How to check if sunglasses are really polarised

By Heymi Zhu, founder · Published 23 September 2026 · Last updated 23 September 2026

You need two things: an LCD screen and a second polarised lens. Hold the sunglasses in front of the screen, look through one lens and rotate the glasses a quarter turn. A polarised lens goes dark at one angle and clears at the other. Then cross the two lenses and rotate. Real polarised lenses block almost all the light at the crossing point. Tint alone does neither.

The LCD test

An LCD screen gives off light that is already polarised in one direction. That is why a polarised lens can cut it. Open a plain white page on a computer monitor or an older LCD phone screen, hold one lens in front of it, and turn the sunglasses slowly through 90 degrees.

• A polarised lens darkens as you rotate, then brightens again. The change is obvious.
• A tinted lens that is not polarised stays the same brightness through the whole turn.
• Some polarised lenses show a faint colour shift or a rainbow band at certain angles. This is normal and is another sign the polariser is present.

Use an LCD, not an OLED screen. Some newer phone screens do not emit strongly polarised light, which makes the test unreliable. A laptop or desktop monitor is a safer choice.

The two-lens test

Take two pairs of known polarised sunglasses, or the left and right lens of one pair, and hold one lens in front of the other. Turn the front lens. At roughly 90 degrees of rotation the two lenses together go almost black, because each polariser blocks the light the other lets through. Release the turn and the light returns. This test needs no screen and is a clean way to confirm a claim on the spot.

If the two lenses never block each other, at least one of them is not polarised.

What a polarised lens is for

Polarised lenses reduce glare from horizontal surfaces such as water, wet roads and car bonnets, because that reflected light is partly polarised. They are popular with people who drive, fish or ski. That is why the claim sells. It is also the easiest claim to fake, because a dark tint feels similar in a shop and the difference only shows up in glare conditions.

The label on the temple is not proof. A factory can print polarised on any frame. The two tests take a minute and settle it.

Put it in the contract

A claim on a catalogue is not an acceptance criterion. Write one into the order so a failure has a remedy. Useful clauses:

• Define the requirement by a test, not by a word. State that the lens must show polarisation under a standard test, and name the method.
• Keep a golden sample. A signed, dated pair the factory and you both hold is the reference for the batch.
• Test a sample from each batch, not just the pre-production sample.
• State the remedy. Ask for replacement or credit if a batch fails the test, and say who pays the return freight.
• Name the lens material and category alongside the polarisation claim, so the test report and the polariser are checked together.

Check the claim with the rest of the lens

Polarisation sits on top of other decisions. The lens material and the category decide the test report for your market, and a polarised film on the wrong lens still fails compliance. We cover the reports in our guide to sunglasses compliance, and the materials in TAC, polycarbonate and nylon lenses.

When we check a factory, we film the polarisation test on the floor and keep the footage with the lens documents in the report. See what that covers on the eyewear sourcing page or the main method page.

Written by Platinum Sky Sourcing, a service of Platinum Sky Group Limited (Hong Kong). We verify factories in China for overseas brands. Last updated 23 September 2026.