concede that you should still be able to make good measurements and know the basics of audience scanning math COLD before you do it. Including the fact that laser exposure is cumulative.
~
We'll leave the whole "You need a CDRH Varience/ Arizona, New York, Texas License, /UK Health and Safety some sort of insurance" thing for another day, its been beat to death...
However if your beam crosses an eyeball, you damn sure should have insurance, or consider the fact that if your unsuspecting audience member is a heart surgeon/pilot/lawyer and makes 230K$ a year, your on the hook for the rest of your life in the US if you expose them to eye damage. Your probably far worse off if they are gang member or a member of the Mafia and they start seeing black spots.
~
And if you do not have much in the way of finances, consider that going down this route the right way is initially expensive, and even at 10X Maximum Permissible Exposure, the effects can be wussy... Especially if there is metal halide lighting or LED walls where your doing your effects... Following the three meter rule eliminates all the rigorous work listed above.


~
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The above mess is why I'd encourage you to produce your effects three meters up and two meters horizontal from any audience accessible point. Which drastically reduces the engineering constraints on what you want to do... You can have much more brightness, a much lower divergence, and unlimited scanning speed. The cost for the effect is far less, and you can invest that money into a better laser, and advertising to increase your business.... Use of a simple metal mask to make sure the light only goes where you want it costs far less then engineering a "FAT " beam.
~Steve
ILDA Certified LASER SAFETY OFFICER.

[planters]

Steve,

Your advise is good and useful, but let's step back and remember that the OP states that he want's to place a logo on a building and does not even seem to have access to a power meter. The surface of the building is unknown and may be highly specular. If these galvos let loose the metal mask is a very good idea, but will he know to block the failed beam if it hits the mask?

I agree that if we make this so difficult he is likely to drift away and try something stupid. That is why I agree with you on the CDRH stuff and I would be wary of solutions that require a big investment.

maxcady,

Can you link some video or images of your set up? You said that you have been doing X Y shows. Can you post some of what you have done? Where are you located? This is not to track you down; you'll do what you want, we know, but there may be someone close that can jump start your system. Do you have a power meter? They do not have to be expensive and we can show you how to find one if you don't.

[maxcady]

If you don't know the specification of the green beam, how do you know it's safe?

i have it written down somewhere, it was provided for me by someone helping me to build laser systems. i have a green, and a red, both fatbeams, both safe for the eyes. i have a blue fatbeam which is not safe for the eyes under any conditions. this is what i was told, i dont have the specs on me right now but i can get them and post them here.

Just because a beam has larger diameter beam than a human pupil does not automatically make is safe unfortunately. For the light that can still get through the 7mm pupil aperture can still be more than is safe to have on an eye.

I understand. However I guess I should have specified that with these lasers in particular, I have been told that the laser intensity is ok and then in addition to that, its a fatbeam which further disperses the beam and makes them safe. Or are you saying that under no conditions does a fatbeam lens spread the light out to make any difference at all ?

If you are using lasers to project onto a building outdoors, to be effectively visible, they will likely be in excess of what is safe to view directly.

I'm fairly certain that my green will be above the minimum requirement of just being able to be seen, and be a bit "eye-catching" or "stunning" if you are standing on the street and happen to see it. I haven't tried this yet, but my red laser is much dimmer than my green and it was reaching the minimum level of intensity when i did it on location out in the city. I'm sorry I don't have the specs, I'll post them here, and when i look at them, I'll mark the laser units directly so that I don't forget..

Like I said before, I've been doing stuff with lasers for years and have been quite involved but it's mostly on the artistic side, just now getting involved in the other side of the laser universe so there's things I forget, i got it all written down though and i'm trying to do it all properly and safely, i appreciate all the help on here!

Also, how does TTL prevent a laser from really hurting people?

I guess it doesn't necessarily, but in the case of the specific blue laser that was provided to me, I have been told that if I'm using TTL, the rapid blinking would make the laser safe enough that if it happened to cross someones eyes during an XY modulation laser show it would be the same as if the green fatbeam of mine crossed someones eyes briefly, it would be ok. If my blue laser is full blast with no TTL and it crosses someones eyes i've been told that it could be dangerous.

Now that I've clarified a bit more, am I still incorrect about anything? I'll get the specs of my lasers posted here soon, sorry about that.

I see a lot of green TTL lasers on amazon that look great, i was just looking for a recommendation for one that wouldnt break after a month of use, or one that is better built in some way, maybe has a quieter fan, or actually meets the specs that are listed, or any other snafu's that I could fall into by just buying one that looks good to me. I've always had the lasers provided for me by a builder, so I'm not sure where to source them from when I'm doing something on my own..

[swamidog]

i have it written down somewhere, it was provided for me by someone helping me to build laser systems.

I guess it doesn't necessarily, but in the case of the specific blue laser that was provided to me, I have been told that if I'm using TTL, the rapid blinking would make the laser safe enough that if it happened to cross someones eyes during an XY modulation laser show it would be the same as if the green fatbeam of mine crossed someones eyes briefly, it would be ok. If my blue laser is full blast with no TTL and it crosses someones eyes i've been told that it could be dangerous.

these statements make me very concerned about the credibility of advice you've been given in the past.

without knowing the laser power and divergence / spot size, it's impossible to say if these lasers are eye safe.

[maxcady]

Rest assured that you will receive a lot of critical comments about your plans. An outdoor projection at an event (people are expected) onto a building that will potentially have multiple surfaces with various angles and percentages of reflection with a laser of unknown power and a homemade galvo system is pretty "out there".

You should absolutely prefer not to hurt anyone, but your approach is awfully loose. A fat-beam laser has little importance without knowing the divergence(or convergence) and power. TTL has nothing and I mean nothing to do with the laser's ability to hurt someone. This just means it CAN be modulated up or down not that it will be as it sweeps across someone's field of vision.

You are not unique in your interest or what you are trying to do. There are a lot of powerful laser pointers out there being used recklessly and in some cases even maliciously. However, you are here now on this forum where lasers are discussed by both newcomers and by very experienced operators and engineers. You can receive enormous amounts of free help and guidance. This can keep you safe, out of trouble and enable you to quickly acquire powerful lasers, hardware and fantastic ways to use them. But, your plans for the building are a bad idea.

Hi planters, thanks for writing this. Allow me to clarify a bit, and perhaps you will then say that what I'm doing is not such a "bad idea." ?

I'm not simply buying lasers on ebay and amazon and turning them on at events. I'm sorry if that's the impression my post gave.

I've been doing XY laser shows for years at events and parties with people present, as well as produced music videos using the same lasers on the talent and aimed directly into the camera sensor. I work with an engineer/builder who helps me achieve my 'out there' ideas safely, and with gear that will work with the way that i prefer to work (without computers: voltage from analog synths/computer playback of analog synth improvisations thru expert sleepers es-3/es-6 combo, and often filming it, or syncing the laser to the camera shutter [or tastefully out of sync])

The laser and galvo system that I've been using on buildings was originally designed to be used on the talent performing on camera, its totally safe. It's my "party system" that I can bring to a crowded dance space and just turn on and not worry about anything.

However on buildings its just slightly too dim, so i'm looking to upgrade the laser inside it. I really think there has got to be a middle ground where the laser is totally cool for people, and still visible when projected big. I have a green fat beam thats been provided for me by my team for this party laser system and its safe for talent, its definitely bright enough for a building, but it has no TTL control, so I'm looking for a new green laser to use for these purposes.

When I mentioned TTL before, it would be looping a line of text, so I figured it would be constantly blinking, because the text is not static, but mixed with white noise and some bitcrushed voltages that I'm crossfading around using a joystick, so the word is a big blinking mess that now and then congeals into itself and lets you read it and then it disintegrates again, its being gated and modulated like crazy and it's never static.

So what do you think now that I've provided a bit more details, do you still think this is a horrible idea? I've been doing it and even when the police come up to me they are just interested in the system and they dont tell me to stop. It seems good to me..

[maxcady]

these statements make me very concerned about the credibility of advice you've been given in the past.

without knowing the laser power and divergence / spot size, it's impossible to say if these lasers are eye safe.

Why do these statements make you question the people I have providing the laser builds for me?
Is it because under no circumstances would this be true, no matter what the specs of the lasers turn out to be?

I'll get the specs for you. Thanks for writing!

EDIT: i'm not coming at you in an agressive or defensive way at all, but thats how the first sentence of this post looks after i read it...

[swamidog]

Why do these statements make you question the people I have providing the laser builds for me? Is it because under no circumstances would this be true, no matter what the specs of the lasers turn out to be?

I'll get the specs for you. Thanks for writing!

it... might be true.

but there's just not enough information being provided to make sure and since there's potential for eye damage, it's worth double and triple checking.

TTL is not inherently safer than analogue modulation. with TTL, the beam is either full on or full off. with analogue modulation, the beam can be full on, full off, or any power level in between.