In my experience better performance quite often does not necessarily involves higher cost. For me, great performance and affordable cost is a very real thing. Things change and we evolve, its all in the amount of light we let in. ;-)
Concerning what you say about the peaks in led spectral power distributions, to reduce green and blue peaks the λ/4 MgF2 coating must not be set straight at these frequencies, i.e. not “tuned” for 455nm or 550nm. Maybe a multilayer coating set at 410, 500, 605 and 670nm, or sort of. Heck, it's almost 10 AM here and I'm yet to go to bed, so we'll see later LoL.
BTW, this is not necessarily a goal worth pursuing but when you look at a lens at angle, you see a colourful residue reflection. That’s how you tell that a lens is coated.
Some lenses have the reflection very weak and white which makes it pretty much invisible.
I remember Dale saying that when he showed his lights with UCL2 lenses, he would often get fingerprints on the lens…because people would feel an urge to check whether the lens was there.
I understood the UCL and UCLp lens from https://flashlightlens.com/ were superior in that they had less impact on duv and CRI - I think TK mentioned this a while back. Anyone know if that's still accurate?
They currently sell UCL (98-99%) and UCLv3 (98-99%) in glass, and UCLp (97%) in Acrylic. The v3 is AR coated Borofloat
Yes - the UCL and UCLp I've used in the past are super clear, but you can still catch a tinted color in a reflection off the lens.
There's a ∅22.6 × 1.75mm available size, that conforms to the lens size listed for the Convoy S21A (∅22.8 × 1.5mm). However, although paying nearly €4 for a lens is a thing I could probably allow to happen, the shipping cost :facepalm: to where I live is a whole different story.
Yes, the number is the incidence angle at which the coating works best.
If you’re concerned about zoomie flood more than throw than yes, 45 would be about as good as it gets. Same with mule. If it’s zoomie with moderately strong (or weak) lens but you care about throw, the actual angles are going to be close to 0 degrees. Overall, something in between should work best.
If it’s a reflector light, beam is going to hit the lens (actually: the window) at near-0 angle. Spill - still less than 45 unless you have a very shallow reflector. I think for reflector lights the optimal option would be near 0. Considering that most coatings on the market are designed to work at exactly 0 - that’s not perfect but close.
Not aware of any tests on UCL's in general. Not sure if/where there are AR lens tests here on BLF. With all the crazy testing equipment we got here, I can't recall seeing any AR lens tests to show the changes in duv and CRI.
I've only tested for lumens and throw. I've seen maybe 2% to 5% bumps. 5% more typical from regular non AR glass.
0K but, does it really matters? Where are those VIS-x lenses, after all.
So there is a myriad of AR-coatings out there. 0K, maybe not a myriad but a nice bunch.
The question is what can we aim to get a chance to see manufactured. Since I guess λ/4 MgF2 is public domain, we could probably get someone interested in manufacturing :???: 4-layer λ/4 MgF2 coated lenses. As I see it that coating covers ±40nm very well, and so I would specify the 4 layers to be optimized for 430, 510, 590 and 670nm. That would deliver balanced performing lenses. Or it should, doesn't it?
That’s a good question. I’m truly not an optics expert and my intuition is relatively (on my personal scale) weak in this area. I don’t see how layering works honestly. I could only imagine its extremeley irradic and sort of an empirical method of discovery. What I mean is that my assumption is that the behavior of two layers is not an additive function of the two individuals, but rather something significantly different.
I’m going to buy some UCLv3 lenses and see how they look. I’ve only heard great things.
Reality is created from above to below (as above so below). It all starts with an idea, a thought pattern which is energized and eventually materializes if all its requirements are met. Thus, when something “is not known” it is a lot better to stay in a positive mindset. It's extremely important if the aim is to succeed.
I didn't create the λ/4 MgF2 coating or any of the other ones. I think multiple layers of such coating side by side results in a “flat” reflectivity curve at ≈1.3% reflectance, which is the lowest reflectance value delivered by the coating. It may be argued that ≈1.3% isn't the best thing, but everything between 400 and 700nm at ≈1.3% is excellent consistency; to preserve Duv and CRI consistency matters. For this reason I was speaking about the VIS coatings above, and also about the FS-BBAR-397-727 from Torr Scientific Ltd:
Now that I look at it more carefully, if the graph is accurate I'm not that sure. Performs best “in the green”, around 515nm. Despite performing better overall, green is not what we want.
I have noticed myself that AR causes change in output tint, never knew it will cause such a shift in duv.
Very useful info, lets get rid of AR coating and use sapphire lenses
Anti-reflective and lens loss are new domains and I’m trying to understand / calibrate my lightbox.
Just so finished making my own lightbox and I’m using a shutter diaphragm to simplify the flashlight’s different diameter insertion. But as I’m calibrating and checking against some lights, the lens’ loss varied from 8.8 to 14.9%
Some pics:
I find the loss quite high and too much disparity.
Is it normal for such losses? As I was taking the pictures, I saw that at any incident angle the shutter diaphragm wouldn’t show - too much reflectiveness. Without a backlight and some fumbling, I did get that one picture.
And as for the variations of loss, although I take care to position the light dead center and open the diaphragm just a 1mm or so around the light’s window diameter; yet I get varying losses from Convoy S2+ (4500ºK) to Sofirn’s SP33 (V2 - CC driver) (5000ºK).
Huh? I don’t take the light’s lens off. What I call the light’s window is what is colloquially called the ‘lens’ but as this has no focusing properties but a retainer I prefer the term ‘window’.
AR coating basics are simple from the optical theory point of view.
When light passes between 2 materials, part of it reflects and part of it refracts.
How much? If one is interested, Fresnel equations let you calculate that. But I won’t explain that to you as it’s not necessary.
What you need to know that at 0 degree, there are only 2 things that affect the amount reflected:
refractive index of the first material
refractive index of the second material
Furthermore, reflection is directly proportional to the square of their difference.
So the idea is to introduce an intermediate material with intermediate index.
Light doesn’t reflect between air and glass, but first between the air and coating and later again between the coating and glass.
But magnitude of each reflection is much smaller and the total is smaller as well.
Multilayer coating simply adds more layers to the stack, dividing the difference between refractive indices to even smaller parts.
And there’s no trial and error in coating design. Coating designers know what materials they can use, they know the refractive indices and can easily calculate the final performance.
There are no multiple layers of MgF2. MgF2 has always the same index so adding more layers doesn’t help. You need to use more material to make a multilayer coating.
Thanks, Agro - detailed explanation of refractive indexes.
But my query is why do I have such differing lens loss through the shutter diaphragm? And the upper value of 14.9% is out of the realm. Yes, there could be as much as 4% going in as well as out (total of 8%).
I looked over the shutter lens and doesn’t seem to have any AR - surprising as this was taken out of a camera lens attachment. Also, I had taken the time to clean all the lenses (shutter & flashlight) with alcohol prior to any testing. My test is rather simple: measure the lux without the shutter and then with the shutter. As for the shutter opening, as the glass plate is some 1mm above, I allow about 2mm larger opening than the flashlight aperture.
Could the difference in LED CRI affect the difference in light transmission? Or for that matter, the tint?
It would take refractive index of 2.15 to get this kind of loss. There are also transmission losses, so maybe a little less…but why would they use a glass of this high index? This does not seem like a good explanation.
Maybe there are 2 pieces of glass?
Here we get into advanced stuff…
More advanced coating exploits wave phenomena to improve performance at certain beam wavelengths.
I have basic understanding of it but I can’t explain it better than the documents Barkuti linked to.
Yes, coatings actually have different performance at different wavelengths, therefore changing LED spectrum affects transmission. But higher CRI? Higher CRI has the blue peak smaller. If coating is relatively good near this peak, higher CRI will perform worse. If coating is relatively bad there, higher CRI will perform better. CCT should have higher effect on coating performance though.
I understand basic refractive indexes, and how due to the square in the equation, more smaller steps equals less overall reflection. I was sorta clueless as to the additive properties of the reflectance vs wavelength curves. I’ll give this topic a read sometime… Currently overwhelmed with other things at the moment.
of. Heck, it's almost 10 AM here and I'm yet to go to bed, so we'll see later LoL.
I better understand now.
