Why do control towers have tilted glass panels?
I'm pretty sure that has to do with reflections especially at night.

If you have ever stood between two mirriors you will understand the infinity mirror.



Light bounces back and forwards between the mirrors so when you look into them it appears like the scene goes on forever.

Window glass reflects a certain amount of light, like a mirror. In a control tower, where windows are all around you, if the surfaces of the windows are parallel you get that infinite mirror effect.

During daylight hours this can be seen as glare, but at night when you are trying to see that navigation light on Flight 594 amid a sea of runway and taxi-way lights, having your vision further confused by a myriad of reflections from the back window would be a bad thing. Further, since the room is a glass box, light can bounce all the way round the room. It would be quite possible to look off to your right and think so you see an unidentified aircraft approaching, but be actually seeing some truck's lights on the hill a couple of miles away over your right shoulder. 

Tilting the windows outwards means the reflection angle is towards the ceiling, which is generally painted black, and the effect goes away.

Further, tilting out means you can no longer see your own reflection, or reflections from other lit workstations in the window. Ever tried looking out of a window at night into the dark and only see your own ugly mug staring back at you, then tried to move your head to the side to see around yourself. LOL

Of course, for all this to work, the ceiling should be dark.

A few other reasons include, less affected by rain, fewer refraction effects, and external reflections. Bonus feature, less greenhouse effect and AC bills. Downside... darn hard to clean.