How Do Fluorescent Light Bulbs Work?

We’re diving deep to teach you how different light sources produce light. This information can help you when you’re choosing lights for a new lighting project or maintaining the lights you already have. If you’ve ever tried researching this information, you know it can get overwhelming and complicated. So, I’m going to simplify it for you. In this post we’re covering fluorescent light bulbs…

Fluorescent light bulbs come in a range of shapes and sizes like linear, circline, and the ever-popular swirl of the compact fluorescent.

Though the various kinds of fluorescent light bulbs look very different, the way they function is fundamentally the same.

Fluorescent light bulbs contain the following:

• Mercury vapor
• Electrodes, wired to an electrical circuit
• A glass envelope with a white phosphor coating on the inside

Pretty simple, right? Now let’s look at how these elements work together to make light: 

1. When you turn on the lamp, electrical current flows through the electrodes. Electrons pass back and forth in the tube.

2. The electrons excite the mercury vapor in the tube, bumping the atoms’ electrons to higher levels. This causes the mercury to emit UV photons, or UV light, invisible to the human eye.

3. The phosphor coating converts UV light into visible light. This happens when a UV photon collides with a phosphor atom, bumping one of the phosphor electrons to a higher energy level, and heating up the atom. When the electron falls back to its normal level, it releases energy as a visible photon – the light you see.

One final note about fluorescent light bulbs:

All fluorescent light bulbs need a ballast to function. Sometimes this component is built into the light bulb itself, and other times it’s a separate piece you have to use in junction with the lamp.

A ballast is an electrical device used to supply the right voltage to start a fluorescent lamp, and limit it during operation. 

Fluorescent lights need ballasts because their gas components conduct electricity to operate. To turn on, the lamps need a certain current. As the lamp continues to operate, its electrical resistance decreases. Charged particles multiply, and the current can climb on its own gas discharge. If you keep the voltage constantly high, the lamp can burn out, so it helps to have a ballast regulate this.

What questions do you have about fluorescent lights? Please share them in the comments section!

(To learn how LEDs work, check out this blog post.)