A fluorescent light fitting works by passing an electric current through a gas-filled tube, which excites the gas and produces ultraviolet (UV) light. This UV light then strikes a phosphor coating on the inside of the tube, causing it to fluoresce and emit visible light.
Here's a more detailed breakdown:
Key Components
- Glass Tube: Contains a mixture of noble gases (like argon or krypton) and a small amount of mercury vapor.
- Filament Emitters (Electrodes): Located at each end of the tube. These are heated to emit electrons.
- Phosphor Coating: Covers the inside of the glass tube. It's designed to glow when struck by UV light.
- Ballast: Regulates the current flowing through the tube. This is crucial because the resistance of the gas drops as it ionizes, which can lead to a runaway current and damage the bulb.
- Starter (Sometimes integrated into the ballast): Provides a brief voltage surge to help initiate the ionization process.
The Process Explained
- Starting the Lamp: When the light is switched on, the ballast sends a voltage surge to the filaments at each end of the tube. This heats the filaments, causing them to emit electrons. The starter (if separate) helps facilitate this process.
- Ionization: The emitted electrons collide with the gas atoms (noble gases and mercury vapor) inside the tube. These collisions knock electrons off the gas atoms, creating ions. This process is called impact ionization.
- Plasma Formation: As more ions and electrons are created, the gas becomes a plasma, a conductive state of matter. This allows current to flow between the electrodes.
- UV Light Generation: The moving electrons within the plasma collide with mercury atoms, exciting them. When these excited mercury atoms return to their normal state, they release energy in the form of ultraviolet (UV) light.
- Fluorescence: The UV light strikes the phosphor coating on the inside of the tube. The phosphor absorbs the UV light and re-emits it as visible light. The specific colors of light emitted depend on the type of phosphor used.
- Current Regulation: The ballast plays a critical role in regulating the current flowing through the tube. Without it, the current would increase rapidly, potentially damaging the light.
Simplified Analogy:
Imagine a pinball machine. The filaments are like the flippers, launching electrons (the pinball) into the gas (the play area). The electrons hit the mercury atoms (targets), causing them to emit UV light. This UV light then hits the phosphor coating (like a reflective surface), converting the UV light into visible light that we see.
Ballast Importance
The ballast is crucial for the fluorescent light’s operation. It performs two main functions:
- Provides high voltage initially: It delivers a high voltage to start the lamp.
- Limits the current: After the lamp has started, it limits the current to prevent the lamp from overheating and burning out.
Note on Intact Light Bulbs
The ionization process described above is contingent on the bulb being intact and containing the correct gas mixture. A broken bulb will not function.