A light source includes a light head and a heat transfer arrangement. The light head includes a tubular supporting frame, which has an interior space, and a luminary unit provided on the supporting frame. The heat transfer arrangement, for dissipating heat generated from the light head, includes a heat sink and a heat conductor having a sealed chamber, which has a first portion in the supporting frame and a second portion extended to the heat sink, and a cooling agent contained in the sealed chamber of the heat conductor, wherein the cooling agent is capable of being vaporized by the heat of the luminary unit and condensed by said heat sink so as to substantially enable the heat to flow from the luminary unit towards the heat sink.