quickly fills an interior of the heat pipe 40 and whenever the vapor comes into contact with cooler walls of the heat pipe 40 i e the top surface of the heat pipe 40 which thermally contact with the heat sink 30 a it releases the heat to the heat sink 30 a after the heat is released the vapor condenses into liquid which is then brought back by the wick structure 42 to the evaporating region i e the connecting surface 43 of the heat pipe 40 since the heat pipe 40 transfers the heat by using phase change mechanism involving the working fluid the heat transferred to the heat pipe 40 from the led dies 14 is thus rapidly and evenly distributed over the entire heat pipe 40 and is then conveyed to the heat sink 30 a through which the heat is dissipated into ambient air obviously multiple heat pipes 40 can be used to increase the heat dissipation efficiency for the led assembly for example two or more heat pipes 40 can be thermally attached to the chassis 31 a of the heat sink 30 a also the chassis 31 a of the heat sink 30 a can define more grooves 311 for receiving the heat pipes 40 therein the.