Polarization Problem

[Visionheir]

I just started at LC, don't hate me I'm broke, and we had a customer come back with their prescription suns complaining about the polarization. Polarization Axis is correct, sph and cyl, axis too. They came in one time before for some bad stresses in the lens that made everything "wavy" which was true, we could see the stress fringes. Lenses were recut with less stress and now the customer is complaining of glare. She did a test where she held the glasses up to her computer screen and rotated them, and while the screen got very dim it didn't block all the light in any configuration. Does this mean that the polarization is defective since it allows through some polarized light be it from a screen, road glare, or other cause? We're going to ask a tech to inspect to some polarized blanks and see if these were abnormal, but if they are normal, do we just remake again and hope she doesn't notice or explain that the polarization isn't as effective as she expected it to be?

[Steve Machol]

<Post moved to its own thread>

[Boldt]

It may be that she is expecting to much from them. Ask her how she thinks they work and go from there. The computer screen test is an ok one I found, but with more modern screens it should not black them out. Use a polarized lens blank and see what happens.
Also no hate for the LC...well working there any way. Money is money.

[DanLiv]

Computer screens do not perfectly polarize light, so polarized lenses cannot block all the light at any angle. The best test of polarized lenses is to stack two lenses at 90 degrees to each other (cross polarization) and look through them. If they are good polarized lenses they will black out completely.

[Visionheir]

I may decline asking that question, since the customer was wearing her previous plano polarized sunglasses into the store so I don't want to seem patronizing. Is there a technical explanation for why the lenses wouldn't block all of the monitor? I've tested with my own 2 pairs of ray ban and carrera sunglasses and they block everything from my phone. I haven't tried my phone with her glasses though.

[Visionheir]

Thank you for the explanation.

[uncut]

I may decline asking that question, since the customer was wearing her previous plano polarized sunglasses into the store so I don't want to seem patronizing. Is there a technical explanation for why the lenses wouldn't block all of the monitor? I've tested with my own 2 pairs of ray ban and carrera sunglasses and they block everything from my phone. I haven't tried my phone with her glasses though.

I believe the answer lies in two main words, proximity, and parallelism. In physics, light bends or "leaks" around objects due to it's characteristics, so if the filters are not in very close proximity to each other, and are not parallell, light will be present.

[seeknowevil1]

If you are surfacing them make sure they are blocked up preciselely on the 180(horizontal) if not the polarization does not work precisely and that may cause problems

[sharpstick777]

I have seen defective polar blanks, I am suspecting it was a manufacturing error. But see them more in the summer when stocks get low.... me thinks manufacturers are binning their batches.

The second issue is compression because the lens is too big. Some stress is necessary, esp on very square or very round frames.

You can test both with another polarized lens. a full 90 degrees from your RX lenses and it should be totally black. If lights spots appear you have a defective blank.

Slightly off axis or under a circular polarizer stress will appear around the edges. If the stress crosses the field of vision resize the lens, usually by hand.

[HarryChiling]

Polarized lenses have an efficiency value as well (Polarized Coefficient), the patient should not expect 100% efficiency from their polarized lenses. I belive Younger toughts a 99.5% polarized efficiency and if the color is anything other than a dark grey expect that value to drop. Colors such as yellow blue and grey1 exhibit some polarization but nothing is going to give her 100% in an ophthalmic lens. 99%+ is a good polarized lens.

[Visionheir]

We're going ahead with a remake.

Tech is confident he is blocking correctly, doing the stress polarization test I saw clear spots next to the bridge, temple, and lowest point of the lens (aviator shape) and rotating them in different ways led to the clear spots turning different gradients/ Some gradients very lightly crossed the lower portion of the lens. What do you mean by "the field of vision" for a lens that covers most of the eye. Wouldn't all of the lens be in some way the field of vision?

Also, rotating rx against rx in any way never caused opaqueness. These are brown, I'd say a C but just called Brown. Using some of the blanks against blanks and blanks against rx there wasn't ever 100% blockage. Blanks didn't have significant stresses but that's probably obvious.

Thanks for the help, all.

We'll see how the pt likes the remake...

[Slim]

I check every one for bloom that comes in... if it's bad I hold them up to my lap top and use a marker and trace the bloom. Then hand edge the "clear areas" slightly to reduce the bloom to almost nothing as long as the lens still feels tight.