Mercury lamp during start up

Front end of an old "cleartop" high-pressure mercury lamp during run-up, where the discharge tube in the center and the fluorescing coating on the outer bulb can be clearly seen. Although the magnesium fluorogermanate phosphor emits a deep-red colored light, the blue emission from the mercury discharge mixes up and gives an overall pinkish color. As the lamp temperature and pressure rise over time, the peak of visible emission in the mercury arc spectrum increases in intensity and shifts to the green region, giving to the lamp a white overall light with a greenish tint during full operation.

Credit : MaxFG