Exchange red for green, if this is our only option.
YES!
Eeeh? How about no?
Above I was speaking about the λ/4 MgF2 550nm, a coating centered in a frequency of green (in the middle of the 400-700nm visible spectrum), which is a common low cost coating. This coating gives lenses a very subtle purplish colour, this is most noticeable when a source of light is seen reflected over its surface, makes it look purple. I am right now looking at an incandescent lightbulb reflected over the lens of an S21A I have at hand, and the bulb indeed looks purplish over the lens.
People is complaining about the effects of the standard anti-reflective coating in flashlight lenses. This is because the anti-reflective coating changes the tint of the beam, raising its Duv because of somewhat more green output. We already have enough green in most production led emitters, this is not what we want.
You said “I will change the blue ar-coating or the red into a green ar-coating”, but what does this mean?
If you change the anti-reflective coating for a different one without knowing the actual effects in the beam tint, how is this going to be a solution?
Plain or uncoated lenses are a known solution. 100% sure.
Yeah, what Barkuti said. If knowingly new AR coating will eliminate Duv raise then it’s ok to change process, otherwise plain and simple uncoated lenses are just perfect.
Ar coatings that show green reflections will lower Duv. If that’s what Simon means, then this would be an even better solution than uncoated glass.
Are you really sure about this?
If Simon wants to endorse some new product, I can understand. But from the perspective of a buyer, a new product must provide a useful, advantageous reason to be.
I could for example say that, if aiming for lenses with a double coating, one could be set at 475nm (at the cyan dip the usual blue pumped white leds have), and the other could be centered at 650nm (to boost reds). I've checked a few led spectograms around here to conclude this (1, 2, 3 and 4). This would cover the visible spectrum a lot better, while a double coating may still be affordable.
Still, plain or uncoated lenses are a sure win. They're also the cheapest ones so, how about some uncoated lenses? ;-)
Ultra clear (low iron) glass without coating would be my preference as well.
But again, if an AR coating(s) must be used, make sure that the reflections are green and NOT red/pink/purple.
Yes, I’m sure. The advantage would be higher transmittance than uncoated glass and improved tint (lower Duv).
I have confirmed myself with my own examples of “green” AR coated glass that it does indeed slightly decrease Duv.
Price shouldn’t really be a concern. Simon’s current AR coated glass for the C8 is $3.94 for a set of two. I’d gladly pay a few extra cents for an improved coating. That said, clear uncoated glass would also be preferable to the currently available AR coated offerings.
Just curious but, what type of anti-reflective coating is that which shows green reflections? Could you elaborate a bit more?
I guess these red/pink/purple reflections you mention are the ones I see in the glass of my S21A, and as far as I know in this regard (not a ;-) lot) these must be a sign of a λ/4 MgF2 coating centered at 550nm.
Now I could say here we come back again, I opened a related thread many months ago (About lenses and anti-reflective coatings: a call for stepping up the current technology). Also found this VY Optics page on anti-reflective coatings, where about the same is discussed. But again, these (VIS 0°, VIS-EXT) nice coatings only make sense here if there's a cheap ;-) way to get them.
Ultra clear (low iron) glass for the win! :THUMBS-UP:
I don’t know what type of coating it is as I don’t work in the optics industry. I just know it shows green reflections.
A good example is the front glass that comes installed on the D80v2.
I agree. I don’t know if it’s visible in the picture, but IRL D80v2 has definitely lower duv than A6 with the same LED.
In the graph you showed from the article you can see that UV-VIS is more effective in the blue and red range compared to green, so the reflections are going to look green, and duv will decrease.
Looking at camera lenses you can see different reflected colors from each lens, orange, cyan, green… etc from different types of coatings, combined it ends up neutral.
In order of preference (in my opinion) :
1) AR with higher red and blue transmission, reflects more green, decrease duv/improve tint, higher overall transmission than plain glass, i.e more efficient.
2) AR with close to neutral transmission, higher transmission than plain glass. (those are probably more expensive)
3) plain glass (of good quality or course, as you mentionned not with iron (green) impurities).
4) currently offered AR lenses : higher green transmission, reflect more blue and red, increase duv/degrade tint. Higher transmission than plain glass.
Thanks. So indeed other types of coatings are being used, which after all means it is inexpensive or affordable to get a hold on them.
Useful information, thanks.
From the previously posted graph, I think VIS 0° is top choice, with comparatively better transmittance of red frequencies, excellent balance and should also lower Duv a tiny bit.
Still, can't help saying that uncoated lenses are perfectly balanced and cheap.
Another option is to use a completely transparent antireflection film.
The new Osram centering ring for the L21B seems to work well:
My reflector was a bit dirty though it’s only noticeable when the light is on:
Ooo, finally a black centering gasket. I like it.
I think you mean to say anti-reflective film. ;-)
I have done a quick search about transparent anti-reflective film and found certain information, although I'm not going to go on with it now because at this moment we certainly don't know what type of technology are you speaking about or can get a hold of.
However what I can certainly say is that if you can get some example lenses, from what I can see here in post #5463 it is clear that you can certainly test them to know if they will be liked. The goal is:
- Lenses or lens coating must not raise Duv; if they lower Duv a tiny bit it can be nice.
- Beam CRI or CRI with the lens on must be as good as it is without lens (R9 should not go down, and etc.).
Just in case, without any sort of testing it can be clearly understood that uncoated quality lenses meet both conditions. O:)
Well just a curiosity,what happen on the tint if the coating instead of violet will be Rose?
That would be interest if decrease Duv without intact CRI
Simon, a couple of months ago you mentioned the 3X21A had a triple XHP70 in the works. Any time frame for pictures or release?
I have a question, which is a sincere question. What is the purpose of anti-reflective coating on our flashlight lenses? Is there some kind of glare that it eliminates ? If so is it glare on what we are lighting up or from the lens itself?