Fluorescent lights use electricity to excite mercury vapor. This produces ultraviolet light that causes a phosphor coating inside the bulb to glow.

Existing white LEDs are also based on blue ones, the light from which is used to excite a phosphor layer made of yttrium aluminium garnet (YAG).

Excited by the current, the mercury atoms emit ultraviolet light, which bombards the phosphor coating on the inside of the tube.