# While wearing polarized sunglasses, it is sometimes impossible to read the LCD display on calculators or electronic wristwatches. The display will be completely black. Why does this happen?

When you look at your display (showing $1$ for example) you see grey (light the was twisted and passes vertically polarized through Pol. 2) and the number, formed by "blocked" light.
If you wear polarized glasses it is possible that the axis of polarization of them is crossed with respect to the one transmitted by the lcd (around the number $1$). So you'll see black for number $1$ and black for the display, i.e., all black!