Powerful LEDs also run rather hot, more specifically their power circuits. My pocket size flashlight would easily run up to 100 degrees I think but it has protection built-in and steps down brightness when overheated. And it only has 1 LED and 1 lithium cell for power. So it probably would have been easy to design external radiators for traffic lights internals, with a heatpipe or similar solution. But they would be more expensive that way.
