This is not a special effect

The living room in my flat faces just a little bit south of east. In summer it gets the sun early in the morning and in winter a bit later. There is a large horse chestnut tree outside the living room window. The light that enters the living room is dependent upon the time of year and how many leaves are on the chestnut tree. On the window there is an aluminium venetian blind. Sometimes light from the sun bounces off the surface of passing cars, it passes through the leaves of the chestnut tree, reflects off the aluminium venetian blinds and flashes on my walls and ceiling. It was a particularly sunny and windy day in winter when I noticed this light falling on my glass paperweight.