The following animation is made from a sequence of frames of a single bolt of lightning captured on a digital camera in video mode during a lightning storm in NYC on Monday, 10th May 2004. It's an old image I was going to trash, but decided to post it here instead.

I thought it was strange how this particular bolt of lightning actually pulsed twice, but thanks to information from the NOAA, I now know why. What happens with a bolt of lightning is that initially a charge moves downward from the clouds in sections called step leaders, which produce a channel along which charge is deposited. Eventually it encounters something on the ground that is a good connection, and at that stage the 'circuit' is complete and the charge is lowered from cloud to ground. There is then a return stroke (or pulse) which is a flow of charge (or current) which produces a luminosity much brighter than the part that came down. This entire event usually takes less than half a second. The series of images below are the frame-by-frame sequence that makes up the animation, and clearly illustrates the much brighter second pulse.

The storm itself lasted a couple of hours at pretty high intensity. I had a few other shots, however the images captured from the video were very grainy and hard to clean up because the video resolution is very small compared to the still shots (and of course the fact that this was all recorded at night didn't help either), so this is all you get.