I came across this short video from Huygens Optics that does a great job of explaining how anti-reflective (AR) coatings work. The refractive index of the coating matters, but the thickness of the coating can also greatly improve performance, albeit only at a specific wavelength.
Based on this, I suspect the coating thickness may be driving the color of AR coatings - if the coating is a little thicker or thinner, that changes what light is most strongly impacted by the coating. If anyone knows if there are other factors at play here (presumably the composition of the coating?), I’d be curious to hear.
(The entire “Huygens Optics” YouTube channel is interesting, at least for people who like to nerd out on the physics of light, how lenses are made, etc.)
You might be right. I’ve seen alot of AR ranging from a deep pinkish maroon to golden green, to typical glass green, to indigo, to purple. I actually have 2 of the mentioned “colors” in front of me now, and the AR can be seen at specific angles. Cool vid!
**my eagtac has an indigo/purple,
kr1aa and d3aa has a greenish yellow,
novatac has a greenish,
an older foursevens mini turbo is purplish red, but I have to double check..
generally, it seems like alot of my chinese made lights have some purplish AR, and it seems like it might affect the DUV, as those beams look extremely green. The Kr1AA and d3aa being the exceptions, but perhaps someone who has an opple can test chromacity with and without the AR lenses?
I took it from my archive. I could potentially try it without the lens when back home if not too tricky. However, I bet the duv will be between those two values I already measured.
Based solely on numbers, I’m inclined to agree, but is the transmittance value based on quantitative volume of aggregate light, or qualitative volume? i.e., if I filter some of a specific wavelength, if the intensity didn’t decrease substantially, would it still be the same quality of light and maintain an AR transmittance rating of 94%?
What I found (from many hours wasted ); hope this helps. The best/surest way to test, for me anyway, is to place flashlight under a ceiling light bulb, then look for that light bulb reflection on the flashlight’s lens.
Greene-reflection AR: no effect on the Duv (no change, same value as non AR lens).
Purple reflection AR: about 20 points, ie 0.0020, more positive Duv (greener tint on beam).
The reflection could have many different colors: teal, blue, etc. Green reflection is the best (no change in Duv from no AR lens). AFAIK, the few people who have tested it, found similar result.
IMHO, what I learned that was most important from my “experiment” (amateur equipment, but repeated many times to ensure accuracy) is that a Green-Reflection AR lens does NOT improve the Duv over a non AR lens. It just doesn’t make it worse (more greenish).
OTOH, a Purple-Reflection AR lens does make the beam color more greenish, or worse from enthusiasts’ viewpoint. To me, not at all worth the small and hardly noticeable 3-5% gain in output (measured with Texas Ace lumen tube, Wurkkos TS30S).
Most interesting, ALL of my AR eyeglasses have green-reflection lenses. Flashaholics fully vindicated .
same, lol…also, blue light filters, maybe? Green light isn’t necessarily JUST green light, even if it may be one of the primary photometric colors…it’s no coincidence that pigment color theory is inversely related to photometric color theory. (pseudo prosletyzing here, but it reveals a spiritual vs. physical truth. ok, done…)
); hope this helps. The best/surest way to test, for me anyway, is to place flashlight under a ceiling light bulb, then look for that light bulb reflection on the flashlight’s lens.