Abstract: A plurality of disc-shaped substrates carry light emitters and are axially stacked, spaced apart, in a metal housing to dissipate the heat produced by the light emitters. The housing comprises mutually connected elongate planar ribs that abut the light emitters or substrates for thermally connecting the light emitters to the housing. The ribs have shoulders. The substrates are received between the ribs and abut the shoulders. The shoulders are positioned proximate each light emitter in intimate contact with the substrate for efficient heat dissipation.