Ideal RGB Balance

[soforene]

Is there a definitive statement regarding the ideal power of each of the three lasers in a projector to provide the perfect balance?

e.g.
R - 300mw
G - 200mw
B - 100mw

[carmangary]

A rule of thumb is you need 2x blue as your green and 4x red as your green: 1:2:4 R:G:B.

But, that is still meaningless because it doesn't take into account optics losses within your scanner. For example, my lasers are Green 50mw, Blue 70mw, and Red 185mw and the balance is perfect. But, if you measure the laser power at the exit of the galvo mirrors those powers will be completely different. I am not sure what they are. And, it really doesn't matter because each system will be different (unless built the same).

[soforene]

Cheers for that. I was just wondering about rough ratios so, using your ratio, in my example, the rough mix to achieve good colour balance would be;
R - 350
G - 100
B - 150

Looks like the Bluey would be the most expensive laser in that equation (or in any combination, come to think of it).

[allthatwhichis]

Hey man, do a lil searching and you will find buffo has posted anough posts on this to beat it in the ground. He has broken it down to different wavelengths and others have thrown a few charts that show ratios very well. Best thing to do is experiment and find what you see as a good balance.

[soforene]

Thanks but errrr it wasn't for me.
It was for a friend.

I have looked about and found some useful posts such as this, this and even this.
Although that last one goes a bit OTT in terms of charts and graphs for my meagre comprehension (and what the hell would I be doing in the "Advanced Technical Discussion" section anyhoo !?!)

The level of technical expertise on this forum is phenomenal but I am way back down the line almost at the starting point and hence, data presented in simple terms is much more accessible for me.
Forgive my "noobness".

I guess you could chalk this thread down to another potential Wiki entry (Projectors for beginners).

Tread softly, you laser gods, mere mortals also walk amongst you......

p.s. This link is a cracker !!

[godfrey]

I asked Bill Benner this very same question on the Pangolin forum back in September of 2006 - here is his response...

The exact ratio depends on a number of factors, including the wavelength of the lasers used.

Many people incorrectly look at the CIE Chromaticity diagram and try to deduce the correct ratio of colors using only that as a reference. But the CIE Chromaticity diagram does not provide the full picture with laser light because it does not account for the effects of Forward Scattering and Raleigh Scattering which tends to give shorter wavelength lasers a boost (i.e. blue lasers appear brighter than the diagram says that they should). I have seen RGB laser systems with a surprisingly low amount of blue power, and using a surprisingly short blue wavelength, give a surprisingly white appearance!

Also, as counter-intuitive as it seems, 650nm or even 671nm red lasers are not half as bright or one-third as bright, as the CIE Chromaticity diagram would suggest. The rules for laser are a little different than this one table taken out of context suggests. Having worked with 635, 650 and 671nm lasers, I personally would rather have the nice beam profile and similar bandwidth and on/off behavior that a 671nm laser provides, than the large, crappy beam profile and inconsistent (with DPSS lasers) on/off characteristics of a 635nm laser (especially for graphics applications).

In your case (and in most cases with commercial RGB lasers) the bigger question will be price and availability. When looking for lasers in the marketplace, chances are the green laser will always be the cheaper of the three anyway, and also coincidentally provide more power than you need. Similarly, 671nm red lasers are usually more available, at higher power levels and a lower price than 653nm lasers. For this reason, more often than not, RGB laser systems are not perfectly color-balanced, and software (such as Pangolin's LD2000 series) can reduce the amount of green for laser graphics applications, but still easily provide the full power of the laser when desired for beam applications. For beam applications, often, the degree of "white-ness" is of less importance than raw power.

So, instead of trying to figure out precisely how much of which wavelength you need, I would first start with budget and availability, and work from there...

Yes, I put the "quote Laser God" stuff in, just incase you're wondering....



Phil

[mliptack]

Haha - Allthat I was thinking the same thing. When I read the subject of this post my first thought was 'oh no - I dont want to have to let Adam take this one again!'

To sum it all up - there is no PERFECT WHITE BALANCE! its subjective!

BUT there are a few guidelines that Adam has so eloquently stated many times in the past that take into account the wavelength of the red laser you are using. I dont believe he has factored in using a 457nm laser for blue yet, but you would need more power than a 473nm thats for sure (since it is moving away from the eyes most sensitive range).

[buffo]

Haha - Allthat I was thinking the same thing. When I read the subject of this post my first thought was 'oh no - I dont want to have to let Adam take this one again!'

Blow me!

Seriously though - I've done my best to stay out of this one, despite the baiting from both you and Allthat! There is more than enough discussion on the topic in the forums as it is. Besides, I didn't want Dr. Laser to drag out the dead horse smiley again.

(Soforene, if you want more info, just search for "Color Balance" and you'll get more than you ever wanted.)

And for what it's worth, I agree 100% with Bill's suggestion to start with a budget and go from there.

As for 457 nm blue - when I can afford one I'll look into the numbers for color balance. But I don't see that happening for quite some time.

Adam

[soforene]

...if you want more info, just search for "Color Balance" and you'll get more than you ever wanted....

Already done that after a gentle botty smacking from allthat.

Although we who speak the Queens English use the corrrect spelling of "colour".

[godfrey]

As for 457 nm blue - when I can afford one I'll look into the numbers for color balance. But I don't see that happening for quite some time.

Adam

A 1 watt 457nm 10kHz analog modulated / 10% stability only costs $17,008.74

I'm sure a group buy could get it down a few dollars...literally - just a few dollars.


New fishing boat or a 1 watt laser? Yeah, I thought so.