How can I test sunglasses at the thrift store for polarization?

June 12, 2021 8:47 AM

I buy my sunglasses at the thrift store and I would prefer polarized ones. I often try to look up the model # but not all sunglasses have the model # on them. I found guides online to look at shiny objects or a computer screen to determine polarization but it didn't help. I have some scrap pieces of polarized car window tint, could that help me? Is there a reliable way I can prepare to go in and determine which sunglasses are polarized? Thanks
posted by maxexam to Shopping (11 answers total)

Some cheap sunglasses you order from Amazon comes with a little cardboard with a print that only reflects a certain way thus you can see the polarization.

On the other hand, I think the easiest way is to look at your smartphone with them on. Then tilt your head 45 degrees to the right or left. If the screen goes dark, you have polarized lenses.

Here's some tips form Sunglasswarehouse https://www.sunglasswarehouse.com/blog/polarization-test/
posted by kschang at 8:52 AM on June 12, 2021 [8 favorites]

Hold up your scrap of window tint and the glasses. Rotate either one. If they’re both polarized, one orientation should be almost black, and 90 degrees offset should be significantly less dark. You can check your window tint in the same way, if it’s large enough to cut into two meaningful pieces.

[edit] Kschang is right too — since most LCDs have a polarizing filter in the stack up, that also works and is probably easier / doesn’t rely on the quality of your window tint scrap [/edit]
posted by Alterscape at 8:52 AM on June 12, 2021 [10 favorites]

Look at another pair of polarised sunglasses. The will do the dark/light thing as you turn them.
posted by How much is that froggie in the window at 9:01 AM on June 12, 2021 [20 favorites]

With the polarized sunglasses I have, if I rotate my phone screen, it'll turn black at one angle and visible at 90 degrees from that
posted by RustyBrooks at 9:23 AM on June 12, 2021 [2 favorites]

The phone screen thing will only work with some phones - I suspect it's LCD vs OLED, but my wife's Android goes black if I hold it sideways wearing my sunglasses, but my iPhone does not.

Otherwise, yes, as How much is that froggie in the window suggested, find a second pair of glasses you _know_ are polarised, and rotate the pair you want to check whilst looking through them. At some point, the lenses should go black.
posted by parm at 9:48 AM on June 12, 2021 [4 favorites]

Stand near a window and look at the back of your hand. Is there something arrestingly weird about what you see? Do you go, "Whoa, weird, my hand appears to be made out of some kind of velvet; it no longer reflects light the way skin does"? Then they're polarized.
posted by Don Pepino at 2:33 PM on June 12, 2021

My iphone works a little bit, enough where if when I rotate it (or the glasses) it pulses slightly, and then I know things are polarized.
posted by bbqturtle at 2:35 PM on June 12, 2021

Ok the only reliable way is another pair of polarized sunglasses. Wear the tester pai and hold the known good pai in front of on eye and rotate the lens. If the new pair are polarized you will see the alternating dark/transparent effect as they rotate.

Phones, cardboard, looking out a window are all iffy and sublte at best. The above is a 100% reliable method.
posted by chasles at 4:51 PM on June 12, 2021

It sounds like phones vary, but mine is not subtle, it goes from readable to solid black
posted by RustyBrooks at 5:36 PM on June 12, 2021

Pick up two pairs of the sunglasses you're considering, put one on and hold the other so you can look through it as you rotate it. If the view darkens, they're polarized. This works because, being the same brand & model, you'll know that both are polarized or both are not.
posted by TruncatedTiller at 5:45 AM on June 13, 2021 [2 favorites]

Use two of them.
posted by klangklangston at 6:31 PM on June 13, 2021