Lux is a casual, minimalistic arcade game.
The premisse is simple. The world is covered in complete darkness, but there is one single light beam flying around through space. You "control" some mirrors that you can use to reflect the light beam in a loop. The main problem comes apparant quickly though... Those mirrors can move around but aren't really controllable forever.
Now it's up to you to not let the entire world be convered by complete darkness.