How Do Fluorescent Tubes Work?
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? Knowing how a lamp works can help you understand what might have happened when one stops working, making it easier to know how to fix it.
Below, we take a look at what's going on inside a fluorescent tube when you flick the light switch.
Where did it all begin?
According to the Smithsonian Institute in Washington, the fluorescent tube came about thanks to American electrical engineer and inventor Peter Cooper Hewitt's research into the work of physicist Julius Plucker and Heinrich Geissler, a glassblower. In 1901, when Hewitt passed an electric current through tiny amounts of mercury in one of Plucker's glass tubes, it lit up, making it the very first fluorescent tube to use mercury. These lamps work in much the same way today, with a few modifications of course.
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. These chemical components are:
- Inert gas
- Phosphor coating on the inside of the tube
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 noticed a powder-like substance, this is the phosphor powder which coats the inside of the glass.
Turning the light on
The basic process of lighting a fluorescent tube involves an electrical current provoking chemical reactions which result in a light being emitted. This is what happens when you turn on the light:
- The 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 of the tube.
- Manufacturers can offer different shades of lamps, such as warm white, cool white or even bright colours, by using a different blend of phosphors for each colour.
Fluorescent lights are more efficient than incandescent bulbs for two reasons:
- Incandescent bulbs create light through a heated filament and therefore create a lot of wasted energy through this heat, fluorescent tubes don't get hot as the current flowing through them creates UV light at a low pressure.
- Although both incandescent and fluorescent lights use ultraviolet the fluorescent tube puts the excess ultraviolet light to work, whereas an incandescent bulb produces ultraviolet light but does nothing with it.
We might summarise the process as follows:
- Switch light on
- An electrical current makes mercury into gas
- Gaseous mercury collides with electrons and atoms
- Electrons get excited and increase in energy
- Electrons relax after time and energy level comes down
- This causes a release of light photons
- The photons hit phosphor and become visible light