Hm... I just looked, and it seems that a 28.6mm lens will work if you squeeze it in or get a different oring than the odd "shaped" one in there now.
Inside diameter, without Solarforce rubber grommet.
Thanks! Now I feel better about the lens....
Youre right srfreddy. sorry for the confusion. I never even tried it with the rubber "o-ring" off. I value waterproofness as I have and will drop my flashlight in puddles, etc. That o-ring creates a really nice seal.
I apologize for not fully investigating the issue though
Man, I've just checked my standard L2P lens, and... it's crystal clear :~ If I don't count reflections, I can say the lens is not there, can't really see it. So why coated lenses are better?
BTW, my ITP and Kingpower lenses are AR coated, and they don't have that bluish tint :|
Coated lens are more clear, and don't reflect the whole spectrum.
Even more clear? Really can't imagine a clearer lens :bigsmile: Will need to buy one to see it by myself.
There are lots of reasons to use coated lenses on flashlights but more brightness out the front isn't one of them.
Transmittance depends of the refractive indices of air and glass.
T = 4*n1*n2/(n1+n2)2 for each air-glass surface If we assume n = 1.0 for air and 1.5 for glass then T = 0.96 for the each surface and 0.96*0.96 = 0.92 for both
If we pretend that our coated glass transmits 100%, which it doesn't by the way, then there will be 8% more lumens out the front.
Would you see any difference in the brightness? [1]
Unfortunately the real world transmittance of the best coated glass is more like 0.98 for a single surface or 0.96 for both.
In this case the improvement would be only 0.96 - 0.92 = 4%
Would you see any difference in the brightness this time? [2]
The honest reason for using coated glass in flashlights is for aesthetics, not for performance. And of course there's nothing wrong with that.
Cheers,
Angus
[1] [2] Honest answers please 
I got a huge difference in my lights.
OK, the original lens was filthy. I reckon that for my lights I'd not get more of a boost any other way for $3.
But if you keep them clean the difference is a lot less. I still got a visible difference even with a freshly cleaned plain glass lens.
I got 870 lumens at switch-on with a new coated lens compared to 796 with a (dirty) plain glass lens that came with the light. Once I'd cleaned the lens and put it back, it still gave a lot less than the coated one did. I forgot to record the numbers on a spreadsheet but there is a thread around here saying what the results were.
http://budgetlightforum.cz.cc/node/1026 Thanks Don, there's your lumens recorded in that thread, with some other users that are even greater. I would have never thought coated lens would make any difference, unlike camera lens or eyeglasses. But light meters don't lie.
But angusinalberta brings up a good point ... "Would you see any difference in the brightness?" Really, I dunno. But for $2, I've spent more on tethers or gitd o rings that have no effect of lumens 
I have a suggestion for measuring the transmitance of glass lenses that will keep all confounding variables to a minimum. I don't have any coated glass here to do the experiment myself or I would.
Place the lens that's to be tested over the light meter instead of the flashlight.
This probably requires a black cover over the light sensor with a hole a bit smaller than the lens cut in it.
Shine a steady light on the meter and record the following readings;
a) no lens over the meter
b) uncoated lens over the meter
c) coated lens over the meter
Repeat 5-10 times and calculate averages.
Transmittance of the uncoated lens = bave ÷ aave * 100
Transmittance of the coated lens = cave ÷ aave * 100
Prediction: no more than 4% to 5% difference between the two results or I eat my hat.
Cheers,
Angus
The Flashlightlens.com UCL's are something like 99.2% transmittance, IIRC. a
Be an interesting test, and I agree would most liklely result in a 4-5% difference, probably much lower. But it would not be a very practical test, as it would only measure the translucence of the glass alone, and not the overall translucence of the glass combined with the compounded refraction of the reflector to glass. Buried in the original thread is an interesting wiki link to thin film interference (http://en.wikipedia.org/wiki/Thin-film_interference). Of particular note in this article is the phase shifts on what is termed constuctive vs destructive interferences - which would not be measured by your scenerio.
um, I think. :-)
That's in agreement with wikipedia
Reflectance of 0.5% implies transmittance of 99.5%
0.9952 = 99.0%
I wonder if DX lenses perform as well.
Worthy of a comparison test?
Cheers,
Angus
Not at all, it is a very practical test, in that it tests one variable, the effectiveness of the anti-reflection coating. All other things, lamp-meter position in particular, remain exactly the same. In science it is always preferable to change one, and only one, variable at a time.
Another excellent wiki article is at http://en.wikipedia.org/wiki/Anti-reflective_coating
It explains how the transmission of light through an air-glass interface is enhanced by destructive interference of the light that would normally have been reflected if the quarter wave thick coating were absent.
Hope that last sentence makes sense to you. It's past my bedtime.
Cheers,
Angus
Actually, it does. But of course enhanced by the six pack of excellent local micro-brews been thoroughly enjoying tonight.
Tomorrow morn will probably have no idea what you, or I, were discussing.
Cheers my friend, Tom
My glass needs replacing .I like my light . I’m tired of garbage .I want more output too .4 more good reasons to buy good A/R glass…
Don ...easiest answer is quit smoking ..think of the time you'll save cleaning .AND Your lights and your teeth will be brighter .
Even the dog has more sense than to stand downwind from a campfire .
Sorry guys for bringing back a deadthread but for those of us who are interested in upgrading our lights I want people to know that KD is still selling the AR lenses and I just bought a few of them (6) for testing purposes. I mean having a Bushwhacked P60 Drop in deserves a nice AR lens right? Right! I can post the link to the 28mm ones if anyone else is interested in one for their light. Mine happens to be a Solarforce L2 and, from what I have gathered, the KD 28mm fits nicely.
The real gains come when the light is hot rodded. And the best gains come from the flashlightlens.com UCL and UCLp.
I don’t know if the KD lens give any appreciable boost in output, but they sure look nice, and to be honest that’s the only reason why I bought them. :bigsmile: