Green lines are fascinating

[absolom7691]

I had some free time today to mess around with the old and the new and something in between. I did a side by side by side comparison of all of my green lasers. What I found fascinating was that between my 543nm and 532nm, I could see a difference in the color but it was barely noticeable. In fact, the only way I could really detect a color difference was by making my eyes unfocus, causing a blurry halo. Only then could I really detect a difference in color. This is obviously only a difference of 11nm. What I found the most fascinating is that between my 532nm and 520nm, a 12nm difference, the color variation was staggering. I haven't really looked at color charts but this would lead me to believe that "true green" is, without a doubt, 532nm. Even at 543nm, my HeNe didn't really look yellow but 520nm looks more "blueish". While I am intrigued by the color of 520nm green and will be using it in my single mode projector, I still like 532nm as the green leg in RGB setups and this little comparison showed me that.

My phone is not a suitable camera for this subject. When I get more time, I'll get my Canon out and snap a few decent pics and may use a few lenses to expand the beams. The 3rd pic seems to show the best color rendition but only if you view the pic at full resolution.

Reading from Left to Right: 520nm, 532nm and 543nm...

[SoulFeast]

I notice the same thing. However, the green to blue spectrum (cyan?) is a very small portion. Similar to the yellow/orange spectrum. I can tell the 501 line from my 496 line like it's day or night. That's when tuning through, so no side-by-side comparison.

[The_Doctor]

Since I hacked my Lambdapro soft start circuits to put power control there, I tested one against the green HeNe that Jem sold me. Very similar beam specs, which is interesting, and useful. If anythign Lambdapro DPSS wins, with the lower power DPSS's, UG type.

As to colour, I see the difference easily, once I match brightness, but not if I don't. 532 is very green, a kind of pure green for me, if very slightly bluish, but context is everything, it can look yellowish in daylit contexts. HeNe green is much more like a sunlit leaf. I like it better than 532, and it pairs very well with HeNe's red too. Very 'natural' colours. I'm put off the Osram diodes the moment someone said 'traffic lights'. That colour is intended to avoid colour-blindness problems, but to me it looks very blue. Which is vaguely interesting because some have said that argon 488 looks very cyan, but not to me, I find it a good quality blue, though I prefer deeper...

[absolom7691]

I agree, I like the color of 520 but I am also put off by it. I would say the 520s are a little more "green" than a traffic light but definitely leaning toward the cyan side of the green spectrum. I think 532 is a fantastic green and 543 would be a great green line for RGB but I am not too keen on 520 to take the job of green. When I get home, I am going to take more pics with my SLR. I am going to try some lenses to expand the spot sizes and also shoot some pics in the fog. I just wish my GreeNe put out more than 1mW.

I would also say that 488 is not cyan. It is more of a ligth blue, no hints of green at all. My favorite blue lines are 457 or 473 too bad they can only be had in DPSS or OPSL (460nm?). I am still really put off by 445~450.

[SoulFeast]

488 is weird to me... If I go from 514 to 488, it's all blue, but the other way around, or with a 473 or 450 on, it looks blue-green. Very strange..

[The_Doctor]

Well, you've heard of that thing where some prof wore coloured glasses for a week, then found the world looked like its inverse for a while after he stopped? This is the problem. There's context, expectation, all sorts of intangibles to confuse, AND the adjustments of brightness just add to the merriment. It goes further... I shone a diode red (about 655 nm I think) down the corridor with the green HeNe, and found that the diode's red failed to light the hallway at 50mW the way 2mW of green can do it, but the ambient light down there was orange when they mixed. So perception of colour and intensity seems to depend on the spread of light too. I suspect there is not, and may never be, a definitive map of all these possibilities. Variations on human colour perception alone pretty much kill that notion. So ultimately we need tunable lasers with manual intensity scaling, and to make artistic judgements on the spot, in context, same as stage lighting has to do it. What I hope, but am not sure of, is that if we choose deeper blues and reds, and use a mix map to add in tiny amounts of green, we might simulate the blues and reds that are closer to green. Old idea for sure, but I never saw any consensus on how well it works.

[absolom7691]

488 is weird to me... If I go from 514 to 488, it's all blue, but the other way around, or with a 473 or 450 on, it looks blue-green. Very strange..

What's interesting about this too, and goes along with the "context" that Crow is talking about... I had an argon way back in the day and my green came from it. It was 514nm green which looked good back then. Now, I think it is too close to cyan but that is only because I have been running 532 for the last 8 years. The other bit too is how, when comparing lines of color, blues and greens affect eachother as far as my vision goes. If I were looking at my 520 next to my 473, I am sure it would look super green. I need to look at this more. I am finding all of it very interesting.

[The_Doctor]

Dayglo. Punk posters and Rave flyers... That's what argon green is for me. I like it, and I can imagine three kinds of RGB mix, one that aims for that lurid un-natural but exciting look, which would include the Argon colours, another that aims for 'natural', using HeNe green (not that I know how to get a lot of that) and 635, and a deep sky blue, likely 473 might do it, and the third would aim for strong vivid deep colour, so 532, 660, 445, or maybe closer to 460. (Which is where I was hoping that a bit of green might make the others emulate the reds and blues from the other sets). I've never had enough lasers to test this much. What I do think is worth having is a box of LED's. Strong bright ones. They can help gauge colour a lot better than looking at printed paper, and are cheap and small enough to try in contexts where quick changes with lasers are impractical. They also come in many narrowband colours these days.

[discothefunkyhippo]

What's interesting about this too, and goes along with the "context" that Crow is talking about... I had an argon way back in the day and my green came from it. It was 514nm green which looked good back then. Now, I think it is too close to cyan but that is only because I have been running 532 for the last 8 years. The other bit too is how, when comparing lines of color, blues and greens affect eachother as far as my vision goes. If I were looking at my 520 next to my 473, I am sure it would look super green. I need to look at this more. I am finding all of it very interesting.

I read a few papers while I was in school on this very subject. Some studies also "found" that if the word of a color was written or printed below the color it would affect how the viewer perceived it, especially with those "in between" colors... I can probably dig up those papers if anyone is interested.

[mixedgas]

It gets more fun when you toss in Mesopic, photopic, and scotopic vision.

One demo we did at Selem by my request was 488 and 576 make a cool blue white when mixed. Add a little of a green line and the apparent color shifts red when dark adapted.

The 576 krypton line is yellow green to me. The 575 kr line is actually yellow. 532 is lime green to me. 514 is actually light green to me.

I have good reason to believe there are genetic differences in color vision besides color blindness.

Steve