Sunlight actually...it's their sun.
But yeah, the first time I managed to catch that in a station I was in, it was like, wow, that's cool. That video just makes it all that more dramatic because at the end the sunlight washes over where he's docked.
Fortunately I haven't had a station yet that was lined up perfectly with the sun shining straight in. There'd be lots of accidents leaving that one. Turn your lights on, everyone!