Evidently, clear UV-absorbing dyes don't protect above the 385nm wavelength.
Do these dyes become more effective with age? Specifically, do they eventually absorb the entire UV range -- through 400nm?
Evidently, clear UV-absorbing dyes don't protect above the 385nm wavelength.
Do these dyes become more effective with age? Specifically, do they eventually absorb the entire UV range -- through 400nm?
The Real Facts on UV......................
Being one of the first manufacturers of UV dyes (1983) I consider myself an expert in this field and can prove any statement I make on this subject.Originally Posted by chris_the_newbie
Clear UV solutions
Clear UV dyes sold to labs and optical shops absorb UV rays up to 383nm to 385nm.
They will never improve with age and will never protect up to 400nm
UV meters sold by some companies pushing clear UV are adjusted to read 100% at 382nm and NOT at 400nm
One minute UV treatments (as used by Lenscrafters)
These treatments will not penetrate the lens surface (not enough time under heat) and only adhere to the surface and nor penetrate into the lens pores.
As UV solutions are made with a chemical called "benzopheeone" which is soluble in alcohols, it will come off when using the standard type lens cleaners which contain at leat 30% isopropyl alcohol.
Lenses used and treated with one minute UV treatments show reduced or ZERO absorbtion within weeks of purchase by customers.
Many Optical Laboratories want to save time and do use the 1 minute treatments which will read full 100 percent absorbtion at delivery and nothing a few weeks down the road.
The only way to go:
As 400nm is at the edge of visible light. A properly done UV absorbing treatment does have a yellowish tinge in appearance to give the full value of absorbtion and protection 400nm. This treatment will get better and stronger with time. The lenses can be tinted with a light shade to hide the yellowish tinge.
Polycarbonate Lenses are the only lenses that all contain a totally clear UV that absorbs to a full 400nm in every lens you purchase.
Conclusion:
The optical wholesale and retail market has been selling and making money with UV products that do not supply what they promise and many hundred of thousands of patients are under the impression that they are protected against UV interference and while they are not protected at all.
Some of the largest dye manufacturers are totally misleading the optical trade in their advertising on UV absorbance and testing. Everything going on an optical prescription lens becomes part of a "device" and falls under FDA jurisdiction and control.
In order to get around FDA involvment one just marks on the product label "for industrial use"
There have been TV shows (60 Minutes) and many others exposing ineffective UV protection sold for good money be the optical retail trade.
You can read all about it at: http://optochemicals.com/prism_article.htm
Does a CR-39 lens with a 400nm UV treatment end up with the same abbe value as a standard polycarbonate lens? If so, CR-39 has no advantage over polycarbonate, right?
Looks like Abbe value has nothing to do with UV absorbtion between CR39 and Polycarb/
David Wilson on Optiboard posted
11-13-2002, 05:07 AM
The eye has relatively high axial chromatic aberration (between 1 and 2 dioptres, depending on the wavelength of red and violet that you use). However, spectacle wearers are not troubled by axial chromatic aberration. because the ye's own chromatic aberration is greater, they are affected by transverse chromatic aberration (TCA). This is the chromatic aberration created by the the prismatic effect at the periphery of a lens for excentric gaze. TCA is not noticed (according to Jalie) below 0.1 primn dioptre of TCA. The formula for TCA is cF/V. Where c is the distance from the OC in centimetres , F is lens power and V is the Abbe number. According to Torgersen, acuity is not affected until TCA reaches 0.16 prism dioptres and then it drops by one line on the Snellen chart.
Abbe number and TCA is overstated as a problem for spec wearers. It is only a consideration for powers of more than +/-4D and then only at the edge of the lens. As a +6.75D hyperope (with a +1.5D add) wearing lenses of Abbe 36, I can say that, if well fitted, Abbe should not be a problem for most spectacle wearers, especially those below +/-4D. Torgersen and Jalie provide formal evidence of my anecdotal experience.
I hope this is of some use, Edgely.
Regards
David
Jo you are right. The skin takes the biggest burn damge at 324nm, conjuntivities sunburn on eyelids and so forth as results. UV b in the range of 270nm to 365nm creates immediate burn damages.
Up to 1980 every plastic lens would yellow within 2 years and looked real ugly after 3 years of wearing. All due to drying and UV damage.
At that time all lens manyfacturers added a clear UV absorber to the monomer before casting the lenses. This was not to protect your eyes but to prevent the lenses from yellowing.
As added benefit we now have plastic lenses that fully absorb UV B from 270nm to 365nm and therefore protect eyes from the immediate damages of UV radiation.
Long Term UV Damage, (needs protection years before it happens)
Long term UV damage is created by UV exposure from 360nm to 400nm.
As the lenses already absorb to 360nm you need to cover the UV B area from 360 to 400nm which is one of the culprits of initiating cataracts and many other medical eye conditions.
Many opticians are of the believe that by selling a clear UV solution they have protected the patient and made some money doing it.
As just about all clear UV solutions stop absorbing at 382nm you cover only half the distance from 360nm to 400nm. You actually unknowingly, because of false advertising by manufacturers underprotect your patient by close to 50% of what you are supposed to do, by not giving them the full protection for long term damage.
By using a UV treatment that covers all the way to 400nm you are giving your patients what they expect from you. Furthermore by properly explaining UV B long term damage you can make an extra sale just about to anybody purchasing glasses the first time and everytime thereafter.
I think that with the craze about AR coatings, the beneficial properly done UV absorbing treatment has been neglected by the optical trade.
Any lens material that is tint able can be treated in a UV solution in your lab, house, backyard and so forth.
Many brands on the market. Just dont buy any clear UV's and any 1 minute treatments. The longer in the solution the better. You can find full information on UV on my website.
If you take a CR-39 lens that has been treated with a clear UV dye, and you give it a yellow tint ... does it provide UV 400 protection?
(Obviously, anyone who has a choice should demand a UV 400 treatment in the first place.)
Chris,
I'll use Nikon as my example but I'm sure many of the majors make the same claims.
Nikon claims that NL5, NL4, NL3 all protect to 400nm.
DX-2 and NL1 proctect to 365nm. From what I have seen the 3 former lenses do not exihibit any yellow hues, they all seems perfectly clear. Is the yellowing subtle on these material or is the "data" not all there?
Quote from an online textbook:
The appearance of a transparent object is dependent upon what color(s) of light is/are incident upon the object and what color(s) of light is/are transmitted through the object.
I think the part in bold might have something to do with the answer to your question.
I'm surprised Chris Ryser hasn't spoken to this point yet but let me give it a shot.
It's possible to add coloring dyes (blue for example) to balance out the yellowness imparted by the UV dye. It doesn't eliminate the yellow but rather shifts the transmitted color to grey. Of course the liability of such an approach is that the total transmission is reduced.
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