I don't know. It's similar. I wonder what the problems are with using it, then?

One idea that comes to mind is that a regular screen leaks light. If you adjust the brightness on your laptop as low as it will go, then display a black image, there's still a massive difference between what you see there vs when the screen is completely powered off. But if you take two sheets of polarizing filter and stick them in front of your screen, you can get almost perfect blackness. That's why I thought it was a different idea, since the difference is so dramatic. You can block almost all the light, whereas a regular screen doesn't seem to be able to get that kind of contrast.