A heat sink, made of a highly heat-conductive material is placed on the back of a circuit board upon the front of which many LEDs are arrayed as the signal light source. The heat sink, generally formed as an aggregate of a number of fins, need not necessarily be fitted in one piece with the back face...http://www.google.se/patents/US4729076?utm_source=gb-gplus-sharePatent US4729076 - Signal light unit having heat dissipating function
