High lumen output quartz metal halide lamps are provided which comprise a vacuum outer fill, and a silicon nitride CVD coating on the outside of the quartz arc tubes (discharge tubes). Instead of nitrogen filled outers, vacuum lamp outers are used to reduce energy loss (since heat conduction loss is reduced) and to increase lumen output. Additionally, only the outside of the arc tubes is coated with silicon nitride, without coating the metal components. This reduces or blocks sodium diffusion through the quartz walls. The silicon nitride coating also retards migration of the trace hydrogen from the lamp outer into the arc tube. At least about a 10% increase, and preferably a 15% increase in lumen output is realized by using a vacuum lamp outer instead of the nitrogen fill outer conventionally used for the traditional quartz fill lamps. The heat conduction loss is reduced and the lamp efficiency is increased significantly.