system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do 3D Movies look darker than 2D Movies?
gpt
3D movies work by projecting two different images, each polarized in a different direction.  The glasses that you wear have two polarized lenses that match the polarization of one of images.  So each lens blocks one of the images, while letting that eye see the other image, so that each eye sees a different image.  That produces the 3D effect.

But since each eye is only seeing half of the light being projected, the image looks darker.  3D movies use brighter projectors for this reason, but they're not twice as bright, so the light reaching each eye is still dimmer than a normal, 2D movie.