The fluorescent lamp is a major advancement and a commercial success in small-scale lighting since the original tungsten incandescent bulb. These bulbs are more efficient compared to incandescent bulbs. Fluorescence is the phenomenon in which absorption of light of a given wavelength by a fluorescent molecule is followed by the emission of light at longer wavelengths.
Types of Lighting, Fluorescent
A fluorescent bulb consists of a glass tube with an electrode at each end. Inside the tube is a small amount of inert gas (usually argon or an argon‑krypton mixture) and a trace of mercury. The inner surface of the glass is coated with a special material called a phosphor.
When the bulb is turned on, electricity flows between the electrodes and creates an electric arc. This arc excites the mercury atoms, pushing them to a higher energy state. As the atoms return to their normal (ground) state, they release that excess energy as ultraviolet (UV) light. UV light is invisible to the human eye and can be harmful in high doses.
The phosphor coating solves both problems. It absorbs the invisible UV light and re‑emits it as visible light. This two‑step process—absorbing higher‑energy UV radiation and emitting lower‑energy visible light—is known as fluorescence. Bulbs that operate on this principle are called fluorescent bulbs. Without the phosphor coating, the tube would only emit invisible, potentially harmful UV light and would not function as a practical light source.
In short: A fluorescent bulb uses electricity to excite mercury vapor, which produces UV light. A phosphor coating then converts that UV light into the visible light we see.
How do Fluorescent Lights work? (2:02)
Transcript: How do Fluorescent Lights work? (2:02)
Fluorescent lights are ubiquitous, they're used to light up signs, in restaurants, offices, homes, they are almost everywhere. In this video we'll explain how they work.
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, who was 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.
There are 4 main components to a fluorescent light. The first is an electrode. There is also a very small amount of mercury vapour and an inert nobel gas swirling around inside the tube. And lastly there is a phosphor coating on the outside. An important piece of the fluorescent puzzle to note is that the inside of the tube is kept well below atmospheric pressure, usually around 0.3% of atmospheric pressure. This ensures that the mercury remains as a vapor. Electricity first enters the light fixture, like a troffer, and through a ballast. The ballast – which regulates voltage, current, etc. and is necessary for a fluorescent bulb to light. The ballast feeds the electricity into the pins of the fluorescent bulb on both ends. Then, after the electricity enters through the pins, it flows to the electrodes inside the sealed glass tube, which is kept under low pressure. Electrons begin traveling across the tube, from one cathode to the other. Inside of the glass tube are inert gasses and mercury which are excited by the electrical current. The mercury vaporizes as electricity flows, this leads to the excitation of electrons and the subsequent electron relaxation to produce an invisible UV light that we actually cannot see with our naked eye. This uv light is then absorbed by the phosphor coating which leads to excitation of more electrons where upon relaxing they finally emit visible light and this is what we see.
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Fluorescent lamps are about 2 to 4 times as efficient as incandescent lamps at producing light at the wavelengths that are useful to humans. Thus, they run cooler for the same effective light output. The bulbs themselves also last a lot longer—10,000 to 20,000 hours versus 1,000 hours for a typical incandescent.
Fluorescent Tube Lighting
You have likely seen fluorescent tube lighting in hospitals, schools, or office buildings. Fluorescent lights require ballasts—devices that regulate the electrical current flowing through the tube. Ballasts are essential for starting the lamp and providing circuit protection.
Ballasts consume energy themselves, and certain types operate most efficiently when the lights remain on for extended periods rather than being frequently switched on and off. There are two main types of ballasts: electronic and magnetic. Older magnetic ballasts often cause noticeable flickering, while modern electronic ballasts provide steadier light.
The image below shows the different types of fluorescent tubes available on the market. In general, smaller-diameter tubes are more energy-efficient. However, fluorescent tubes are not simple replacements for standard incandescent light bulbs. They come in various lengths and have different pin configurations, so it's important to match the size and style of your existing fixture when doing a lighting upgrade. Additionally, installing more energy-efficient tubes may require upgrading the ballast as well.
Text description of the Fluorescent tube lighting image.
The image displays five fluorescent light tubes of varying diameters, arranged horizontally against a plain gray background. Each tube is labeled with text to the left: T2, T4, T5, T8, and T12. The tubes are organized from top to bottom, starting with the thinnest, labeled T2, and progressing to the thickest, labeled T12. The tubes are all white with metallic gray caps at each end where the electrical pins are located.
Full-size fluorescent lamps are available in several shapes, including straight, U-shaped, and circular configurations. Lamp diameters range from 1" to 2.5". The most common lamp type is the four-foot (F40), 1.5" diameter (also called T12) straight fluorescent lamp. More efficient fluorescent lamps are now available in smaller diameters, including the 1.25 " (also called T10) and 1" (also called T8).
Fluorescent lamps are available in color temperatures ranging from warm (2700 K) "incandescent-like" colors to very cool (6500 K) "daylight" colors.
Cool white (4100 K) is the most common fluorescent lamp color. Neutral white (3500 K) is becoming popular for office and retail use.
Compact Fluorescent Lamps (CFL)
Compact Fluorescent Lamps are miniaturized fluorescent lamps that usually have premium phosphors, which often come packaged with integral or modular ballast, as shown in the image below.
Text description of the Types of compact fluorescent bulbs available on the market image.
The image illustrates six types of compact fluorescent lamps against a light gray background. Each lamp is labeled with a letter from a to f. Lamp (a) has a single U-shaped tube. Lamp (b) features a double U-shaped design with two parallel tubes. Lamp (c) consists of three parallel U-shaped tubes. Lamp (d) has a bulbous, rounded shape on top. Lamp (e) is a modular circline and ballast. Lamp (f) is rmodular quad-tube and ballast. Each lamp has a screw-in base.
Compact Fluorescent Lamps have the following characteristics. They:
- Typically have a standard screw base that can be installed into nearly any table lamp or lighting fixture that accepts an incandescent lamp.
- Come in a variety of sizes and shapes and are being used as energy saving alternatives to incandescent lamps.
- Have a much longer life—6,000 to 20,000 hours (10 to 20 times longer), compared to 750 to 1000 hours for a standard incandescent.
- One of the major challenges of CLF is the disposal. Due to the use of mercury they cannot be put in household trash. Most home improvement stores have a disposal box on site or will need to be transported to local hazardous waste facility. Investigate where you can dispose of CLF bulbs in your community.
Text description of the Managing CFL Bulbs image.
The image is an informational poster titled "Why Recycle Bulbs?" It focuses on the dangers of CFL (Compact Fluorescent Lamp) bulbs and provides steps on how to recycle them. The top section of the poster shows the title with an illustration of a CFL bulb. Below, two main sections are presented side by side: "The Dangers of CFL Bulbs" on the left with a red color scheme, and "How to Recycle CFL Bulbs" on the right with a blue color scheme.
The left section lists three dangers: "Contains Mercury," "Pollution Hazard," and "Landfill Waste." Each danger is accompanied by an illustration—mercury is depicted as a bulb with a mercury droplet, pollution with a smoking factory, and landfill waste by a trash can overflowing with bulbs.
The right section outlines four steps for recycling: finding a recycling center, handling the bulbs with care, ensuring proper transport, and recycling responsibly. Each step features a corresponding icon such as a map, hand placing bulbs in a sealed bag, a car with bulbs in the trunk, and a recycling bin.
At the bottom is a green banner with "DO NOT THROW CFLs IN THE TRASH!" flanked by red circular icons highlighting "No Landfill," "No Incineration," and "No Hazardous Waste."
Text description of the Compact Fluorescent Bulbs image.
The image displays four different types of light bulbs lined up side by side on a white background. From left to right, the first bulb is a compact fluorescent lamp (CFL) with a spiral shape and a screw base. The second bulb is also a CFL with a tight, coiled spiral design and a screw base. The third bulb is a CFL with a more elongated spiral design; it features a screw base. The fourth and final bulb is an LED bulb with a smooth, dome-shaped top and a screw base.