Weather and AR...

[AndyOptom]

So, we've been seeing progressively larger numbers of AR damage and failure across the board, from smaller labs to the likes of Essilor/Hoya/Zeiss/etc. (named in alphabetical order, just saying). From mild crazing to patches of abraded AR, we've seen it all happening at a surprisingly aggressive rate. No changes in our edging staff or lab, and the frame movement is also quite consistent (i.e. full frames, nylon, rimless, etc).

Of course, we have been questioning the patients as well as the labs, but no luck and it's come down to a staring match...

That said, here in SEA our weather has kind of gone bonkers. It currently isn't uncommon for afternoon temperatures to hit anywhere between 30 to 38 Celsius, followed by a bone-chilling thunderstorm later in the day. From what I understand of AR, this might lead to repeated expansion/contraction problems that eventually cause AR failure.

Does this weather pattern sound suspect for potentially shortening life of lens AR? Logically I think so, but given my slipping memory...

[lensmanmd]

So, we've been seeing progressively larger numbers of AR damage and failure across the board, from smaller labs to the likes of Essilor/Hoya/Zeiss/etc. (named in alphabetical order, just saying). From mild crazing to patches of abraded AR, we've seen it all happening at a surprisingly aggressive rate. No changes in our edging staff or lab, and the frame movement is also quite consistent (i.e. full frames, nylon, rimless, etc).

Of course, we have been questioning the patients as well as the labs, but no luck and it's come down to a staring match...

That said, here in SEA our weather has kind of gone bonkers. It currently isn't uncommon for afternoon temperatures to hit anywhere between 30 to 38 Celsius, followed by a bone-chilling thunderstorm later in the day. From what I understand of AR, this might lead to repeated expansion/contraction problems that eventually cause AR failure.

Does this weather pattern sound suspect for potentially shortening life of lens AR? Logically I think so, but given my slipping memory...

Any extreme temperature changes will aid in the failure of thin films due to the substrate contracting and expanding at different rates compared to the hard coat and thin films. Dip coated premium ARs will be less prone to this compared to spin coated. That said, what materials and hard coat combinations are you seeing this on?

[Chris Ryser]

Does this weather pattern sound suspect for potentially shortening life of lens AR? Logically I think so, but given my slipping memory...

My own slipping memory reminds me of the old days in Switzerland, and no acting up of AR coatings in winter weather and coming into the warm house from extreme cold temperatures or vice versa.

However in these days the AR coating was applied only on glass lenses. The SIO2 layer (which is Glass) was totally compatible with the basic glass lens and there was no expansion or contraction problems.

This all changed when plastic lenses hit the market and became the run of the mill materials for optical lenses. The plastic lens, whatever material, has a different expansion coefficient than the AR layer which is SIO2 (=glass).

When there is a sudden temperature change it just has to happen. This is no material, nor manufacturing defect, it just has to happen. I am only surprised that it happens also in your corner of the world, but then you explained also the the big thunderstorms with a sudden large temperature drop, that makes sense.

There is also one way to save a lens if it is made from the right plastic material, is to use a good AR stripper which can be done in an office in a few seconds and the lens is fully saved, with the defective AR coating removed.

If I would be back in the retail, I would only sell AR coatings on CR39 lenses which are indifferent to an AR coating stripper, which will turn most other materials into a white opaque, unusable lens.

I came out with the first commercial AR stripper in 1984 that was ready to use, with a very large dilution of the necessary acids down to 13.5%, which made it a non dangerous product for professional use, as well as transportation. We have been selling it ever since.

Lenses that have been stripped can be re-coated by neutralizing the leftover acid in the lens pores, or can still be worn and used without the AR coating.

However anybody wearing Polycarbonate or other high index lenses is out of luck, as these lenses will turn white opaque when stripping, and new lenses have to be made.

There is nothing that can be done, when sudden temperature change hits those lenses, the glassy AR coating is solidly adhering to the basic lens, and will craze when the base is expanding or contracting. No manufacturing problem in that case.

[Chris Ryser]

There is nothing that can be done, when sudden temperature change hits those lenses, the glassy AR coating is solidly adhering to the basic lens, and will craze when the base is expanding or contracting. No manufacturing problem in that case.

This is a problem every retail optician should advise their patients of, when they sell those highly expensive AR coatings.

So what can be done to get around this problem were you can not blame the lab or the manufacturer for having supplied a faulty lens ?

A)
At point of sale the customer should be advised of the fact that by purchasing AR coatings of any kind and make, added to the lens they are purchasing, can craze in mid to extreme sudden temperature changes.

B)
If the customer purchases any lens materials as, Polycarbonate or other high index for one reason or another, the lenses can not be saved if they encounter any sudden temperature changes, and the coating will craze and the lenses have to be replaced.

C)
The perfect solution is to stick to CR39 material for AR coatings, which can be saved without any problem, by stripping and recoating them, or just by using them without the AR coating.

[Trina]

If I would be back in the retail, I would only sell AR coatings on CR39 lenses which are indifferent to an AR coating stripper, which will turn most other materials into a white opaque, unusable lens.

.

I was taught that a quality AR helps the transmission of light through high index lenses, improving vision, especially at night. Not to mention the reduction of glare. I wouldn't want to sell a high index lens without AR.

[Tallboy]

I was taught that a quality AR helps the transmission of light through high index lenses, improving vision, especially at night. Not to mention the reduction of glare. I wouldn't want to sell a high index lens without AR.

I all but make a person sign a waiver if they insist on getting ultra high index (1.67 and up) without an AR

Some of those lenses will reflect close to 20% light without an AR

[Kwill212]

If I would be back in the retail, I would only sell AR coatings on CR39 lenses which are indifferent to an AR coating stripper, which will turn most other materials into a white opaque, unusable lens.

I was taught that a quality AR helps the transmission of light through high index lenses, improving vision, especially at night. Not to mention the reduction of glare. I wouldn't want to sell a high index lens without AR.

I don't think the majority of us would sell high index lenses with AR either. Chris lives on a different optical planet than most of us, and would only sell flat tops instead of PALs as well.

[lensmanmd]

I was taught that a quality AR helps the transmission of light through high index lenses, improving vision, especially at night. Not to mention the reduction of glare. I wouldn't want to sell a high index lens without AR.

A basic lens comparison grid.

[Quince]

A basic lens comparison grid.

I'm assuming 1.6, 1.7, and 1.74 are comparable to 1.67? Does anyone have any further info on how close their numbers are?

[lensmanmd]

I'm assuming 1.6, 1.7, and 1.74 are comparable to 1.67? Does anyone have any further info on how close their numbers are?

Something to geek out over. 1=T+R+A Where T is light transmitted through the lens. R is light reflected from the lens and A is light absorbed into the lens. As long as you know the refractive index of a lens, the following formula will approximate avg transmission.

And yes, the higher the index, the higher the reflectance. See below for an average interpretation.

My basic math figures 12.5% reflectance for 1.7 and 13.8% reflectance for 1.74, which correlates well to the chart.

Hope this helps

Closer to 15.4% for 1.74. Amazing when one uses a real calculator and formulas instead of running numbers by relative comparison.

[Don Gilman]

I was taught that a quality AR helps the transmission of light through high index lenses, improving vision, especially at night. Not to mention the reduction of glare. I wouldn't want to sell a high index lens without AR.

Not to beat a dead horse but I will anyway. It always pi**es me off when someone says increasing the light thru a lens by +/- 7% improves vision. AR reduces reflections it does not per se improve vision.

[Tallboy]

AR reduces reflections it does not per se improve vision.

So colors seeming brighter and less visual noise to me = improved vision.

Every single +12 or greater lens I've dispensed has felt like it was easier to read with AR.

There is a reason low vision specialists recommend bright lamps for reading. Because it improves vision.

Obviously all of this goes out of the window if the patient can't or won't keep them clean. Greasy AR lenses are significantly worse than a nonporous hard coated lens.

[optical24/7]

Not to beat a dead horse but I will anyway. It always pi**es me off when someone says increasing the light thru a lens by +/- 7% improves vision. AR reduces reflections it does not per se improve vision.

Don, we see by contrast. Write your name on a white sheet of paper with yellow ink, then with black. Of course the black is more legible. just as in the dark/low light conditions we don't see as well. More transmittance = more light hitting the retina. Even though the below paper was sponsored by Big E, it's still a valid assessment.

https://www.essilorusa.com/content/d...activities.pdf

[drk]

Don, we see by contrast. Write your name on a white sheet of paper with yellow ink, then with black. Of course the black is more legible. just as in the dark/low light conditions we don't see as well. More transmittance = more light hitting the retina. Even though the below paper was sponsored by Big E, it's still a valid assessment.

https://www.essilorusa.com/content/d...activities.pdf

Dang I didn't read far enough, 24. Good post.

(Did I call that, or what?)

[drk]

Not to beat a dead horse but I will anyway. It always pi**es me off when someone says increasing the light thru a lens by +/- 7% improves vision. AR reduces reflections it does not per se improve vision.

Not in the "recognition acuity" sense (optotypes on a Snellen chart).

But very arguably in the contrast sensitivity sense.

Which is underrated.

That would be a cool study.

I hope Essilux does one.

And then comes up with a new vision disorder that their lenses cure.

"Dyscontrastopsia" would work.

[Robert Martellaro]

Discussed recently.

http://www.optiboard.com/forums/show...-next-few-days

https://www.2020mag.com/article/is-y...g-stressed-out

Hope this helps,

Robert Martellaro

[Chris Ryser]

Discussed recently.

http://www.optiboard.com/forums/showthread.php/65715-There-will-be-a-rush-of-crazed-AR-coatings-over-the-next-few-days

https://www.2020mag.com/article/is-your-ar-coating-stressed-out

Hope this helps,

Robert Martellaro

It helps for sure...........if you think about it, and remember it.

However this thread was started in Malaysia where I have never been, but knew that it was in a hot/warm geographic area and never even assumed that they could have anything else in sudden temperature changes than going from the heat into the air conditioned house.

So it has been a new version for a theme of "deja vu" like most themes in threads, that come up periodically in a new version.

[Sibirer]

I'm consistently amazed year after year how well modern AR stacks hold up to extreme temperature swings. I see lenses exposed to rapid 100 degree F temperature changes (-30Foutdoors to +70F indoors, etc.) every year and they hold up very well with very few failures on lenses that weren't already damaged.

[Chris Ryser]

I see lenses exposed to rapid 100 degree F temperature changes (-30Foutdoors to +70F indoors, etc.) every year and they hold up very well with very few failures on lenses that weren't already damaged.

Thank you for your post and opinion ...................

How did the few failures you had get damaged prior to exposure to the described rapid temperature changes ?

[Sibirer]

Thank you for your post and opinion ...................

How did the few failures you had get damaged prior to exposure to the described rapid temperature changes ?

Most pre-existing damage was due to deep scratching into the substrate, severe scouring of the top coat, or DEET exposure.

[Robert Martellaro]

I'm consistently amazed year after year how well modern AR stacks hold up to extreme temperature swings. I see lenses exposed to rapid 100 degree F temperature changes (-30Foutdoors to +70F indoors, etc.) every year and they hold up very well with very few failures on lenses that weren't already damaged.

Carl from sci.med.vision? I remember very knowledgable and thoughtful posts. Thank you (and Barry, Mike, Jeff, etc. at SMV) for sharing that knowledge with us in the past.

Please don't be a stranger.

Best regards,

Robert Martellaro

[Chris Ryser]

I'm consistently amazed year after year how well modern AR stacks hold up to extreme temperature swings. I see lenses exposed to rapid 100 degree F temperature changes (-30Foutdoors to +70F indoors, etc.) every year and they hold up very well with very few failures on lenses that weren't already damaged.

Most pre-existing damage was due to deep scratching into the substrate, severe scouring of the top coat, or DEET exposure.

Now I am really wondering what all this scientific talk and knowledge is, about plastic materials contracting or expanding, depending on the temperature and its changes is, when an experienced optician who lives in the middle of ice cold Alaska, says it is not so.

Before knowing anything about glasses, I learned in school why the railways always had this repeating nose when running on their rails. It was the gaps where one rail joined the next to provide a space for expansion or contraction, because of temperature changes.

[hosam]

I Agree with you 👍

[Chris Ryser]

I Agree with you

Thank you hosam ...................

You can not change simple physical laws. If two temperature sensitive, counteracting materials are mechanically joined together, there will be a severe reaction, when suddenly exposed to a temperature reaction.

This has nothing to do with application techniques or sloppy manufacturing.

I have handled many of the highest rating cameras made in my life time, and never seen a cracked AR coating on any of them in over 50 years, and they have seen, and be used from the cold South Pole to the North Pole and all hot spots in between, and never had a cracked AR coating.

............very simple explanation these camera lenses, made in glass got the AR coating which is also glass (SIO2) and have a same type material coating. Perfect combination.

This is also one reason while the sale of AR coatings on glass lenses still flourishes in Europe, where opticians only have to deal with scratched and otherwise damaged coatings, which is abuse of the material.

The use of AR coatings on Polycarbonate and high index, is another question, they are two lens materials that can not be stripped when damaged, as the acids will turn the material milky white.

The only plastic lens material that is easily AR coating stripable if needed, is CR39, and is not affected by the process.

[AndyOptom]

Whoa, real life caught up to me for a bit, and lots of replies when I returned XD

All the feedback is appreciated, and I did check with my local meteorological department's records: apparently, the temperature fluctuation currently is between 10 to 20 degrees Celsius daily, with maximum recorded temperatures of 38 Celsius and minimum of 15 Celsius (during rain).

Truly, it does not seem like a huge variance (with the exception of the thunderstorms), and we've always been hot/humid through the year. I understand the mechanics of this situation, but am wondering if a 10 Celsius variation could really do such damage to an AR stack.