> Here in Germany they have metal shutters [...] Small correction: not metal, these are (mostly) made out of plastic nowadays, sometimes aluminum, and earlier

> Here in Germany they have metal shutters [...] Small correction: not metal, these are (mostly) made out of plastic nowadays, sometimes aluminum, and earlier, from wood. But yes, the effect if they aren't fully closed, is nicely adjustable to limit light without making a room pitch fark.