Maybe a little OT, but these were the lights I went with on my utility trailer. The outer ring is the tail/running light, and when you step on the brake, the inside lights up (and I believe the outside gets brighter as well.) I didn't like any of the standard kit lights where the whole thing just gets brighter when you hit the brakes - you can't always tell if its glare, or someone stepping on the brakes.
https://www.instagram.com/p/BW54qlWlORj/
I'd love to keep the same style when I get a bus.
(These particular lights came from Etrailer.com, but I don't know if they come in bus sizes. These are 3.5" I believe.)