Why Do Screens Go Dark With Sunglasses? LCD screens work by controlling light that’s already polarized, meaning the light waves are aligned in one plane instead of spreading out randomly. Polarized sunglasses also contain a filter that blocks light unless it’s aligned with the same direction as the lens. When the LCD screen’s polarization and the sunglasses’ filter line up, the image looks normal. But if they’re rotated at different angles, the sunglasses block that light entirely. That’s why so