It appears that New Flyer uses HID lights on some of their transit buses. Do they just end up blinding oncoming drivers since I assume they do not have automatic leveling?
I dare say that buses - especially ones with air suspension - don't change their attitude much, no matter how heavily they are loaded. But it's still an interesting point - buses with HID lights here don't have either self-leveling or cleaning systems on the lights, so I guess the law requiring those features must exempt commercial vehicles.
Here's a light which is fitted, according the website of the bus parts supplier that I got the image from, as OEM equipment to Volvos, Auwarters, MANs, Neoplans and Liebherrs - it's clearly just a plain light, designed to be bolted into a square opening.