Fluorescent lamp (tubular electric light)

Construction and how it works

Key parts are the glass tube, a low-pressure mercury–argon gas fill, a phosphor layer, electrodes at each end, and an electrical ballast. When the lamp is started, a discharge forms between the electrodes and excites mercury atoms. Those atoms emit ultraviolet photons, which strike the phosphor and are re-emitted as visible light. The ballast is essential: it limits current once the arc is established and, depending on design, provides starting voltage. Ballasts may be magnetic (older, heavier) or electronic (lighter, more efficient, quieter).

Types, sizes and starting methods

Linear tubes are commonly produced in several diameters identified by a "T" number that denotes tube diameter in eighths of an inch (for example T12, T8, T5). Lengths and wattages vary by market and application. Starting systems include preheat, rapid-start, and instant-start methods; each balances starting stress on electrodes, start time, and lamp life. Compact fluorescent lamps (CFLs) package these components into shapes intended to retrofit incandescent fixtures.

Performance, light quality and applications

Fluorescent lamps typically consume less electrical power and last longer than incandescent lamps producing similar lumen output, making them economical for many applications. They are widely used in commercial, institutional, and residential settings where diffuse, efficient lighting is required. Light quality depends on the phosphor formulation: lamps are made in different color temperatures and with different color-rendering properties. Some phosphors yield warm tones; others provide cooler, daylight-like light. Electronic ballasts and improved phosphors have reduced flicker and enhanced color rendering compared with early designs.

Environmental, safety and maintenance considerations

Because they contain a small amount of mercury, fluorescent lamps require careful handling, proper disposal, or recycling to avoid environmental contamination. Broken tubes can release mercury vapor and small contaminated particles; guidelines recommend ventilating the area, avoiding vacuuming, and using appropriate cleanup kits. Lamps can be sensitive to frequent on/off cycling and extreme cold, which affect lifespan and output. Comparisons of lifetime energy cost commonly show that a fluorescent lamp can save tens of dollars over the life of the lamp compared with incandescent alternatives; see more on energy and savings: energy information.

History and notable distinctions

Fluorescent lighting developed in the early 20th century as an efficient alternative to incandescent and early arc lights. Continuous improvements in phosphor chemistry, ballast electronics, and manufacturing have kept fluorescent technology widely used in large-area lighting even as LEDs have gained market share. Distinctive features that separate fluorescent lamps from other sources include the need for a ballast, the internal phosphor conversion process, and the presence of mercury. While modern fluorescent systems approach good color quality and high efficiency, considerations about disposal and dimming compatibility have driven many installations to evaluate LED replacements.

• Common advantages: energy efficiency, longer rated life, broad fixture compatibility.
• Common disadvantages: mercury content, ballast maintenance, potential flicker or hum with older ballasts.