水银灯亦称汞灯，是一种内部含有汞蒸气的灯，以气体放电的方式产生亮光。

灯管用耐热玻璃制成，两端装有电极；制造时抽去空气，充入水银和少量氩气；通电后水银蒸发，受电子激发而发光。

目前水银灯有「低压」、「高压」和「超高压」三种类型。高压水银灯发光效率高，使用寿命长，但紫外光多、红光少，可用作晒图机的光源；管壁涂荧光物质后产生白光，即高压水银荧光灯，可用作广场和街道的照明。低压水银灯发出强紫外光，可用作杀菌消毒；涂以荧光材料后，即日光灯。超高压水银灯是一种点光源，用于光学仪器。

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.