I just noticed an old column about streetlights going out as people walk by, and sadly, noticed that the topic was never really resolved.
I always believed this was mechanical, rather than electrical. For example, the lights on the drillfield at my alma mater, Virginia Tech, used to go out if you gave them a good whack, then come back on a few minutes later. We used to run around hitting them all so we could get the drillfield to utter darkness.
So, subsequently I always assumed this phenomenon (streetlights going out as you walked by) was something similar, caused by the vibration (or whatever) of your footfalls.