Perceived brightness 12watt vs 3 watt

[flecom]

safely use something like that in a room I'd have doubts off... the scatter of that is very hazardous to just look at... so indoors it still depends.. also reflective materials at any upper level will be a REALLY big issue. Would be careful saying that overhead is that safe automatically.

again, if you know what you are doing you can do just about anything safely

scatter isn't as bad as you might think, but again, you should be able to do the calculations and determine that

[norty303]

I've seen laserscopes used indoors in the UK quite safely. Brixton Academy is one example

[Sandstorm]

Sorry for long post in advance.
Please guys, everything is completely calculable and I see here lots of 'I feel this laser to be brighter than another one' in the powers and divergences field. Stop this witch-hunt
So, going to write down some things which you all probably already know (and probably it is floating somewhere in the forum already), but maybe that will help someone.

This divergence vs power thing has wrong approach in most cases. We do not see power, nor the divergence. The parameter which gives visibility of the beam is power density - it's simply power divided by the area of the beam. The area of the beam is mainly determined by the beam waist at the aperture and divergence. Since we usually have divergence in mrad it approx. shows the number of mm added to the waist over the travel distance of 1m, i.e. if we have 1.1x0.5mrad divergence on 4x4mm beam, @ distance 10m we should expect beam to be 15x9mm (4+10*1.1 x 4+0.5*0.5 mm).

Once we clear with that, there are a few cases to consider:
1) Top hat beams. If we have multimode source with more or less uniform intensity over cross section of the beam, we can calculate the power density = Power/(width_x*width_y). Saying that beam becomes 4 times denser if the divergence is 2times lower is too abstract, because in LD case we usually have fast and slow axis with different divergences and usually 'lowering divergence' is understood as correcting FA... which relates to linear power density dependence. If the collimation lens is changed which results in lower divergence it changes both axes, so the power density changes in square dependence.
2) TEM00 beams. If we have singlemode source the intensity cross-section of the beam is Gaussian. In this case it's hard to determine what actually is the 'beam visibility', however it's usual to calculate peak power density. Here how it's done:
We take power density at FWHM as PD=Power/area(FWHM)=Power/(pi*d/2(FWHM)). Since power density is always linear dependent on power, the peak power density is now 2x PD(FWHM). For the sake of simplicity there is a formula for mm units derived, as it's the most common beam waist diapason: PD(max)=250/d[mm]*Power[W], which has the result in units [W/cm^2]. you have probably seen it in your laser safety course for calculating MPE (haven't attended course myself, but they definitely should talk about it).

So now you should start to see the pattern. To sum up:
If we take multimode LD and increase it's power 2 times, power density increases two times.
If we correct multimode LD FA to make FA divergence 2times lower, PD increases two times.
If we change colli lens of the same LD to make SA and FA divergence 2 times lower, PD increases 4 times.
If we change the source from multi to single mode with the same divergence, aperture waist and power, not only the area of the beam changes (from square to circle, which gives an increase in density 1.27 times), but maxPD increases 2 times because of Gaussian profile of the beam itself.

If we try to determine what specs laser is best (in this case it's 'which rocks best' or 'which should give biggest 'wow''), we simply have to calculate power density in the distance at which we're usually working. For smaller venues you'll find the power contribute more, for big outdoor shows divergence gets its toll, however you can actually calculate it and not simply 'feel' one beam being brighter than another one.

Hope that helps.

[Bradfo69]

considering the OP is in the US I doubt he will be doing any audience scanning so eye safety really isn't a concern

Certainly not with anything I have now. It's a goal for 2015 though and working with X-Laser for a Polaris system.

you could safely use a 40W laserscope inside a room if you know what you are doing (not that anyone should mind you, but you could) but you keep safe margins, make sure nobody can access "no go" areas and make sure wherever your beams are terminating you don't have a risk of causing a fire etc

I think I've seen some of Jon's pictures running a scope indoors and doing the ILDA test pattern.

anyway brad I don't know if you remember the outdoor show but when we had Jons big (think it was 12w?) RGB next to my 6W RGB it looked SIGNIFICANTLY brighter, and he had gigantic beams

Yes, as mentioned earlier in the thread, his is a 9 watt and being an RGBLasersystem Compact, I'm sure it had excellent beam quality. (Not saying yours has worse beam quality) which contributed to that. I know in the auditorium at SELEM, yours was always brighter than anything else in there for the past several years.

[Bradfo69]

Very interesting. Thanks for taking the time to type all that up. I need to re-read it later to thoroughly digest it all since I just woke up and have to run out the door to work.

Sorry for long post in advance.
Please guys, everything is completely calculable and I see here lots of 'I feel this laser to be brighter than another one' in the powers and divergences field. Stop this witch-hunt
So, going to write down some things which you all probably already know (and probably it is floating somewhere in the forum already), but maybe that will help someone.

This divergence vs power thing has wrong approach in most cases. We do not see power, nor the divergence. The parameter which gives visibility of the beam is power density - it's simply power divided by the area of the beam. The area of the beam is mainly determined by the beam waist at the aperture and divergence. Since we usually have divergence in mrad it approx. shows the number of mm added to the waist over the travel distance of 1m, i.e. if we have 1.1x0.5mrad divergence on 4x4mm beam, @ distance 10m we should expect beam to be 15x9mm (4+10*1.1 x 4+0.5*0.5 mm).

Once we clear with that, there are a few cases to consider:
1) Top hat beams. If we have multimode source with more or less uniform intensity over cross section of the beam, we can calculate the power density = Power/(width_x*width_y). Saying that beam becomes 4 times denser if the divergence is 2times lower is too abstract, because in LD case we usually have fast and slow axis with different divergences and usually 'lowering divergence' is understood as correcting FA... which relates to linear power density dependence. If the collimation lens is changed which results in lower divergence it changes both axes, so the power density changes in square dependence.
2) TEM00 beams. If we have singlemode source the intensity cross-section of the beam is Gaussian. In this case it's hard to determine what actually is the 'beam visibility', however it's usual to calculate peak power density. Here how it's done:
We take power density at FWHM as PD=Power/area(FWHM)=Power/(pi*d/2(FWHM)). Since power density is always linear dependent on power, the peak power density is now 2x PD(FWHM). For the sake of simplicity there is a formula for mm units derived, as it's the most common beam waist diapason: PD(max)=250/d[mm]*Power[W], which has the result in units [W/cm^2]. you have probably seen it in your laser safety course for calculating MPE (haven't attended course myself, but they definitely should talk about it).

So now you should start to see the pattern. To sum up:
If we take multimode LD and increase it's power 2 times, power density increases two times.
If we correct multimode LD FA to make FA divergence 2times lower, PD increases two times.
If we change colli lens of the same LD to make SA and FA divergence 2 times lower, PD increases 4 times.
If we change the source from multi to single mode with the same divergence, aperture waist and power, not only the area of the beam changes (from square to circle, which gives an increase in density 1.27 times), but maxPD increases 2 times because of Gaussian profile of the beam itself.

If we try to determine what specs laser is best (in this case it's 'which rocks best' or 'which should give biggest 'wow''), we simply have to calculate power density in the distance at which we're usually working. For smaller venues you'll find the power contribute more, for big outdoor shows divergence gets its toll, however you can actually calculate it and not simply 'feel' one beam being brighter than another one.

Hope that helps.

[m0f]

There are factors other than power density that would be hard to calculate. For example in experimenting with the safety scan lenses which increase divergence, even for overhead shows, I have in some cases found some gain in perceived brightness of simple beam effects by increasing the divergence, complex beam and liquid sky type effects however seem to benefit more from increased power density.

For simpler beam effects I think above a certain density, the eyes can't discern the difference in power level as much as a larger beam area can increase the amount atmosphere it's interacting with. Of course it's relative and down to personal taste. And with more complex beam effects and liquid effects, power density becomes a big factor due to increased persistence of vision from a denser beam.

[norty303]

Sorry for long post in advance.
Please guys, everything is completely calculable and I see here lots of 'I feel this laser to be brighter than another one' in the powers and divergences field. Stop this witch-hunt
So, going to write down some things which you all probably already know (and probably it is floating somewhere in the forum already), but maybe that will help someone.

This divergence vs power thing has wrong approach in most cases. We do not see power, nor the divergence. The parameter which gives visibility of the beam is power density - it's simply power divided by the area of the beam. The area of the beam is mainly determined by the beam waist at the aperture and divergence. Since we usually have divergence in mrad it approx. shows the number of mm added to the waist over the travel distance of 1m, i.e. if we have 1.1x0.5mrad divergence on 4x4mm beam, @ distance 10m we should expect beam to be 15x9mm (4+10*1.1 x 4+0.5*0.5 mm).

<snip>

Hope that helps.

So, in summary...

Its not about divergence, but as divergence is a property of power density, it is about divergence??

[Sandstorm]

So, in summary...

Its not about divergence, but as divergence is a property of power density, it is about divergence??

No, It's about power density, which consist of both - power and divergence (+aperture width, but in long distances it might be neglected). I'm just saying that there is no such fight - divergence vs power - they both contribute to the same thing and everyone might make numerically argumented choice of the way to go considering the show types they want/(have a demand) to perform.

[flecom]

lets just all agree more is better?

[edison]

So less power but lower divergence gives equal brightness and better graphics versus higher power and higher divergence.
The low end market is willing to pay more for more power with a higher divergence since the eventmanagers demanding this but in reallity it doesn,t contribute to make its brighter and the overal looks is worse since the beams are not sharp but a bit blurry.

So the choice is spending money on lower power with low divergence with good graphics versus higher power with same brightness and worse graphics.

Take your pick

Oh did i mention we do red 1 watt in 0.6mrd ?: