What's the wavelength of pure green?

zyxwv99 said:

:wave:It looks like the HEX convertor may have been right about green after all: 510nm.

I had seen that number before in various studies, but couldn’t wrap my brain around it. It conflicted with my own experience of 532nm lasers, and with what others here were seeing. However, I forgot to take into account how color vision studies are usually done: with monochrometers.

Photopic (color vision) covers about 9 orders of magnitude of brightness. The bottom 2 overlap with scotopic (night) vision. The area of overlap is called mesopic (twilight) vision. In that region our color vision is comprmised. The 2 top levels have problems with glare, flashblindness, and the M-channel (green) getting overloaded. So that leaves about 5 good levels in between. In typical color-vision studies, before people look into the monochrometer their eyes are dark adapted for 10 minutes. Then they get something like 27 trolands (with a 2 mm artificial pupil). In other words, at the bottom of our 5 good levels of color perception.

To find out which wavelength is the most green, they show people a bunch of wavelengths at 10nm intervals, presented in random order, and with brightness automatically adjusted for each wavelength so they look equally bright. Then they have them answer questions, starting with “How red was it?” They have to answer on a scale of 0% to 100% in increments of 10%. Then the same thing for green, blue, and yellow. The test subjects have to make sure the percentages add up to 100%. Then one last question: how saturated was it? The results for each wavelength are then weighted according to the perceived saturation level.

When the results are plotted on a graph, the blue and yellow curves hit zero at the same point where the green curve is highest. That wavelength is then called “unique green” because green is the only color reported as being seen at that wavelength.

So then I looked at the data on Bezold-Brucke shift. It turns out that Bezold-Brucke only apples to colors seen simultaneously (or near-simultaneously). Otherwise there’s a similar phenomenon called “no-contrast hue shift.” I think that’s what going on here. In either case, 532nm, if it were bright enough, could easily shift to the equivalent of 510nm.

Now I’m trying to figure out how bright our laser dots are. If you have the specs on the laser (including wavelength, beam diameter and spread in mrad) it’s not too hard to calculate the brightness of the dot at a particular distance. However, I’m not sure how to convert that to perceived brightness in terms of lux or trolands.

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trencheel303 said:

This entirely depends on how you define green. Similar to how I describe what a lot of people see as yellow to be orange (i.e., SOX lighting to me looks positively orange), I suspect a lot of what people call "true green" is actually what I see as turquoise/teal/cyan.

I admit I've never seen a 520/515/510nm laser in person, but judging by the cacophony of photos and people's sigs, I'd always describe 532 as "about as green as it gets" and anything lower to be trending towards the blues. Such a colour has actually put me off buying diode greens, as I like blue, and I like green, but not the two of them mixed.

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Hap said:

*sorry for the bump-up*

Glad I found this thread. Im trying to go for a complete rainbow right now, and trying to found the "purest" looking green out there. I was originally going to go for 532, but as many people have said 525 is around the sweet spot it seems like 520 would be closer to true green!

JetLasers has some 70mW 520 units so I'll probably skip that instead of the 532's. Anyone here who owns a 520. What's the duty cycle like? I had a PGL-III-A awhile back at <5mW of 520 and it could only be run for like 1min, which sucks! If im not mistaken 520 diodes give off a lot of heat, no?

Thanks!

-Alex

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