The tested lenses are larger so what I did was taking off the S21D’s OEM lens, then placed the tested lens by holding it, recorded the number, then put back OEM, recorded another number. I did about 4-5 runs or so for each lens, sometimes more. The flashlight was set at 35% brightness and let sit for 15 minutes or so before measuring. I decided to use the middle-of-the-road 30° bead TIR optic this time.
With flashlight mounted on tripod (hence no shaking), I’ve found the Opple Lightmaster Pro (aka Series 3) to be incredibly consistent in its reading of Duv (and brightness & Ra etc.). It reads the same x,y coordinates down to the fourth significant figure between different runs. As such it is a great meter to do comparison work; just remarkable considering how cheap it is. I recommend it extremely highly for anyone into LED collecting.
Duv values for Convoy S21D with Nichia 219b 4500K
The color refers to a reflection of ceiling light bulb, NOT any tint I could see.
Home test for fun, please take result with a grain of salt. There might also be some correction as I double check data.
1. No lens: –0.0127 2. Convoy AR Green-reflection lens : –0.0124 CCT 4471 3. Wurkkos Non-AR: –0.0123 4. UCL AR Blue: –0.0123 5. UCL AR Purple: –0.0102 (Duv change: ~0.0020 more positive) CCT 4365
I find it interesting that the lens with the highest transmission rate, UCL Purple, is also the one that affects Duv the most. Next - beamshots to see if this difference matters in real life scenes.
Green reflecting coating is supposed to prevent green tint from getting thru.
As we see from your test, Blue reflecting coating works Just as Well!
The Acrylic w Purple coating lets the most green get through, thereby raising the DUV by 0.0020 compared to the green and blue coated glass. It may not be the fault of the coating, since Acrylic transmits more light than glass, it may also be transmitting more of the Green tint, thereby raising the DUV.
The tripod hold I use is this (a legit seller) HERE . It is much better than the small rubber without velcro. I’ve found keeping the light stable is the first step towards measuring reliably, especially for the throw where you have to keep hotspot centered on the sensor.
Thanks Jon. From what I have read (meaning I’m no expert), AR coating targets a wavelength that’s close to the center of the visible spectrum (which is yellow green as explained in article below) and as a result proportionally more green will go through with all AR coating, including Convoy’s. The difference is only how much green, as seen here obviously the Convoy is best, and UVL Purple an outlier worst. To be fair, outside of the UVL Purple, the difference among the lenses is small (it’s in the 4th digit) and within error limit of my amateur testing rig for example, even as I’m quite confident of the result.
A good article on this subject http://rick_oleson.tripod.com/index-166.html
So, if coated lenses are purple, won’t my photos have a purple tint?
No…. actually, they’ll have a slight yellow-green tint – the extra light that didn’t get reflected passes on through to the film, and there’s a little more of the 550nm yellow-green than there is of the other colors. But it’s not very much – glass only reflects about 4% of light from each surface to begin with, and the coating has some effect at all wavelengths – so there’s maybe a couple of percent of extra green light getting to the film. For most normal photography, this isn’t enough to be noticeable in the pictures.
Btw the Duv test between 1 and 2 (lens vs no lens) should be easy to do for any Convoy owner with Opple 3. I hope to see similar comparison from other owners, especially people who have the infamous lens w/ purple reflection. That way we could compare/correlate our findings.
I think either a. measuring Duv or b. comparison photography (as opposed to visual observation) are important to have some fun with this :-).
I would like to get a hold of Convoy’s lens with purple reflection but can’t find it on AliX. Would very much appreciate anyone who has spare putple lens for any of my Convoy to send it to me . I’ll pay shipping and lens cost of course.
In comparing Duv number, I’ve noted that if the change is in the fourth number after decimal point, for example
“No Lens”: –0.012 7 versus “Convoy Green-reflection”: –0.012 4
it is not easily noticeable on the Duv graph.
What this means is, at least per my test, unless I develop Superman’s vision, I am not sure that I could see a difference between for example No Lens versus Convoy Green Reflection versus UCL Blue. I plan to take beamshots against the wall of truth to confirm if this is true.
OTOH UCL Purple versus Convoy Green Reflection is a bigger difference (it’s on the third number after decimal point) and likely will be seen on Duv graph.
Visually if you compare some 519A lights with different lenses, the difference in DUV is visually noticeable. However if you then add other emitters into the mix such as SSTs and LH351D, then you realise that even the “worst” 519A/lens combination is very neutral and perfectly acceptable.
It's difficult to see a duv difference when both outputs are way into the magenta region--the percent difference between the two is tiny compared to their deviation from the BBL. (Imagine trying to discern between 1 and 10 lumens, and between 1001 and 1010 lumens. The absolute difference is the same, but the percentage difference is huge!)
I also suspect that the green AR lens would make a larger duv difference numerically with a light source that starts off as neutral or slightly green. If the emitter starts out magenta, there is little green to begin with, and not much removal can happen.
It would be lovely if the test could be re-done with emitters that are neutral or slightly green.
Thank you Haukkeli for linking the test! Looking at -0.003 decrease in duv from swapping purple to green AR. That's a LOT of green reduction if the emitter starts off close to neutral. Also, the +8 increase in R9 is really something.
I would actually expect a more drastic difference for Convoy lenses--their purple reflection, at least in my sample of Convoy lenses, appears much more intense than the lens shown in the D80 photo.
Thanks everyone for your input and @Haukeli great job for finding that post of Djozz’s test - thank you. It’s great to see someone else’s numbers to know I am not entirely lost lol. At any rate after looking at Djozz’s results, I have just rerun my test not just with 219b but also with 519a in my S21D using 60 Bead TIR optic, and could now confirm with near certainty my result .
For Convoy S21D with Nichia 219b 4500k: 1. No lens: –0.0127 2. Convoy AR Green-reflection lens : –0.0124 CCT 4471 3. Wurkkos Non-AR: –0.0123 4. UCL AR Blue: –0.0123 5. UCL AR Purple: –0.0102 (the Purple Lens’s Duv is “20 points” (0.0020) more positive) CCT 4365
Note that we know changing lenses affect Duv, but not frequently mentioned is it also shifts CCT about 50-100 points.
Where my result is different from Djozz’s - I found essentially no significant difference in Duv among set-up 1 to 4 above.
Where my result is similar to Djozz’s - The UCL Purple AR turns Duv approximately 0.0020 more positive (note the decimal point) and drops CCT roughly 50-100 K versus the group of 4 above. Not a huge change numerically, but definitely there, and does bring beam into more yellow-green territory.
Thank you @cannga for re-doing the test! Would you share the numerical results for the 519A? (I assume the graphic you shared is for 219B given how low the duv is.)
I swapped out a purple AR coated lens for a non-coated one in my 519A 5700K triple and noticed a huge difference right away. In addition to eliminating much green, the tint shift is a lot less, due to the fact that an AR lens does not alter tint equally in all directions. It alters tint the most near the center of the beam, but barely does anything to tint near the periphery of the beam.
I just ordered some green AR lenses and really hope they will bring the duv down more and eliminate angular tint shift completely.
You’re very welcome. Data from S21D with 519a 4500K and 60 Bead TIR below, very similar behavior to 219b 4500K. Again the UCL Acrylic Lens with Purple reflection is an outlier and the Duv shift is again around 0.002, CCT drops around 50-100. I could provide x,y coordinates if you’re interested.
S21D 519a 4500K with 60 Bead TIR 1. Convoy Green Reflection AR –0.0038 CCT~4041 2. No Lens –0.0037 3. Wurkkos Non-AR –0.0034 4. UCL Blue AR –0.0032 5. UCL Purple AR –0.0018 CCT~3985
Above bolded part in your post very interesting; I didn’t know that. Was about to write that any effect from an AR lens would not affect tint shift since it alters the whole field. Always good to read a second time before responding :person_facepalming: :innocent: . But question: if AR doesn’t alter peripheral field, it wouldn’t help with the peripheral tint shift in this Nichia would it?
I actually found the tint shift in my 519a 4500K not that bad especially w/ wide & beaded TIR and in actual use (vs white wall beamshot). Compared to my beamshot is it worse in your 5700K version?
Thank you so much for the data! I must say that I am very surprised by how little the green AR on Convoy lens changes the tint.
Regarding your question: I think green AR helps with tint shift precisely because it does not affect the periphery much. In a typical TIR setup, the beam tends to be greener at the center and pinkish at the boundary. A good green AR lens should take out much green from the center but not remove green from the boundary, thereby eliminating tint shift.
The 519As actually start out without too much shift (way less than the 219Cs that were in my light before), and however much shift that does occur cannot be accurately captured by a camera, so I couldn't make a reliable comparison to your beamshots, unfortunately. My 5700K triple is under medium spot frosted (Carclo 10508) TIRs, and with a non-coated glass the tint shift is ok enough that you probably won't notice unless you know it's there. With a purple AR, however, the beam turns to fried egg and the tint shift is very obvious on a white wall and in real world use.
It’s numerically small but is noticeable as other users have noted (stephenk above). I am glad that my result is in the range of Djozz’s test. His change between green and purple was about .003, mine is .002.
For those new to this you could very roughly see what the change in beam color is by enlarging the pic below and look at the color field that each of the dot is in. It does become a little more yellow-green with the purple AR lens.
I plan to take A vs B picture of actual scene (wall of truth in my living room ) for further comparison between green and purple.
The data jon_slider linked is very interesting, in contrast to cannga's data, as the purple AR appears to have less of an effect compared to green AR. Perhaps variance between batches is too much to allow a definite conclusion.
It’s confusing because of the way he presented data, but actually there’s no contradiction. (Jon thanks for the good find.)
I’ll list results that are common to all 3 tests: 1. Green more negative than purple: no contradiction here. Reddit poster’s result is –0.001, Djozz’s is –0.003, and mine is right in the middle –0.002. Coincidental or not they are actually remarkably close. 2. All 3 values are NOT that significant as far as effect on beam color (EDIT: wrong lol, as shown later, yes even 0.002 is a big difference) is concerned. Mainly because they are only third digit after decimal point and of low values (1,2,3). 3. In fact it seems so far ALL of the values listed for non-AR lens, no lens, green lens, purple lens, etc., are in the 0.001-0.003 range of each other (low value, third from decimal). Meaning this type of AR related tint mod is not going to change your beam color significantly.
IMvHO, outside of beamshot /white wall comparison, the best way to gauge Duv effect is to graph them on the BBL curve (NOT listing percentage like reddit’s poster). An example is pic below, where you could see a Duv change of 0.002 doesn’t alter beam color that much. I am actually very curious what the beamshot will show.
Thank you for the summary and sharing your perspective! I will add some of my thoughts...
I completely agree with Claim 1, and don't have enough info to comment much on Claims 2 and 3. I suspect that some really bad purple lenses I have incur a more than +0.003 shift, but don't have the equipment to tell. I might also add that the threshold for significance might depend on how tint-snobby someone is, and I personally find a change on the order of +/-0.003 very noticeable even without comparison, if the emitter is close to neutral.
I agree that there is no contradiction, but do maintain that there is inconsistency between batches. I am comparing the absolute-differences |Green - None| and |Purple - None|, and for the reddit data the green absolute change is greater, while from your tests the purple change is greater.
I do agree with you that plotting in color space is an excellent way to gauge duv, but I think the choice of 219B is suboptimal--I find the existing tint deviation of the 219B too large, on the order of 0.01. On that note, I would love to see plots of your 519A tests in color space!
I will respectfully argue that percentages are a very helpful way to gauge duv in practical terms. On a related note, I claim that the implicit question "is +0.003 duv significant?" is ill-posed without reference to the initial duv before the change. If an emitter starts off close to neutral, +0.003 would be a huge percentage of the existing deviation, and I feel many tint snobs will spot the difference. However, if an emitter starts off pure pink, +0.003 constitutes a very small percentage of existing deviation and would not result in a very noticeable difference: lots of pink plus a bit of green is still lots of pink.
I will go back to a previous analogy: is +10 lumens significant? Yes, if your light is currently off, which corresponds to an infinite-percentage increase. Arguably no, if your light is already at 1000lumens--I doubt many would notice the 1% increase.
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) for further comparison between green and purple.
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