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[Fwd: Re: UV protection needed for glass eyeglass lenses?]



Jane & others with or anticipating glasses:
(Isn't this all of us as we get older?)

It seems that I am back in a state of grace as far as our Phys-L e-mail
symbiont is concerned so here are my responses to Jane Jackson on UV
coatings, etc.:

+=================================+=================================+

I've just talked to Larry Tankersley and he confirmed what I thought I had
known from past studies on the subject of UV attenuation and UV
protective coatings.

The best information that we have is as follows:
1) plain old ordinary optical glass cuts off at about 350nm;
2) regular plastic lens material cuts off at about 370nm;
(We're not aware of any differences in so called
"thin lens" or high density optical plastic.)
3) coated lens seem to cut off at about 390nm.

Since what you save by buying the coating is only the stuff between 370
and 390nm which is so soft it shouldn't hurt you, it would seem that
coatings are just another expense that brings very little improvement to
the problem.

While glass lenses are certainly heavier, they do have the added feature
of being MUCH more scratch resistant. If you were to get plastic lenses
(high density or regular), scratch resistant coatings are certainly worth
the expense. Personally, because I tend to get whatever lenses I have
scratched, I find the "lens insurance" well worth the money. After about
11 months, I just get myself a new set of lenses from the insurance. The
glasses providers not only don't mind this, they even recommended it.

On the subject of anti-glare or anti-reflective coatings, opticians almost
always recommend them (at between $35 to $70). I believe that an argument
could be made that being "anti-reflective" implies that the maximum light
is transmitted. Since I am almost never in such low light settings and at
the same time trying to do close-up work, i think that these coatings are
again an unnecessary expense. They do have a great cosmetic value,
especially for those that are very near-sighted.

Also, if no astigmatic correction were needed, the very cheap ($22.00 for
a set of 3 pair from Sam's Club) over the counter plastic lens glasses in
your prescription will do fine. (They are readily available to the
nearest 0.25 diopter.) I like the ability of "prepositioning" pairs of
glasses at several places (car, office, lab, camping back pack, etc.).
While I can still read a book at 20 ft, I have essentially no
accommodation left and cannot read even larger print closer than 3 ft.
So for me, not only can I not get along without glasses in the near
distance, I find them cheap general eye protection.

I hope this is of some help.

+=================================+

On Mon, 20 Nov 2000, Jane Jackson wrote:

I have 2 questions (especially since I've been out of the classroom for
years and haven't kept up on optics - I need quick answers):
1) Since the lenses will be glass, and hence offer some UV protection, is
there any value in getting a UV coating? Computers don't emit significant
UV any more, right?
2) The optician recommended an anti-glare coating too. I can see the value
of that for driving, but how about at the computer? What's your experience
and insight? (When I look at my computer through my uncoated glass lens
reading glasses, I don't notice any glare. At $40 for the coating, this
question is of significant financial interest.)

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