An electrically driven L.E.D. lamp assembly (14) comprising an electrically insulating circuit board (26) having opposed first and second surfaces with light emitting diodes (28) having positive and negative leads (30, 32) mounted on the first surface. A plurality of pads (50) of thermally conductive plating are disposed on the second side with each pad (50) associated with the leads to conduct heat from each of the leads to one of the pads (50). A heat sink includes a base (36) overlying the second surface and layers (56, 58) of thermally conductive and electrically non-conductive material are disposed between the conductive plating and the heat sink (36) to secure the conductive plating and the circuit board (26) to the heat sink (36) while preventing a short between the conductive plating (50) and the heat sink (36). The assembly is characterized by a thermally insulating material (44) disposed over the heat sink (36) for sandwiching the heat sink against the conductive plating (50) to limit heat transfer into the heat sink from the outside.