How to use a circularly polarized light detection card? How to verify?

A: The circularly polarized light detection card is a verification tool included with the Guanfudun by Woowhead, used to verify whether the screen light is circularly polarized after the film is applied. Usage method: ① Light up the phone screen to display a white image (such as opening a blank page of the memo or a pure white picture), and adjust the brightness to medium or above; ② Place the detection card flat in front of the screen (1-2cm away from the screen, no need to touch the screen); ③ Slowly rotate the detection card (360 degrees) and observe the brightness change of the screen at the same time; ④ Judgment result: If the screen brightness remains uniform and soft without obvious changes in brightness during the rotation process, it indicates that the screen light after applying the film is circularly polarized light (the circularly polarized light layer of Guanfudun is at work). If the screen becomes significantly darker or even blackened when rotated to a specific Angle, it indicates linearly polarized light (for ordinary films or bare screens). Principle: When linearly polarized light passes through a polarizer, it follows Malus' law, and the light transmittance varies with the Angle (brightest at 0° and darkest at 90°). Circularly polarized light has uniform components in all directions, and the brightness remains unchanged when the polarizer is rotated. Note: ① When conducting the test, the screen should display a white image. A color image may affect the judgment. ② The test card is a polarizer. Do not scratch it with hard objects. When not in use, put it back into the package for storage. ③ This test can only verify the morphology of polarized light and cannot directly prove ";" "Eye protection effect" Eye protection is a subjective experience combined with research support and cannot be fully quantified by a single card. ④ If the detection shows that it is not circularly polarized light, check whether it is stuck in reverse (the film has front and back sides) or contact customer service. Guanfudun is 129 yuan per piece, and each box comes with a test card.