Hey there, FFAK
Try:
(object
ID) switchlight "off"
where
ID is the number of your streetlight (get it by clicking the
show ID's button and zooming in until you see numbers).
The syntax for switchlight in the command reference uses the nearestobject command, which was necessary before Resistance as there were no object ID's. There's actually two commands in there, which is why it was a bit confusing