Fluorescent Lights: What Are They and How Do They Work?

We often take lighting for granted. We walk into a room, and our hand instinctively goes to the light switch. But have you ever thought about exactly what kind of light you’re turning on? (I do, because I’m a licensed electrician.)

Today we mostly hear about light-emitting diodes (LED). But the humble fluorescent lamp (aka lightbulb) is still around and as popular as ever, at least in certain situations.

If you’re not familiar with fluorescent lighting, the next time you’re in Target or Costco, look up. Unless they’ve updated all their lighting recently, you’re probably looking at fluorescent lamps. Those long, skinny tubes have been the go-to for large-space lighting for decades.

We talked to Terry McGowan, director of engineering at the American Lighting Association, and Joel Worthington, president of Mr. Electric, to learn more about the dependable, affordable fluorescent light.

What Are Fluorescent Lights?

Fluorescent lights are an energy-efficient lighting technology found in homes, commercial spaces, offices, schools and industry. They’re called “fluorescent” because of the way they produce light. If something “fluoresces,” it emits light in reaction to absorbing light or other electromagnetic radiation, usually of a different wavelength.

Before fluorescent technology, people relied on the incandescent lamp, which produces light by heating a tiny metal coil (called a filament) inside the glass. McGowan says the incandescent, nicknamed a “hot wire in a bottle,” put out about 10 lumens per watt. But it lost, and still loses, a ton of energy to heat.

The quest for efficiency drove the development of fluorescent technology, and it succeeded. The first fluorescent lamps upped that output to 60 to 70 lumens per watt.

McGowan says there was “some controversy about who did what and when.” But it’s generally believed General Electric (GE) brought the first commercial fluorescent lamps to market in the fall of 1938.

More than eighty years later and we’re still using this technology? Yep. Worthington says fluorescents are efficient, inexpensive and versatile. “No other type of lighting has historically cost less for general interior lighting,” he says.

Fluorescents are being phased out, but don’t panic. Worthington says fluorescents are “less common in new construction due to the growing popularity of LED lighting, but you can still purchase fluorescent lamps for existing fixtures.”

How Do Fluorescent Lights Work?

By passing an electric current through a gas or vapor.

Imagine a long fluorescent tube light, like you’d see in a grocery store. Inside the tube is an inert gas and a small amount of mercury. When you flip on the light, an electrical arc is generated from one end of the tube to the other, exciting the gas and mercury, which emits ultraviolet (UV) light.

To convert this invisible UV light into light we can see, manufacturers coat the inside of fluorescent lamps with a “phosphor,” a chemical that fluoresces when exposed to UV light. “The visible light that comes from fluorescent bulbs comes from the inside surface of the bulb itself,” McGowan says.

To control the flow of electricity, fluorescent lights require a “ballast,” a current-limiting device inside the light fixture — or in some cases, the lamp itself.

Fluorescent technology is different from incandescent, which produces light via heat, and the LED, which has “no gas, no tubing and no hot filament,” McGowan says. LEDs still use phosphor to produce visible light, but it’s painted right on the diode, a mixture of metals and alloys attached to the light housing.

“When the electricity flows, light is emitted directly from the surface of the LED,” McGowan says.

Evolution of Fluorescent Lights

Fluorescent lights come in tubes, circles and many other configurations, sizes and colors. But for decades, we lacked a great replacement for the small incandescent bulbs that screw into a light socket.

Enter the compact fluorescent lamp (CFL). This made fluorescent lamps “look more like an incandescent lamp in size,” McGowan says, “[though] it’s still a fluorescent lamp with a long arc tube and a ballast.”

Developed in the 1970s, CFLs have a glass tube, often in a spiral configuration, instead of a round glass globe. The ballast moved from the fixture to the base of the lightbulb itself, giving consumers the freedom to use fluorescents in regular light fixtures.

CFLs are more efficient than incandescents, and they have a much longer life: 6,000 to 15,000 hours compared to about 1,000 hours.

CFLs filled a need for increased efficiency and innovation, but never quite caught on despite concerted public campaigns, according to Energy Star. One drawback: Disposal.

Because fluorescent lamps contain mercury, Worthington says “handling and disposing of fluorescent bulbs requires some care.” That means taking them to a recycling center instead of throwing them in the garbage.

Fluorescent Lights: Pros and Cons

Clearly, fluorescent technology has made an impact. But are they right for you? Here are the pros and cons of fluorescent lighting.

Pros

• Good value: Fluorescents are inexpensive and come with low operational costs.
• Long life: Tubes can get 20,000 to 30,000 hours of use before replacement, while CFLs are rated for up to 15,000 hours.
• Widely available: Fluorescents are everywhere, for now.
• Good variety: Fluorescents are available in multiple colors, styles and light outputs.
• Easy: Because they’re lightweight, fluorescents are a snap to install and clean.

Cons

• Temperature sensitivity: Fluorescents don’t work well in the cold, and light output drops if they get too hot.
• Environmental concerns: Mercury from improper disposal can contaminate the soil and water.
• Complicated disposal: Fluorescent lamps must be brought to a recycling center or retail location, and not all accept them.
• Flicker: Fluorescent lights flicker more than incandescent.
• Poor dimming: Dimming fluorescent lighting is expensive and requires complicated circuitry.

Do Fluorescent Lights Have a Future?

Yes, but it’s likely a short one.

Fluorescent lightbulbs are “gradually being phased out in many regions due to their environmental impact and the advent of more energy-efficient alternatives,” Worthington says.

Mercury, the catalyst for the fluorescence, is a major neurotoxin. When fluorescent bulbs break or are disposed of improperly — which happens to an estimated 75% of all fluorescent bulbs in the U.S. — mercury can end up in lakes, rivers and wetlands, contaminating fish and shellfish.

Seven states currently ban the sale of general-use fluorescent lightbulbs: California, Vermont, Hawaii, Colorado, Oregon, Rhode Island and Maine. McGowan expects the Department of Energy (DOE) to tighten federal restrictions in the next couple of years as well.

At present, the DOE requires most lamps sold to put out at least 45 lumens per watt, which essentially bans incandescents. McGowan expects fluorescents to be next if DOE raises the standard to 100 lumens per watt as predicted.

Still, McGowan says fluorescent lights are everywhere, and it will take years to develop LED counterparts and replace all the existing lamps. Some applications, like incandescent oven lights, don’t yet have a good fluorescent replacement, let alone LED, so expect some technology overlap.

But as LEDs develop and costs drop, McGowan says “the virtual elimination of other types is likely.”

About the Experts

• Terry McGowan is director of technology for the American Lighting Association. He also worked for General Electric Lighting for more than 20 years.
• Joel Worthington is the president of Mr. Electric, a Neighborly company offering residential and commercial electrician services.
• Cathy Milbourn, press contact for the U.S. Environmental Protection Agency (EPA), provided background information on lighting innovations.