I remember when I was working some long hours about two years back in the studio, and when i was taking a rest on a sofa in a dark video editing room, I noticed light with quite sharp shadows hitting the ceiling, realizing it was street lamp outside. I immediately thought - hey, that would be a nice original detail to add to some evening interior viz someday. I then left archviz field more towards VFX, so i never got to actually employ the idea, but I am glad you did.
Few months ago, during summer, i observed very similar effect. It was sunny day, and there was sharp strong sun hitting the floor in my room but another sharp strong light hitting the ceiling as well, which turned out to be caustics from the reflection of car windshield outside. It looked as if I had two suns in my room, one shining from top, other one from the bottom.
And just a few days later, when I was sitting in the office, I had sun during sunset shining through the one side of the office, but i was on the side that was in the eastern part, yet from my side of the building, it looked like sunny day as well. There was a glass building across the street that reflected sunlight so perfectly my office was sunny pretty much all the day :)
These things make me realize how many more factors are there when it comes to light in real world. Of course simulating it using caustics would be painfully slow, but I guess we can try to fake it using addition lights placed in the scene, where no one would expect them to be, and getting very interesting results :)
