Four

I had been hoping for something a little more spectacular to mark the completion of four gapless years of blipping, however, you've seen most of the subjects I've taken today before, and the nature of this seemed vaguely appropriate.

This is the light from the utility window on the wall opposite.  Looking at the window itself there is no obvious difference between the panes, but that's clearly not the case.  Bottom right will be original (or reproduction) antique glass, but the stripes on the upper two are a mystery.