Referring to sun lenses only. Does anyone happen to know if Polycore and Hoya CR-39 lenses without AR/scratch resistance have UV400 protection? Sadly I can't find this information anywhere.
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Referring to sun lenses only. Does anyone happen to know if Polycore and Hoya CR-39 lenses without AR/scratch resistance have UV400 protection? Sadly I can't find this information anywhere.
Quote:
Originally Posted by Airegin
Any untreated CR39 lens material will give a full 100% transmittance.
I came up with the first successful commercially available product called *UV Protec* in 1982, where you treated the lenses in the hot solution for 25 minutes to treat the lens for a 100% protection by filling the lens pores with protective and UV absorbing crystals.
2 years later we came up with a version that would do the job in 5 to 10 minutes.
I'm sorry but that couldn't be further from the truth. I know for a fact that untreated untinted CR-39 has 100% UVB protection and at least some UVA (up to 90%). On top of that the lenses I'm asking about are tinted and block 85% of light, no way you get 100% UV transmittance here.
I figure it won't be easy to come up with a clear answer as both companies do not provide this information. CR-39 in general may not be the best choice for optimal protection. Can I at least be sure of 100% UVA protection if I order MR-8 lenses?
Not sure where you are getting your CR39 from, but most of our untreated CR39 lenses at dress thickness transmit in excess of 32% UVA, no where near 90% protection claimed here. Of course, Zeiss and Essilor have added UV inhibitors in their newest batch of CR39 pucks, but this is not yet an industry standard.
CR-39 does in fact block ALL UVC, UVB, and for most practical purposes, almost all UVA on it's own. Darryl had some excellent insight on this very topic more than 13 years ago. Search function is useful in discussions like this, as the tech hasn't changed...
https://www.optiboard.com/forums/showthread.php/13620-Why-does-CR-39-not-have-UV-protection?p=108257&viewfull=1#post108257
Depends on where you define UV ends. Old/ANSI standards used 380nm. Biologists say 400nm and below, since they cannot show any signifucant cone firings in the range from 380nm to 400nm.
Using 380nm, untreated CR39blocks 92% of UVA.
B
Barry
most of what I measure on CR39 is in the neighborhood of 68%. Where are you getting 92%
Here is an old school (2010)rundown of lens material properties that may be useful
Lens Material Properties Material Index Specific Gravity (g/cm3) Abbe Reflectannce Transmittance UVA (286 - 320 nm) Transmittance UVB (320 - 380 nm) CR-39 1.50 1.32 58 4.0 10.3 0.0 Poly 1.58 1.21 29 5.2 0.0 0.0 1.60 (MR6) 1.60 1.22 42 5.3 0.0 0.0 1.66 (MR7) 1.66 1.35 32 6.2 0.0 0.0 Trivex 1.53 1.11 46 4.4 0.0 0.0 Crown Glass 1.52 2.54 59 4.3 84.3 30.5 1.60 Glass 1.60 2.60 42 5.3 39.1 0.1 1.70 Glass 1.71 3.20 35 6.7 24.6 0.0 1.80 Glass 1.81 3.66 25 8.2 19.5 0.0
only a clarification
UV A 315-380 nm ( some literary sources say up to 400 nm)
UV B 280-315 nm
transmission data are +/- ok but culumn 5 and 6 are exchanged n°5 is UVA 315-380 and culumn 6 is UVB 280-315 nm