The amphitheater is open to the lawn in the back--at SPAC--and the ballet began at 8:00. So it wasn't pitch-black-dark in the very beginning, but it might have well as been. My attention was completely focused on the stage and the sketchbook was toned and the pencil was light. In effect, it was blind drawing.
So during intermission, it was fun to see what I'd done, and encouraging to see that some of the scribbles even made slight anatomical sense.
The next morning, I erased a couple of the scribbles that made the least sense, and used the new "clean" spaces to reinterpret a few blind scribbles. On some, I just drew over the blind scribbles, with little erasures where necessary.