In light of the Crizal UV information with respect to how AR coats reflect UV light how is it that transitions are said to perform better with an AR coating applied when it would seem that the coating is bouncing the UV light necessary to activate the lenses before it reaches them?
Crizal has a backside ar so it doesn't interfere with transitions. Im not sure if that answers the question tho
That wasn't the question. The information presented when Crizal UV was released was that all AR coatings reflect UV light (except Crizal UV now) so if all AR coatings reflect UV light then how is it that transitions performs better with an AR coating if the coating is reflecting the UV light before it gets to the lens?Originally Posted by chaoticneutral
Crizal was released before the current marketing pro's were on board.
NOW GET WITH THE BULL...UMM...PROGRAM!!!
The problem is that Avance is the best AR out there for the money imho.
Last edited by Uncle Fester; 03-15-2014 at 03:18 PM.
Because they don't block ALL UV just more than plain lenses. The Crizal UV is about equivalent to an SPF 25. So...AR lets more light through the lens instead of reflecting it, and enough UV to activate the Transistions.
I was referring more to information like this and this question has nothing to do with Crizal lenses whatsoever except the information that came to light with the release of Crizal UV with respect to the reflective properties of AR lenses.
Last edited by edKENdance; 03-15-2014 at 03:34 PM. Reason: formatting
Does this say what I think it does?
Transmittance and reflectance calculations
All transmittance properties for visible light, UV-A, and UV-B were analyzed according to the U.S. nonprescription sun eyewear standard, ANSI Z80.3-2001,16 because the prescription lens standard, ANSI Z80.1-2005,17 describes only how to calculate mean UV transmittances but makes no recommendations regarding visible or UV transmittance.
Transmittance requirements for UV-C are not included explicitly within any standard. However, the occupational safety eyewear standard, ANSI Z87.1-2003,18 does define “effective far ultraviolet,” which extends from UV-C to UV-B (200-315 nm), but clear safety lenses (i.e., visible light transmittance >85%) are exempt from this requirement. Nonetheless, UV-C transmittance was calculated using an equation similar to those for UV-A and UV-B transmittances, as described in ANSI Z80.3.
Reflectance characteristics also are not included in any standard but were analyzed for visible and UV regions using procedures similar to those defined above for transmittances. Reflectance was calculated only with regard to the specular performance of the lens. An integrative procedure to determine the overall amount of radiation to strike the eye and adnexa, along the lines used by other researchers,14, 19 is not relevant here because the only interest of the current study was to determine if, and how much, a particular lens could reflect UV radiation.
To clarify for some maybe missing to what Ken is referring, the study released data that all traditional ARs, including the pre-UV Crizals, INCREASE UV reflection compared to uncoated lenses. It's not something one would think about, but while ARs were decreasing visible spectrum reflectance they were increasing the UV. AR lenses were demonstrated to reflect more UV light off the of the lens, most consequentially off the backside and into patients' eyes, than uncoated lenses. Crizal capitalized on this to add the UV factor, which either absorbs or transmits (I don't know which) UV, instead of reflecting it.
Ken's question is if A) traditional AR reflects more UV (preventing it getting into the lens), and B) UV is the primary activator of photochromics, how can photochromics perform better with AR?
Great question, I don't know either. My gut reaction would be what Fester said, that photochromics really never did perform better it was just Essilor cross-marketing Transitions and Crizal. But the question still remains wouldn't AR DECREASE photochromic performance by denying some of the activating UV?
If Crizal's UV absorbs, it wouldn't change anything. If it transmits the UV like visible light, then they could argue Crizal UV is better with Trans because now it carries the UV through the coating to the photochromic layer.
I'm sure it's only a small effect either way, but yes I don't understand the claim of AR improving any photochromic performance.
I wasn't aware of any improvement in photochromic performance with the use of AR, except for an increase in visible light transmission. However, if they've been able to increase UV light transmission through the AR stack and associated top coatings by reducing UV reflection, without absorption, then I would expect some improvement in photochromic performance with the newer AR coatings, although I would think that the difference would be minimal.
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
My take would be this: In an old LifeRx class I had decades ago, it was stated that the A/R - photochromic symbiosis was enhanced because the A/R lens is clearer than a non A/R lens. Add to the equation the fact that the photochromic lens always leaves a slight tint in the lens material, even indoors (through as we all know, some are worse at this than others...), and the addition of A/R could be seen to enhance the transmittance of visible light to the eye - which would make a photochromic lens with A/R *appear* to be lighter, quicker than the same lens with no A/R. Are you with me?
So if you have a photochromic lens, with no A/R, then you kinda have a double whammy against visible light transmitting through a given lens indoors. You have the loss of light from surface reflectivity, and you have the added loss from the always present slight tint of the photochromic molecules in the lens as well. Capice? :)
That's all true, but the topic is invisible light (UV), not visible spectrum light, and why less is more.
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
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