destroy all 21 street lights (lamp posts) in Episode 1 Chapter 1. also do not destroy the Traffic Lights or it will cause the achievement to Not Trigger (thanks to Spilner for this info.)
these are the red/orange lights sitting on the grey poles with the blue/green base and top. the traffic lights to avoid destroying are not the realistic looking ones, but the lego ones that look very similar to the street lights. they have a red and a green lego stud on top. you do not have to complete the level, the achievement should unlock after destroying the last light.
1: (easy to miss) from level start, go left. there is one in the bottom corner by the gate.
2-5: along the first "city block" right on the street.
6: climb up and over the chemical spill, it's behind the damaged leaking truck.
AVOID: traffic light right after #6, on the street corner.
7-9: in the side street that goes back to a dead end with a dumpster and riddler box, just after the chemical spill.
10: below the second "realistic" traffic light, right where the street is all torn up.
11: right next to the cement truck that you must use explosives to get past.
12: right after #11 on the next street corner.
AVOID: traffic light right after #12, on the opposite corner of the block.
13: in the far right corner of the level, right after the long truck filled with silver objects.
14: after passing the truck and moving to the next section of the level, just before the two riddler boxes.
15: when the street starts to go downhill, stay above on the sidewalk, right after the same two riddler boxes.
16-21: they are all located together, surrounding the 4 tall green bushes / trees.