A heat dissipating structure of a lightweight lamp cup 10 made of a porous material includes a containing cavity 11 at an end of the lamp cup 10, a lamp holder 30 at another end of the containing cavity 11, a metal hood 60 sheathed with the lamp holder 30 and covered onto an external side of the lamp cup 10, a heat conduction medium 50 between the lamp cup 10 and the metal hood 60, and a light emitting unit 20 contained in the containing cavity 11 of the lamp cup 10, such that the heat produced by the light emitting unit 20 can be conducted form the lamp cup 10 to the metal hood 60 and dissipated from the metal hood 60 to the outside.