What kind of makeshift one have you been able to put together? I'm hoping for some good ideas, maybe yours is better than mine.
All I have as closest thing to a 'street light' is kinda expensive in terms of materials used and not what I picture as a street light - but I put up a large power pylon, and then stick a side mounting industrial wall light. The kind you would stick in a home, but it attaches to the side of a power pylon just fine, and as long as the pylon is wired, the proximity to the pylon auto powers the industrial wall light.
It causes a bit of a glow but it's not what I wanted as a real street light or street lamp per se. Hopefully Bethesda will add more actual objects and choices for settlement crafting, the variety is fairly slim pickings for almost all categories, and nil for street lighting.
I'd even settle for what you see in pre-scripted homes, like the string of lightbulbs on a wire that you see on roofs of some shacks and such. Too bad can't build those yet.