mercury vapor lamp
The mercury vapor lamp is the oldest type of high-intensity discharge lighting, used primarily for street lighting.
Mercury vapor lamps provide about 50 lumens per watt. They cast a very cool blue/green white light. Most indoor mercury vapor lamps in arenas and gymnasiums have been replaced by metal halide lamps. Metal halide lamps have a higher color rendition index and a higher efficacy. However, like high-pressure sodium lamps, mercury vapor lamps have longer lifetimes (16,000–24,000 hours) than metal halide lamps.
Significant energy savings are also possible by replacing old mercury vapor lamps with newer high-pressure sodium lamps.