Blargh, resistance is like...like...cheating!
Anyhow, haven't got OFP with me, but I think this is about the way to go about it:
figure out the loc of the streetlamp, and then place a game logic on it, name the gl something.
Then create a trigger, condition whatever (suggest you try it out first with just "true" though), and put something akin to this in the on activation field:
lamp=nearestObject[g1, "streetlamp"]; lamp switchLight "OFF"
(g1=name of gamelogic) can't remember the actual object name of the lamp, but I think that was it
If it doesn't work, complain. Haven't got OFP with me right now...
Wolfrug out.