there are other factors= beam profile- divergence- cost -bare diodes vs working modules etc.
I really like the 515nm 15-25mW complete green module(standard chrome plated brass 12x30) from AixiZ $85 ready to fire up with ~ 3.2 vdc
rock steady and 'Plug n play'(needs a better heatsink IMO)-I tested five on a LB1 and all made 26mW-
I hope it's not absolutely inappropriate to contribute with a few pictures I've managed to take today, on the 7th of March 2014 inside my apartment. They're solely for comparative purposes only and are of basic nature only to underscore colour differences between three green wavelengths: 515nm - 520nm - 532nm.
The way my DSLR Nikon D5200 captured all three of them quite well reflects the colour I can observe "live" while looking at the beams (the safe way, of course). During photo-shooting OD7+ goggles were applied.
These three lasers were used: Skylaser/laserbtb 30mW 515nm (LPM'ed at 41mW)
Blord's 100mW+ 520nm (LPM'ed at 115mW)
Skylaser/laserbtb 150mW 532nm (LPM'ed at 220mW)
Triplets, yet different. Defocused a lot.
Beam "dots". All shot at cca. 50cm distance on a white wall background.
Door comparative shot. Distance of cca. 5m. Focused towards the beam dots.
Middle section beam focus.
Defocusing in three stages. A gradual colour shift is to be observed.
Three beam section focusing of 515nm beam at short distance of cca. 50cm.
At the aperture.
Towards the end within the frame shot (actual beam went on for cca. 5m).
I have a laserBTB 515 pen now that looks bluer than the 520 i had and sold a while back...Its certainly a unique color. i like it, but more so, i like how it makes the difference between it [515/520] and 532 so pronounced.
Thanks everyone for the kind words:beer:. It's quite interesting to discover how much the green wavelength spectrum tends to change in colour gradually where there's a discrepancy within a few nm range to watch while going down the 520nm road and lower. Wish I could get my hands on one of the rhd's 510nm handheld units as to be seen here:
And that was like more than 2 years ago now! I hope we will eventually witness 510nm and 515nm direct green diodes in portable form while to choose from several sources (Skylaser isn't too bad as of now).
In theory, 532nm should be brightest, as it is closest to the wavelenth 550nm which cone cells are most sensitive to, and in response to some comments above, the colour should actually be noticeable, take 532 and 520 as an example.
It's not hard, it's actually impossible. Laser sources sit right on the outer edge of the CiE chart, and well outside the gamut of any camera consumers can access. Because of this, the camera must approximate. And how each camera handles such extremely saturated light is a function of each camera's sensor and firmware. The best we can hope for is to shoot pics like gismo's and tell everyone that the photos "look right" compared to the live scene.
On top of all that, lights in the 480-520nm range are the absolute worst to approximate, for two more reasons.
First, the 480-520nm region is notable in that you see large hue shifts over small wavelength variations, more so than any other part of the spectrum. On the CiE chart, you can see the "stretch" of the 480-520nm range is large compared to any other 40nm segment around the curve. So not only would small variations from camera to camera result in big potential "wrong" hues, but the human eye itself also varies for genetic reasons. If you want to start a fight among light nerds, shine a 495nm light around and ask them if it's blue or green.
Second: if you look at CiE charts with gamuts on them, you'll notice that for all of them, the biggest out-of-gamut area is the one to the upper left -- the saturated blue-green space, of course. All these lasers are up there.
So, in summation: if you could build a tuneable laser that covered the 480-520nm range and slowly adjust from one to the other extreme, you would find that any camera would tend to render it all green or all blue for a good part of the time, and would then quickly "snap" to the other at a point which would vary by each camera. Light a scene with nothing but 470-520nm light, and you'll get bigger variation among diffrent cameras than any other scene. That's why places like the Long Beach Aquarium are a great torture test for camera color accuracy.
So long as we shoot just the pure sources, it's never going to be better than "this looks right" approximations.
There IS a way to accurately capture *hue* in the sRGB space, however: you have to desaturate the light. That moves the light color away from the saturated edge towards the center of the CiE chart, and therefore into the sRGB gamut of your camera.
The only way to do that in physical reality is to mix your source with neutral white light. You set up a white card in a room with a neutral white source, and then set white balance and exposure so you get neutral grey color from the card, with R, G and B values ideally around 128, 128,128.
Then, diffuse your laser and shine it onto the white card. You want the intensity of the laser to be enough to significantly color the scene, but not enough to overexpose it. All RGB values should be less than 255. If your camera has zebras or RGB histograms, use them - you don't want any clipping.
I've been meaning to test this for a long time with a range of LED sources I have in this part of the spectrum, but I'm pretty confident in the theory.
Great thread indeed! I've had my eye on DTR's NDG700 520nm diode module for my second build. I'm just concerned I'll get it built and be left wishing I had the intensity of a 532...
Now hearing the 520 might actually be brighter in terms of Scotopic vision than the 532... I guess I just want something that will be significantly brighter than the 1W 445nm C6 I built, as well as my WL 1.4W 445nm Arctic S3...
Decisions decisions! :shhh: