Light pollution is trespass. The local zoning code may address the issue. Ours does, although few take advantage of it. There was a McDonalds that had to put up a noise fence and make custom shields for its lights and filter the stove smoke because they moved into a formerly residential area [zoned general use at the time], and faced all kinds of resistance and demonstrations from the residents. The restaurant would not have made these changes on its own, and was not about to move away. It would be more difficult to constrain a residential neighbor, but commercial interests have some urgency in keeping things moving.
I have to see if Idaho law treats it as such. Besides the idiot neighbor and his yard lights, the new building has windows on all 4 sides where the inside office lighting spills into 5 backyards. I would be satisified if the business killed the internal and external lighting at 9 PM each day. There isn't usually anything of astronomical interest before that time.