Fluorescent Lighting

Fluorescent lighting is a form of electric lighting based on the gas-discharge lamp. A fluorescent lamp produces light by passing an electric current through a low-pressure gas, rather than by heating a filament as an incandescent bulb does. Because much less of the energy is wasted as heat, fluorescent lamps are considerably more efficient than incandescent bulbs and were for many decades the dominant technology for lighting offices, schools and commercial buildings.

A typical fluorescent tube is a sealed glass cylinder containing a small amount of mercury vapour and an inert gas, with an electrode at each end. When current flows through the tube, it excites the mercury vapour, which emits mainly ultraviolet light. This ultraviolet radiation strikes a phosphor coating on the inside of the glass, and the phosphor fluoresces, converting the invisible ultraviolet into visible light. The choice of phosphor blend determines the colour appearance of the lamp, from cool white to warmer tones.

Because a gas discharge does not by itself limit the current it draws, fluorescent lamps require a device called a ballast to regulate the current and prevent the lamp from destroying itself. Older designs used a magnetic ballast together with a separate starter to initiate the discharge, while modern lamps commonly use electronic ballasts that operate at high frequency, reducing flicker and improving efficiency. Compact fluorescent lamps applied the same principle in a smaller, screw-in form, though light-emitting diode (LED) lighting has since become the more common efficient alternative.

Frequently asked questions

How does a fluorescent lamp produce light?

Current excites mercury vapour inside the tube, which emits ultraviolet light. A phosphor coating then converts that ultraviolet radiation into visible light.

Why does a fluorescent lamp need a ballast?

A gas discharge does not limit its own current, so a ballast is required to regulate the current and keep the lamp operating safely and stably.

Why are fluorescent lamps more efficient than incandescent bulbs?

They generate light through a gas discharge and phosphor conversion rather than heating a filament, so far less energy is lost as heat.