about : full for is mercury vapour lamp. A mercury-vapor lamp is a gas discharge lamp that uses an electric arc through vaporized mercury to produce light . The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger borosilicate glass bulb. The outer bulb may be clear or coated with a phosphor; in either case, the outer bulb provides thermal insulation , protection from the ultraviolet radiation the light produces, and a convenient mounting for the fused quartz arc tube. Mercury vapor lamps are more energy efficient than incandescent and most fluorescent lights , with luminous efficacies of 35 to 65 lumens/watt. [1] Their other advantages are a long bulb lifetime in the range of 24,000 hours and a high intensity, clear white light output. [1] For these reasons, they are used for large area overhead lighting, such as in factories, warehouses, and sports arenas as well as for streetlights. Clear mercury lamps produce white ligh