Abstract: A long life mercury vapor discharge lamp is provided. The lamp has a ultraviolet-reflective barrier layer, a rare earth triphosphor layer coated on the barrier layer, and a fill gas of mercury vapor and argon. Most preferably, the barrier layer has a coating weight about 2.6, mg/cm2, the phosphor layer has a coating weight of about comprising a light-transmissive glass envelope having an inner surface, means for providing a discharge, an ultraviolet reflecting barrier layer comprising alumina particles coated adjacent said inner surface of said glass envelope, a phosphor layer coated adjacent said barrier layer, and a discharge-sustaining fill gas of mercury vapor and argon sealed inside said envelope, said fill gas having a pressure of 2.9-5 torr at 25° C., said phosphor layer having a coating weight of 2-3.5 mg/cm2.