A high pressure gas discharge lamp includes a discharge vessel with electrodes that project into a discharge space of a volume of 12-20 mm3. The discharge space has a filling of rare gas and a metal halide composition which is free of mercury. The metal halide composition includes at least halides of Sodium and Scandium with a mass ratio of halides of Sodium and Scandium of 0.9-1.5. The lamp further includes an outer enclosure provided around the discharge vessel. The outer enclosure is sealed and filled with a gas at a pressure below 1 bar. The lamp has an efficiency equal to or greater than 90 Im/W in a steady state operation at an electrical power of 25 W.