Or if you're not using that fancy RES malarky, you can do it with some good ol' fashioned nearestObject'ing.
place gamelogic close to where the lamppost is, name gamelogic (GL1, in example).
Make trigger, and place following into activation field:
lamp= nearestObject [GL1, "StreetLamp"]; lamp switchLight "OFF"
should do the same as mikeb's suggestion. Although if you do it his way you're a wuss. Godarnit. (*needs OFP:R*)
Just repeat for all streetlamps. Good luck!
Wolfrug out.