Why doesn't the CR-39 monomer have UV protection? Does it's chemical makeup not provide any UV inhibitors? If not, then what chemical or material in poly and high-index provide UV protection
Why doesn't the CR-39 monomer have UV protection? Does it's chemical makeup not provide any UV inhibitors? If not, then what chemical or material in poly and high-index provide UV protection
CR-39 does in fact block UV light, but only up to 360nm. I believe the big reason that CR-39 does not block up to 400nm by itself is the UV filter at that point would cause the lens to be tinted light yellow, which is cosmetically unappealing.
Rolandclaur, you ask a complex question.
U V protection is obtained by blocking the UV light through a certain wave length. Polycarbonate does block a large percentage of UV but not all and needs a UV blocking added to give great UV proctection (to 400nm). CR-39 does not naturally block UV but to a limited degree (approx. 360nm I believe). Each monomer has different chemical properties. I do not have enought time or energy to go into each chemical that I either know or can find the information about, however the manufacturer supplying the lenses will furnish the information regarding the amount of UV blocking provided in the lens you are purchasing. Many lens manufacturing/distributing companies do not know all of the methods used in the production of their lenses, as they purchase the monomer, (very few actually make the lens and the material). The material (monomer) manufacturer recommends the best method of adding UV protection to their material, and the company will then produce it in this manner. Your lab gets these lenses and supplies them to the optical retailer (which I assume you are).
It is not quite as complicated as "How do build the rockets for the space shuttle", but it is a totally different area that you do not need to know a lot of detail about.
I got a question, is the amount of UV a cr-39 lens let in really dangerous at all?
UV-C is extremely harmfull but is mostly absorbed by our atmosphere UV-B is blocked by cr-39 up to, like awtech and jedi said, approx 360 nm. The range for UV-B is approx 275-300nm. I believe that UV-A (330nm-400nm) is considered the least harmfull and even most of that is absorbed by the CR-39 monomer. ANSI standards uses 380nm as the end of the UV spectrum. So it looks like much of the harmful UV radiation is absorbed by the CR-39 monomer but I still recomend it.Originally Posted by For-Life
I suppose I did ask a very complex question.. I guess when it comes down to it.. I was just concerned with its UV blocking properities that would safely block the proper amount for the wearer..
UV has to be done properly..................
CR39 used to go yellow in the 1970's because of UV influence. Then lens manufacturers started to add clear UV to the base material so that the cured lens would not yellow anymore.
As a next step some of them came up with CR39 that would absorb all the way to 400nm.
This required a double size lens stock , one in regular andf one in UV treated lenses.
As next step the UV solution came on the market and you could do the treatment in office, this killed the sales of finished UV lenses.
Read about the whole story at : http://optochemicals.com/prism_article.htm
Chris touched on the issue with plastics. The high energy content of UV radiation can break certain chemical bonds in plastics, causing them to absorb more light at lower wavelengths (the blue end of the spectrum) -- which results in "yellowing." UV inhibitors or UV stabilizers are added to the monomer in order to prevent this degradation. These chemical additives essentially absorb the UV radiation in order to prevent it from being absorbed by the monomer (which would otherwise lead to discoloration).
Consequently, plastic materials in general absorb a significant amount of UV radiation (basic hard resin from many manufacturers, for instance, absorb 100% of UVB and up to 90% or more of UVA, without additional treatments). Moreover, the chemical bonds in many high-index materials are even more susceptible to the effects of UV radiation, placing an even greater importance on the use of UV inhibitors (these materials will often absorb 100% of both UVB and UVA).
Darryl J. Meister, ABOM
Darryl,..........................
Darryl, good explanation.
Why dont you copy all those worded postings on your website, and you will have pages an pages to show. Furthermore, congratulations on your website it just got rated by Alexa and is no mor e NO DATA website.
One must also define "dangerous" while macular degeneration, skin cancer and catarac are all "caused by UV" remember we have a lot of emetropes, low myopes and low hyperopes running around with no spectacles at all. Are they in "danger." Did 100% of people get any of the above conditions when we largely worked and plaid outside, of course not.
In fact in today's inside job, couch potato, video-gamed out world, all of the above conditions should be practically wiped out like diptheria, and polio. In this case just by life styles.
Most of today's generation won't even know what "seasons in the Sun" were.
Chip
I do not believe that UVA has been linked to macular degeneration, probably because the crystalline lens filters this spectrum of light before reaching the retina.
I agree that the risks to the eyes from damage due to UV exposure is overstated for those living in northern latitudes and at sea level, and should only be a concern for those who spend most of their day in the sun and live at mid and southern latitudes.
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.
I hope that you have heard that the ozone layer has been eliminated over a large portion of North America over the last few years.
UV damage has increased in every way.....from skin cancer to eye problems...........and this is NOT overstated, ........these are facts.
I would suggest you talk to some oncologist's or dermatologist's in your
neighborhood to get the real facts facts.
Eliminated? That would mean that the animals and crops would turn into dust. Maybe you are exaggerating to make a point and yet you speak of getting "real facts". In that case I must ask for references for the above statement. My first page Google search came up with this...
What the Data Shows
Figure 015-1 shows that total ozone measurements from the four monitoring stations declined during the period 1979 to 1993, after which they leveled off, though at a level lower than pre-1980. The large annual variation shown in each of the four cities is a result of ozone transport processes that cause increased levels in the winter and spring and lower ozone levels in the summer and fall at these latitudes
According to the most recent international scientific assessment, the global-average total column ozone during the period 1997 to 2001 was about 3 percent below average pre-1980 values (WMO, 2003). Trends over North America reflect this global phenomenon.
http://epa.gov/ncea/ROEIndicators/pd...AMER_FINAL.pdf
Ultraviolet light exposure and lens opacities: the Beaver Dam Eye Study KJ Cruickshanks, BE Klein and R Klein
Department of Ophthalmology, University of Wisconsin, Madison.
OBJECTIVES. Exposure to sunlight may be a risk factor for the development of cataract. The relationships between exposure to sunlight and to the ultraviolet-B (UVB) component of light and the prevalence of lens opacities were examined in the Beaver Dam Eye Study. METHODS. Persons 43 to 84 years of age residing in Beaver Dam, Wisconsin, were examined using standardized photographic assessments of lens opacities. A questionnaire about medical history and exposure to light was administered. RESULTS. After adjusting for other risk factors, men who had higher levels of average annual ambient UVB light were 1.36 times more likely to have more severe cortical opacities than men with lower levels. However, UVB exposure was not found to be associated with nuclear sclerosis or posterior subcapsular opacities in men. Moreover, no associations with UVB exposure were found for women, who were less likely to be exposed to UVB. CONCLUSIONS: Exposure to UVB light may be associated with the severity of cortical opacities in men. However, the lack of an association in women, the group more likely to have cortical opacities, suggests that other factors may be more important in the pathogenesis of lens opacities.
http://www.ajph.org/cgi/content/abstract/82/12/1658
I would ask an ophthalmologist about damage to the eyes from light exposure before I would ask a dermatologist. To be sure, the skin around the eyes receive protection from UVB blocking lenses, anecdotal evidence suggests that the cancer appears more commonly towards the middle and end of the nose, an area not protected by eyeglasses.
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.
According to EPA...........................
I would ask an ophthalmologist about damage to the eyes from light exposure before I would ask a dermatologist.
http://www.epa.gov/docs/ozone/science/process.html
The Process of Ozone Depletion
Since ozone filters out harmful UVB radiation, less ozone means higher UVB levels at the surface. The more the depletion, the larger the increase in incoming UVB. UVB has been linked to skin cancer, cataracts, damage to materials like plastics, and harm to certain crops and marine organisms. Although some UVB reaches the surface even without ozone depletion, its harmful effects will increase as a result of this problem.
Last edited by Chris Ryser; 08-10-2005 at 11:44 AM.
I am still wondering why discussions on UV protection and or damage on this forum always dye off very fast...............while a thread about drilling holes can go forever.
Are opticians not interested in the protection of their customers well being? Or do they know it all?
maybe it has to do with the fact that if one wants UV treated cr-39 lenses, all one has to do is put it in UV treatment for a minute or so. Personally I care very much for the well being of my patients, so much so that over 75% of what I sell is poly. Everything else gets treated even if they didn't pay for it, unless of course it is already UV blocking.
Opticiansfriend.com guy.
That's very noble of you. Maybe you should give away polarized lenses instead, lest you have blood on your hands.
http://www.youngeroptics.com/news/news.html
I would rather have cataract surgery a couple of years sooner than average (if I live that long) than to be reduced to a red stain on the windshield of a locomotive.
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.
Did you know that a minute or so........will give you a UV treatment that will not absorb and protect anymore after a couple of weeks?
No I didn't. That's interesting. So you are telling me that the UV treatment will eventually lose its strength? What I was getting at was that it's relatively easy to treat a lens vs drilling.
Opticiansfriend.com guy.
???? What are you talking about? Why should I give away polarized lenses?? I sell poly almost exclusively in a variety of types including polarized. If they need sunglasses, I go with polarized anyway. I do this already. Seriously, what are you talking about??? Are you comparing a lens treatment that costs pennies to treat per lens (when the patient wants say reading glasses in cr-39) with giving away polarized lenses? How about this: Why don't you wear UV protection and possibly delay the onset of a cataract to begin with? So you don't care about your patients enough to provide them with some type of UV protection. Did you know that the eye lids are the thinnest in terms of skin thickness and hence the most susceptible to skin cancer than any other part of the body? I would love to hear your explanation.
Opticiansfriend.com guy.
I personally don't give the patients a choice in whether they want UV or not. It shouldn't be a choice.
Tine too short.........................
Read the whole story at: http://optochemicals.com/prism_article.htm
.................UV SOLUTIONS FOR FAST TREATMENTS. (NO TIME DO WAIT)
The market is flooded today with solutions that are supposed to do the job in a short time. There are some products on the market now that claim a 60 second immersion time in the hot solution will do the trick.
A lot of laboratories claim that they do not have the time for long treatments. As long as the lens measures the proper absorption when the job gets out the door, everything is OK. Never mind what happens in three months from now.
The lens takes time to open its pores under heat. The UV absorber takes time to penetrate the lens surface, and it takes its time to re crystallize.
What happens when treating with the short time products?
The lens surface has no time to open its pores because of the short time span. The UV absorbing chemicals can only deposit themselves on the surface. They cling to the surface as well as they manage. When checked with a UV Meter or Spectrometer these lenses will show a good absorption level, but ........................................................
We use a regular non-gimmicky UV treatment. That's very good to know. I am glad you told me.
Opticiansfriend.com guy.
i've always been taught in my finishing lab to submerge the CR-39 for at least 15 to 20 minutes to maximize absorption of the UV dye into the monomer. Looks like Chris elaborated on why!!
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