Watch your backside!

[drk]

We now have some AR coatings that have back-side UV blocking. (I can't remember the names.)

I remember that the big brouhaha was a finding that regular ARCs tend to selectively reflect invisible UV right back to into your peepers.

So, what about this?

Say you have a photochromic lens...and you have ARC on the back that blocks UV from reflecting.

Is this good or bad?

If it's destructively interfered with or somehow absorbed, then less UV gets into the lens to darken it (from the back...the front's OK, still). So UV block on back side of photochromics BAD! (But maybe with regular AR, it's bouncing off, anyway, so..no big loss?)

OR

If the UV is transmitted through the lens, then there's extra UV to darken the lens. Back side UV block AR GOOD!


Which is it?

I'm so confused.

[lensmanmd]

Backside UV pass-through, very good! We apply it on all of our AR coatings, except sun lenses. The caveat here is that backside UV AR is actually a pass-through, not blocking. The idea is to pass the UV through and not have it reflect back into your eye. Please don't ask me why our sun backside is not a pass-through...we just haven't created the proper recipe yet, as our volume for this is fairly low.

[DanLiv]

Unless your talking about CR-39, all other materials block UV. Photochromic layer is on the front side of the lens, backside UV won't reach it even with pass-through AR (put a poly Transition lens backside down on your UV light). I don't know for sure whether pass-through or destructive interference for backside UV protection, but I wager DI since that's the whole technology of AR. If they could engineer pass through of UV, they could probably do so for visible wavelengths, and I would imagine pass through non-reflectance would be more effective than DI, more transmission. Since AR doesn't pass through, presumably AR doesn't have the tech to do so.

[drk]

You guys are smart!

Thank you!

[drk]

I do think this, though, DanLiv...

When destructive interference occurs, by Mr. Scott's "Cap'n, I canna change the laws of physics" dictum, the energy is passed through, after all. We can't obliterate energy. (Not yet, but as I get over 50, it makes me wonder where my energy has gone...)

But yeah, I totally forgot that the lens polymer is absorbing UV from the back side in most cases, these days. It's a moot point.

And as it applies to backside UV-destructive interference/UV-passthrough the polymer acts as a UV sink. (I just wanted to say "sink".)

[Hayde]

This is a thread I can sink my teeth into.

[Prentice Pro 9000]

Backside UV pass-through, very good! We apply it on all of our AR coatings, except sun lenses. The caveat here is that backside UV AR is actually a pass-through, not blocking. The idea is to pass the UV through and not have it reflect back into your eye. Please don't ask me why our sun backside is not a pass-through...we just haven't created the proper recipe yet, as our volume for this is fairly low.

Oh wow! I always thought that it was the same coating on both sides. Wouldn't it bounce back once it hits the front surface coating, or is absorbed by the lens?

[Slim]

test i did a while back... trans lens on the bottom with diff lens-coatings on top that are supposed to "block" uv but still turs the trans lens dark

set up




after

[Prentice Pro 9000]

Slim! Very industrious!