A high pressure gas discharge lamp 10 is described with a discharge vessel 20. Electrodes 24 project into a discharge space 22 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 comprises at least halides of Sodium and Scandium with a mass ratio of halides of Sodium and Scandium of 0.9-1.5. The lamp 10 further comprises an outer enclosure 18 provided around the discharge vessel 20, which is sealed and filled with a gas at a pressure below 1 bar. The lamp 10 has an efficiency equal to or greater than 90 lm/W in a steady state operation at an electrical power of 25 W.