Re: "reduction in waste heat"
+1 to Nigel. I was in Minsk, Belarus last week and most of their traffic lights are thin flat panels with LEDs. They get very cold weather in winter and I'm guessing the lights would not accumulate much snow or need much heat to melt it off.
Here in the UK you see what look like LED array traffic lights but still in a big square box with shrouds - but we don;t get much properly cold weather or snow (practically none last year - and my son got a sledge for Xmas :-(