One thing I forgot - I finally got to see an upgrade of a traffic light from lights to LED yesterday. The process was rather simple - they took off the entire light housing from the top of the pole and put the new one on. Given that they only did the lower ones, and not the lights above the centre of the road, I am guessing that 240V is still fed to the lights, and that there is a power supply in the light. That is my guess anyway.