This is not a special effect

The living room in my flat faces just south of east, so in summer gets the sun early in the morning and in winter a bit later. There\\\'s a large horse chestnut tree outside the living room window. The light that enters my living room is dependent upon the time of year and how many leaves are on this tree. I also have a venetian blind. The street is busy with cars, sometimes when they pass, light from the sun reflects off their surface, through the chestnut tree and then the blinds. I see them pass as flashes of light on my walls and ceiling. This was a particularly sunny day in Winter...