Filters and filtration

[MikeAurelius]

A continuation of the discussion elsewhere.

Some basic information...

There are always good reasons for filters in our daily lives. Grey tints and polarized filters to cut back the sunlight, UV filtered automobile windows to lessen the amount of damage to fabric and vinyl.

In the crafting of art glass, the most well-known is 'didymium'. This has become a generic term over the years for a sodium flare filter that removes the yellow ball of light that occurs when any type of glass that contains sodium (almost all of them) is heated.



The above picture is a bench-mounted art glass torch, burning oxygen-propane at approximately 3800 F. The glass being worked is borosilicate art glass (pyrex). The picture on the left is unfiltered, the picture on the right is filtered through a 3rd generation didymium-variant filter. As you can see, the yellow of the flame is totally removed, leaving only the blue-white flame plume. This allows the glass artist to see the work he's doing inside of the flame, which would otherwise be obscured.

Here's the visible light spectrum of the camera filter being used:



This filter, we've named AUR-40, or simply Dash 40, is a 3rd generation didymium-variant from Schott. Based off the previously available S-8817a ACE glass, this particular filter has a much deeper sodium flare notch, as well as a secondary green/yellow notch. These filters were originally designed for avionics to remove stray distracting colors in the cockpit of commercial and military aircraft.

Here's a color comparison of the previous AUR-92/ACE filter and the new Dash 40 filter:



The lens on the left is the Dash 40, the lens on the right is AUR-92/ACE.

Dash 40 and AUR-92/ACE are good filters for working soft glass (soda/lime). However, when the artist is working borosilicate glass, the amount of heat energy required, as well as the overall size differences in the pieces being worked requires different filtration requirements. To meet these needs, I designed several different filters combining both generic welding filters as well as specialized IR filters.

--more to follow

[Robert_S]

That was a really cool read so far. Thank you.

[Uilleann]

As a matter of course, I would very much like to include in this discussion the actual hard science behind the new glut of expensive "blue" filtering lenses that, on the surface, appears to be the bandwagon of the week.

If there is hard, tested, peer reviewed, reproduce-able science that supports measurable retinopathy in humans directly associated with visible light exposure, I am very interested in the specific frequency or frequencies associated, the specific exposure levels measured, and the environment in which the exposures were observed. I would very much like to see a simple table quantifying frequency, energy level, and duration that is deemed "dangerous".

Apart from this, it is clear that of these new breed of "blue blocking" lenses, that absolutely NONE of them are in fact "virtually clear" at all. This is an important point to be clear on, both for ECPs and patients alike. A "virtually clear" lens is more accurately described as something such as a CR39 or poly blank with a high quality AR such as HiVision, Sapphire or the like. But it is factual to remember every single one of these blue blocking lenses will attenuate visible light, and "tint" the users vision to a greater or lesser degree. The only question at that point is to ask your pt how much they feel they could tolerate in their given use environment.

Discuss away-

[Uilleann]

Any discussion surrounding the hard science of the latest "blue blocking" lenses? Anything?

Just crickets...?

[ml43]

Any discussion surrounding the hard science of the latest "blue blocking" lenses? Anything?

Just crickets...?

do you want more clinical testing?
or material science and optics testing/research?

material science and optics I can try dig a bit. Have a few phd professors I can bug over the next few months.

it's quite interesting to see chemistry, physics, and optics all coming together.

[Uilleann]

More the clinical side really - and the specifics of how - indeed, IF - retinal damage in humans can be directly linked to exposure to quantifiable amounts of specific wavelengths of visible light in the blue and violet portions of the EM spectrum. If so, what are the particular frequencies (assuming its some sort of range), and the particular level of exposure shown to cause harm.

So far, we've seen an entire bevy of lens makers and labs jumping on the vague blue light bandwagon - but absolutely no consensus in the medical community to the specifics of exactly what or how much may or may not be harmful in some broad and general way. It is entirely convenient today to try and pin blame for an as yet poorly defined problem on E this and E that - perhaps too convenient. And more than a few of us remain highly skeptical. If indeed there is so much potential damage to be caused by tiny electronic lights - vs the amount of exposure we get from say, doing to an IMAX movie, or a concert with ultra bright LED stage lighting, or even mere seconds of full spectrum sunlight, one would hope and certainly expect that there are better ways of quantifying the damage potential in highly testable and repeatable ways.

[ml43]

More the clinical side really - and the specifics of how - indeed, IF - retinal damage in humans can be directly linked to exposure to quantifiable amounts of specific wavelengths of visible light in the blue and violet portions of the EM spectrum. If so, what are the particular frequencies (assuming its some sort of range), and the particular level of exposure shown to cause harm.

So far, we've seen an entire bevy of lens makers and labs jumping on the vague blue light bandwagon - but absolutely no consensus in the medical community to the specifics of exactly what or how much may or may not be harmful in some broad and general way. It is entirely convenient today to try and pin blame for an as yet poorly defined problem on E this and E that - perhaps too convenient. And more than a few of us remain highly skeptical. If indeed there is so much potential damage to be caused by tiny electronic lights - vs the amount of exposure we get from say, doing to an IMAX movie, or a concert with ultra bright LED stage lighting, or even mere seconds of full spectrum sunlight, one would hope and certainly
expect that there are better ways of quantifying the damage potential in highly testable and repeatable ways.

totally agree from a medical/clinical stand point.

One thing I will point out and throw out there is consensus.
I understand it is a somewhat norm in the medical field to appeal to authority and consensus.
But, consensus science is not science.

I think it would serve your purpose in a more efficient way to find someone that can prove that violet/blue light has no relation to AMD.

[Dr. Bill Stacy]

[QUOTE=MikeAurelius;512029]

There are always good reasons for filters in our daily lives. Grey tints and polarized filters to cut back the sunlight, UV filtered automobile windows to lessen the amount of damage to fabric and vinyl.

In the crafting of art glass, the most well-known is 'didymium'. This has become a generic term over the years for a sodium flare filter that removes the yellow ball of light that occurs when any type of glass that contains sodium (almost all of them).

Humans have been looking at glowing embers for thousands if not millions of years. And then somebody comes along and thinks the eye cannot handle the yellow, orange, red and infrared wavelengths, so we must protect them from those wavelengths.

So along come some enterprising O types that sell the public on the idea that they need protection.

But you know the rest of this story. It has to do with snake oil.

[ml43]

I'm pretty sure the miscommunication between you two is not the approach but the application.

mike makes lenses/filters for specific purposes

your coating is just like every other blue light coating in the fact that it is marketed at all audiences as a preventative health item rather than as a specific application. kind of like vitamins vs supplements for lack of a better analogy.

and for the record, your coating can be ordered through any decent coating lab, you just need to know how to order it. pm me for details if you want.

[Chris Ryser]

Humans have been looking at glowing embers for thousands if not millions of years. And then somebody comes along and thinks the eye cannot handle the yellow, orange, red and infrared wavelengths, so we must protect them from those wavelengths.

So along come some enterprising O types that sell the public on the idea that they need protection.

But you know the rest of this story. It has to do with snake oil.

Over the years in the century where CR39 lenses was the in thing we sold thousands of bottles for UV treatments. My believe was that a UV treatment should cover the invisible spectrum right up to 400nm.
The theories on UV protection where, and still are, that the exposure range of 352 nm to 400 nm was the one that would promote and initiate cataracts and othe medical problems.

This ended in a lens that had a slight yellowish apearance which could be changed by tinting over it to make it cosmetically more apealing.

However the majority of optical retailers adopted the idea that a lens should be a clear one and still filter out all the UV that was needed to give full protection and so did all the labs.

So the majority of UV protective lenses sold on this continent where clear, but only absorbed UV to 382 nm and not the required 400 nm, which is just about half way between the 360 and 400 nm.

These days optical retailers are selling Polycarbonate lenses which are claimed to be 100 percent UV absorbant on every ad I read about lenses made from that material. However they are clear and do not have the needed yellowish tinge to make it to 400nm.

I own one of the fanciest spectrometers and have never even put a polycarbonate lens through it. So I went on the google and tried to find just one spectrometer transmission result/graph on polycarbonate lenses……...and there is none. I am pretty good at getting answers as I usually ask the questions in multiple ways.

Here we are discussing protection of the eyes against visible blue light, and it looks that we might totally ignore the possibility of not even protecting the Eyes of a real exposure to a total 100 % range of the UV spectrum.

[MikeAurelius]

[QUOTE=Dr. Bill Stacy;512325]

There are always good reasons for filters in our daily lives. Grey tints and polarized filters to cut back the sunlight, UV filtered automobile windows to lessen the amount of damage to fabric and vinyl.

In the crafting of art glass, the most well-known is 'didymium'. This has become a generic term over the years for a sodium flare filter that removes the yellow ball of light that occurs when any type of glass that contains sodium (almost all of them).

Humans have been looking at glowing embers for thousands if not millions of years. And then somebody comes along and thinks the eye cannot handle the yellow, orange, red and infrared wavelengths, so we must protect them from those wavelengths.

So along come some enterprising O types that sell the public on the idea that they need protection.

But you know the rest of this story. It has to do with snake oil.

American Optical invented the original didymium lens in the 1920's for companies that were making vacuum tubes, so that the machine operators could see through the glaring ball of light (sodium flare) to ensure that the end of the tube was properly sealed before the electrical leads were attached to the base.

Sodium flare is not dangerous to the eye. I've never said it was, nor will I ever say it. It is, however, distracting, and an impediment to viewing inside of a flame.

[Craig]

Mike,
These are your best posts imho.
Keep it up.

[RT]

If there is hard, tested, peer reviewed, reproduce-able science that supports measurable retinopathy in humans directly associated with visible light exposure, I am very interested in the specific frequency or frequencies associated, the specific exposure levels measured, and the environment in which the exposures were observed. I would very much like to see a simple table quantifying frequency, energy level, and duration that is deemed "dangerous".

Not sure if it is in exactly the form that you've demanded, but ANSI Z87.1 has long included a blue light hazard weighting function. The blue light hazard weighting function was originally published by ACGIH (American Conference of Governmental Industrial Hygienists). This shows the most damaging wavelengths to be at 435 and 440 nm. The 2015 revision (you own the latest, right?) references 2008 ACGIH data. The 2003 revision of ANSI Z87.1 references the 1982 blue light hazard information.

[RT]

My believe was that a UV treatment should cover the invisible spectrum right up to 400nm

ISO Standard 13666 says: "For the purposes of this International Standard regarding spectacle lenses, the upper limit for UV-A is 380 nm. This limit is also specified in ISO 20473."

ANSI Z80.1 also defines the upper limit of UV-A as 380 nm.

[MikeAurelius]

Mike,
These are your best posts imho.
Keep it up.

Thanks, I've been working on the next installment, covering IR and high intensity visible light. I've got to convert a couple of graphs from a transparent background to a white background, vBulletin is insisting that a transparent background is actually black LOL, which makes the graphs almost impossible to read.

[MikeAurelius]

Didymium started out as a filter for the ladies who were sealing vacuum tubes back in the 20's and 30's as the 'radio era' exploded and all sorts and varieties of tubes were needed. It was through the name "glass blowers" filter that all sorts of deviations of the correct use of the filter came to be, as a misnomer some people still call it that and use it for traditional glassblowing (which it should not be used for btw).

AO (American Optical) was the originator of the glass type, and it was first made in their facility in Southbridge MA.

Fast forward to the 1960's, Schott took over the manufacture of the product as AO phased out its glass making production lines and moved towards making frames exclusively.

Schott refined the material substantially from AO's formulation, and did large scale strip melts of the glass through the 1980's. A typical strip was about 7" across and 9-10 mm thick and melted in a continuous strip, cut to length during the annealing process.

The glass itself was melted in a continuous batch furnace and started life as clear crown glass, with an index of refraction of 1.523. Traces of arsenic, potassium, are in the glass to stabilize the index, while neo- and praeso- dymium are added (the exact mixture remains a protected "secret"). The strip was repressed into a variety of shapes by United Lens Company of Southbridge MA (across the street from the AO facility).

In the 1980's Schott developed an amethyst (blue) shaded glass filter for the aviation industry because of the increase in video screens in the cockpits. This filter was required to have several additional filter notches along with the classic sodium flare. Schott approached Aura in early 1991 to see if we were interested in the glass for ophthalmic applications, and did a short run test melt in several ophthalmic lens shapes. The rest, as they say is history.

The original ACE glass was a lanthinum based crown, with an index of refraction of 1.572. There are problems with lanthinum based glass lenses, most notably staining during processing. Around 2001, Schott reformulated the glass and moved it back to a clear crown base, but kept the index stabilized at 1.572. There is barium, potassium, and a few other "rare earths" in the glass mixture along with the neo- and praeso- dymium materials. Again, the exact composition is a trade secret.

Hoya makes a similar glass type, but it is available only in finished polished flats, 2 mm thick. Corning France used to make an "enhanced" version of the glass with additional IR filtering components, but stopped production when the price of the raw materials (due to Chinese embargoes of the rare earths became too expensive).

Schott moved the production of all of their glass to Germany in the mid- 2000's, and then sold the production facility to an Italian company (Barberini). The facility remains in Germany, with Schott overseeing the production, but all sales of all products manufactured in the facility are made through the Barberini.

The last batch of ACE glass was manufactured approximately 2007, and as far as I am aware, there are no current plans in place for the next melt. Currently, there is very little ACE glass left and Barberini requires an order for 3 metric tons (which is approximately 15 years worth of glass). The best that myself and three other companies have been able to come up with is a quantity of 1 metric tons. Smaller pot melts cannot be made with this specific glass type.

That's probably far more history than you wanted to know, and probably not enough chemical detail, but that's what happens when trade secrets are involved.

The current material is a Schott filter, again made for the avionics industry, and has an even better sodium flare notch, and we refer to it as a 3rd gen didymium.

[MikeAurelius]

For those that are into technical information, here are the chemical constituents of the various glass types made by Schott that relate to hot glass working.

I've pulled the MSDS on the didymium glass types from Schott, here are the percentages as listed. Note that the OSHA does not require exact percentages, allowing for trade secrets, ranges are permitted.


S-8304 (medium green) didymium (discontinued ~1975)


Silica > 51%
Sodium Oxide 11 - 20%
Zinc Oxide 1 - 10%
Calcium Oxide 1 - 10%
Aluminum Oxide 1 - 10%
Arsenic Trioxide < 1%
Neodymium Oxide 1 - 10%


S-8305 (dark green) didymium (discontinued ~1975)


Silica > 51%
Sodium Oxide 11 - 20%
Zinc Oxide 1 - 10%
Aluminum Oxide 1 - 10%
Arsenic Trioxide < 1%
Neodymium Oxide 1 - 10%


S-8801 "rose" didymium


Silica > 51%
Sodium Oxide 11 -20%
Potassium Oxide 1 - 10%
Zinc Oxide < 1%
Aluminum Oxide 1 - 10%
Neodymium Oxide 1 - 10%


S-8807 A.C.E. (originial formulation)


Silica > 51%
Boron Oxide 1 - 10%
Sodium Oxide 11 - 20%
Zinc Oxide 1 - 10%
Neodymium Oxide 11 - 20%
Cerium Oxide < 1%
Copper Oxide < 1%


For comparison, here are the formulations for clear crown ophthalmic glass:


S-1 crown


Silica > 51%
Sodium Oxide 1 - 10%
Potassium Oxide 1 - 10%
Zinc Oxide 1 - 10%
Calcium Oxide 1 - 10%
Aluminum Oxide 1 - 10%
Titanium Oxide < 1%
Arsenic Trioxide < 1%
Antinomy Trioxide < 1%


S-3 crown (S-3 crown was developed to optimize the glass for chemical bath strengthening)


Silica > 51%
Boron Oxide 1 - 10%
Sodium Oxide 1 - 10%
Potassium Oxide 1 - 10%
Zinc Oxide 11 - 20%
Aluminum Oxide 1 - 10%
Titanium Oxide < 1%
Arsenic Trioxide < 1%
Antinomy Trioxide < 1%

[MikeAurelius]

Actual UV generation from heat alone does not start until temperatures reach approximately 4500 degrees F. However, some metals and some minerals do generate UV, but the threshold has always been below that where serious protection is needed.


All of the eyewear sold that is made from glass protects the eye from the hazardous UV, which is generally accepted to be 320 nanometers and below. The range of 320 nm to 400 nm is still UV, but the amount of damage done there is far less than the lower range. Basic ACE glass stops filtering at about 350 nm. But, keep in mind that this is a soft glass filter, and at soft glass temperatures, the amount of UV generated has been shown to be negligible.


A borosilicate filter, such as our AGW-203, a shade 3 equivalent, starts passing UV at approximately 380 nm and at 400 nm passes about a 0.5%. Higher shade numbers pass about the same amount of UV.


The point here, that needs to be made, is that UV **IS NOT** and should not be your main concern. IR, infrared, heat energy is and always should be your concern.


Plain ACE glass alone passes approximately 45% of IR between 750 nm and 900 nm and nearly 85% of IR out beyond 900 nm, which is the hazardous portion of the IR spectrum. This is the main reason we have never recommended plain ACE glass for anyone working with borosilicate glass.


A borosilicate filter, such as our AGW-203, a shade 3 equivalent, passes an average of 2% of IR between 750 nm and 900 nm, and less than 0.25% beyond 900 nm. This is the minimum we recommend for working with color borosilicate glass.


In my opinion, the reason the UV is a concerning issue from the OD/MD standpoint is that there is documented proof that outdoors sun exposure does over time damage your eyes. However, you are not outside (usually) when working glass, so it really isn't the issue that it is made out to be in these circumstances.


IR damage is not really taught in OD/MD school, nor is specialized filtration requirements, so many times doctors and optical dispensers don't have the knowledge base to work off of for proper selection of lenses. This is how "didymium" came to be called the 'glass blowers' filter, and even after 30+ years of us trying to educate the optical profession, we still get dispensers and doctors trying to provide didymium lenses to people who do traditional glass blowing. "Well, it's called a glass blowers filter..." *sigh*

[AngeHamm]

Apart from this, it is clear that of these new breed of "blue blocking" lenses, that absolutely NONE of them are in fact "virtually clear" at all. This is an important point to be clear on, both for ECPs and patients alike. A "virtually clear" lens is more accurately described as something such as a CR39 or poly blank with a high quality AR such as HiVision, Sapphire or the like. But it is factual to remember every single one of these blue blocking lenses will attenuate visible light, and "tint" the users vision to a greater or lesser degree. The only question at that point is to ask your pt how much they feel they could tolerate in their given use environment.

Untrue. Mitsui's TheraBlue is as visually clear as an unactivated Transitions lens. Debate the merits of HEV-blocking lenses all you wish (it's a legitimate discussion), but this particular statement is patently false.

[Judy Canty]

Deleted.

[Uilleann]

Sorry - wrong. Unless you define "virtually clear" as anything from a 15-30% filter. Transitions (or any photochromic lens, in any material I've ever seen) lenses aren't clear either of course, and neither is this latest in a long line of "blue light killing" lens.

Regardless of perceptions of "clear", I'm still interested in much more information from studies showing repeatable and incontrovertible scientific evidence directly linking visible blue light to human retinopathy. Will look with greater scrutiny at the ACGIH site to see what they have to say about "hazards" associated with blue light. At a glance, it appears only IR radiation is of any real concern to them, but it warrants further looking on my part.

[Dr. Bill Stacy]

Wonder why Judy used a tinted polycarb lens in this comparson?

[Judy Canty]

Deleted.

[AngeHamm]

Sorry - wrong. Unless you define "virtually clear" as anything from a 15-30% filter. Transitions lenses aren't clear either of course, and neither is this latest in a long line of "blue light killing" lens.

I'm getting really tired of you calling me a liar, buddy. I've held this product in my hands. Have you? How about a certain level of professional collegiality on this professional optics board?

I don't work for Judy. I don't sell this lens. My office doesn't even provide it to patients at this time. I have absolutely no financial stake in whether or not anyone buys this product. I have posted nothing but my own extremely, extremely well-informed, skeptical, and experienced perspectives on a product that many other professionals are interested in.

You can disagree with the medical need for this product all you want. I'm not convinced myself, though the doctor who signs my checks is, so I am exploring all options, as is my professional duty. But when I say "This lens is virtually clear," and you say "No it isn't," you are either calling me a liar or an incompetent. And I've got news for you: the one who's coming across as unprofessional here isn't me.

[MikeAurelius]

Attachment 12275

Judy, I'm assuming the central CR-39 lens is an as-is lens, no additional coatings, etc.

I can see a visible difference in color, appears to be very very very slightly grey in color, compared to the CR-39, about mid-point between the CR-39 and the SunSensors lens. I believe *this* is what the fuss is about. It is noticeable when compared against a white background, but I do doubt that the average consumer would notice the difference.

Now, you posted this:



on the original thread, I went back and re-read it, comparing the press release to the picture. I call your attention to the press release, and a couple of things pop out at me immediately:

1) The press release claims 'it is not a coating like some other products...'. If that's the case, why the clear edge all the way around the lens, visibly showing a comparable color and reflection as the untreated CR-39 lens.

2) The press release claims '...does not have a purple or blue reflective color...' actually, to my eyes, it looks blue/green.

I'll also note that the press release also states "near clear" and "almost clear"; this flies in the face of your and others' statements that it is clear. It isn't.