Measuring UV transmission?

[jeffsoptical]

I was watching I believe the Today Show on NBC talking about harmful effects of UV on the eyes. The Ophthalmologist was explaining the need for a good pair of sunglasses that blocks UVA, UVB. She said that not all sunglasses block UV, and you don't need a expensive pair of sunglasses to block UV. I have a BPI photometer and when I tint a pair of #3 gray sunglasses (CR-39) that I didn't UV, I still get almost 0% uv transmission.
Please explain to me why you need to uv cr-39 and then tint it #3 gray.

Jeff

[HarryChiling]

I was watching I believe the Today Show on NBC talking about harmful effects of UV on the eyes. The Ophthalmologist was explaining the need for a good pair of sunglasses that blocks UVA, UVB. She said that not all sunglasses block UV, and you don't need a expensive pair of sunglasses to block UV. I have a BPI photometer and when I tint a pair of #3 gray sunglasses (CR-39) that I didn't UV, I still get almost 0% uv transmission.
Please explain to me why you need to uv cr-39 and then tint it #3 gray.

Jeff

Jeff,

You don't need to UV a grey #3 lens, UV transmission is almost nil, the transmission of all other wavelegths is also low, that's why it's a sunglass. The today show changed up parts of that original story and they are idiots for bringing on someone who didn't knwo what they were talkign about.

[Barry Santini]

I was watching I believe the Today Show on NBC talking about harmful effects of UV on the eyes. The Ophthalmologist was explaining the need for a good pair of sunglasses that blocks UVA, UVB. She said that not all sunglasses block UV, and you don't need a expensive pair of sunglasses to block UV. I have a BPI photometer and when I tint a pair of #3 gray sunglasses (CR-39) that I didn't UV, I still get almost 0% uv transmission.
Please explain to me why you need to uv cr-39 and then tint it #3 gray.

Jeff

First of all, it would depend on what wavelength you use for the upper-end UV transmission:

380nm = ANSI & SOA standards
400nm = scientists and evolutionary biologists (they insist you would need to show them a hominid eye that "sees" light frequencies below 400nm)

You should simply use your BPI photometer on a clear CR39 before you tint it. Compare UV absorbtion before and afterward.

Barry

[Chris Ryser]

You should simply use your BPI photometer on a clear CR39 before you tint it. Compare UV absorbtion before and afterward.
Barry


Actually there is a little more to it..................above mentioned meter measures at 380nm...................point final.

If your absorption or transmission curve hops up or down below or above the 380nm mark is not shown as the instrument only measures at a given point.

CR39 will absorb fully up to 360nm due to added UV absorbers but will not cover UV A that goes to 400nm or even further (according to newest reports). Your ANSI figures are always tolerance figures telling you with how much off accuracy you can get away.

Only real spectrometer print out will give you the correct transmission curves. However any serious lens dye maker should have one and be able to supply or publish these transmission curves for every color they manufacture.

Here is a sample of transmission curves:
http://optochemicals.com/micro_highindex.htm

And if you want to read up on UV treatments I have another page: http://optochemicals.com/prism_article.htm

Actually a good UV absorber should show a straight and flat transmission line without bumps along the zero bottom line without so called windows..

A dye mix containing a lot of yellow will absorb a lot of UV, but will show Windows in some cases,

[Barry Santini]

Chris, as usual, you're right on about the BPI meters using 380nm.

I'm interested, however, in the inference you've made about UV *beyond* 400nm...can you elaborate?

Also, I use the "spectrometer" from Humphrey Zeiss. They say it meets all ANSI standards..what do you know about it?

Barry

[Chris Ryser]

I'm interested, however, in the inference you've made about UV *beyond* 400nm...can you elaborate?

Also, I use the "spectrometer" from Humphrey Zeiss. They say it meets all ANSI standards..what do you know about it?


Barry...............on question 1, I have to do some digging and find the right papers.

Your Humphrey spectrometer is a class higher than the regular UV meter and should be able to measure at 400 nm