Fluorescent tubes are a common sight in public places, offices and schools but how much do you actually know about the inner workings of the fluorescent lamp. Do you know why they don’t heat up for example? We’ll take a brief look at what’s going on inside a fluorescent tube when you flick the light switch.
What’s inside the tube?
The inside of a fluorescent tube contains various chemical components and two electrodes at either end which are wired to an electrical circuit. The electrical circuit connects to an AC supply through contact pins at the end of the tube which connect to a light fitting. Inside the glass tube is a small amount of mercury and an inert gas like argon. If you’ve broken a fluorescent tube or come into contact with the inside of the tube you might have notice a powder like substance. This is a phosphor powder which coats the inside of the glass.
Turning the light on
The basically process of a fluorescent tube involves an electrical current provoking chemical reactions which end up with light being emitted. This is what happens when you turn on the light:
- Current flows through the electrical circuit to the electrodes
- Voltage from the electrodes causes electrons to migrate through the argon gas from one end of the tube to the other.
- The energy from this changes some of the liquid mercury into gas
- As electrons and charged atoms move through the tube they will collide with the mercury gas atoms.
- The collisions excite the atoms so electrons increase in energy levels.
- When the electrons calm down and return to their original energy level they release light photons
- These photons are ultraviolet but are made into visible light when they hit the phosphor coating.
We might summarise the process as follows:
Switch light on à electrical current à makes mercury into gas à gaseous mercury collides with electrons and atoms à electrons get excited and increase in energy à electrons relax after time and energy level comes down à causes a release of light photons à photons hit phosphor and become visible light
The reason a fluorescent light is seen as more efficient than an incandescent bulb is that the fluorescent tube puts the excess ultraviolet light to work, whereas an incandescent bulb produces ultraviolet light but does nothing with it.