Why do busses have blacklights?

[Great Dave]

The AC Transit busses I see at night have purple lights inside, but only in the front half. Is this for those passengers who might be stoned or on mushrooms?

[funneefarmer]

My guess is so that the driver can see what's going on inside the bus without screwing up his ability to drive at night. Either that or they're using UV lights to kill all the nasty germs floating around in there.

[Great Dave]

Okay, but why not the whole bus? It would throw me off to have a brightly lit area anywhere in the car.