This was an experiment I made one night as I was walking in the dark. I kept the shutter open for 30 seconds, kept walking, and let what happened, happen. It came out kind of neat!
Came across this image from July 10 last year; it was initially just pure black. I increased the exposure digitally by a factor of 8, and you get all this fantastic colored noise; I wonder what I thought I was taking a picture of at the time, though.