A fluorescent lamp is a low-pressure gas-discharge light source that converts electrical energy into visible illumination through fluorescence. It is a highly efficient alternative to traditional incandescent bulbs, commonly appearing in two primary forms. The most recognizable is the linear fluorescent tube, often found in commercial and industrial settings. Another common form is the compact fluorescent lamp (CFL), a smaller, often spiraled bulb designed to fit into standard household sockets.
Essential Internal Components
The lamp relies on several internal components sealed within a glass tube. At either end are coiled tungsten filaments, which serve as electrodes that initiate the electrical discharge. These electrodes are coated with an electron-emissive material to facilitate the release of electrons when heated. The tube contains a low-pressure mixture of inert gases, primarily Argon, and a trace amount of liquid mercury. The mercury vaporizes into a gas when the lamp is operating. The inner surface of the glass tube is coated with phosphor, a blend of chemical compounds that determines the color of the visible light produced.
The Three-Step Lighting Process
Light generation within the tube is a sequential three-step process beginning with the flow of electricity.
Step 1: Ionization and Arc Formation
The current heats the electrodes, releasing a stream of electrons into the tube’s interior. These free electrons collide with the inert gas atoms and the mercury vapor, causing the gas to become ionized and form a plasma. This process establishes an electrical arc that continuously flows between the electrodes.
Step 2: UV Light Generation
As electrons collide with the mercury atoms, they temporarily boost the atom’s outer electron to a higher energy level. The excited electron quickly drops back to its stable state, releasing the excess energy in the form of photons. The majority of these photons are high-energy, short-wave ultraviolet (UV) light, which is not visible to the human eye.
Step 3: Fluorescence
In the final step, this invisible UV light is converted into the visible light we observe. The UV photons strike the phosphor coating on the inner wall of the tube. The phosphor absorbs the high-energy UV radiation and then re-emits this energy at a longer, visible wavelength. This phenomenon is called fluorescence.
Managing the Electrical Current
A separate component called a ballast is required to manage the electrical current. When the gas inside the tube ionizes and converts into plasma, its electrical resistance drops significantly. Without a regulating device, the current drawn from the power source would rapidly increase, causing a “runaway current” that would quickly destroy the lamp. The ballast first provides a momentary high-voltage surge to start the arc and ionize the gas. Once the arc is established, the ballast acts as a current-limiting device, stabilizing the flow of electricity to the optimal level for continuous operation. This regulation ensures steady light output and a long service life.