How Do Fluorescent Lights Fixtures Work?

How Fluorescent Lightbulbs Are Structured

To understand fluorescent light fixtures, you first have to understand fluorescent bulbs. A fluorescent bulb is a tube filled with argon gas and a bit of mercury vapor. There is an electrode on each side of the tube and a phosphor coating around the inside surface.

How Fluorescent Bulbs Work

When the light is turned on, electrons flow through the gas from one electrode to the other. When these electrons bump into the mercury molecules, they excite the mercury, moving some of its electrons to a higher energy level. The mercury electrons then discharge this energy, shooting out ultraviolet photons--small particles of light. These photons strike the phosphor surface, which absorbs their energy. A bit of this energy is wasted and turned into heat, but the rest is shot out again, this time as visible photons of light.

How the Lamp Starts the Bulb

The gas in fluorescent bulbs does not have many free electrons floating around, so electricity can not flow through it easily to begin with. To start the electric current flowing, the lamp has to cause a release of electrons into the bulb. There are a few different ways this is usually accomplished. Some lamps have a circuit that heats up the filaments, causing them to spew out electrons into the bulb. Others apply a brief, very high voltage to the electrodes, which overcomes the resistance of the gas and gets the current flowing.

How the Lamp Regulates Voltage

When you apply a voltage to a wire, it produces a continuous current that changes very little over time. With gas, however, the current tends to increase. Without anything to stop it, the current could increase so much in a fluorescent bulb that it would cause the bulb to burn out or even explode. The lamp regulates the current with a ballast. Fluorescent lamps use alternating current which switches direction many times a second, flowing back and forth between the two electrodes. The ballast is a coil of wire which restricts the flow of electricity. Every time the current switches, the coil creates a magnetic field which resists the change in the direction of the current. This slows down the build up of current temporarily, until the electricity can switch directions again.