Wow, great work from everyone!
The reflection theory is tempting, but I don’t see how an external light below the window could be reflected into the room at the necessary angle (by the usual incidence/reflection rule). Maybe if the window is double-glazed there could be some odd combination of reflection and refraction? If the window was partially open and tilted upwards a light below might be reflected inwards, but nothing in the larger photo supports that suggestion. Also ... Read even more
