Fluorescent lamp

Fluorescent lamp
Name	Fluorescent lamp
Caption	Various fluorescent lamps, including compact and linear types.
Classification	Gas-discharge lamp
Inventor	Edmund Germer, Friedrich Meyer, Hans Spanner
Inception	1926
Manufacturer	General Electric, Philips, Osram, Sylvania

Fluorescent lamp. A fluorescent lamp is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet light that then causes a phosphor coating on the inside of the lamp to glow. Developed commercially in the 1930s, these lamps became a dominant source of general illumination for offices, schools, and industrial spaces due to their significantly higher efficacy and longer life compared to incandescent lamps.

History and development

Early investigations into gas discharges and fluorescence were conducted by scientists like Michael Faraday and Heinrich Geissler. The foundational principle of converting ultraviolet light into visible light via phosphors was demonstrated by Nikola Tesla and Peter Cooper Hewitt in the early 20th century. The modern fluorescent lamp was patented in 1926 by the German team of Edmund Germer, Friedrich Meyer, and Hans Spanner of the company Deutsche Gasglühlicht. The patent was subsequently acquired by the American corporation General Electric, whose engineers, including George E. Inman, led development for mass production. The first public demonstration of the new lighting system occurred at the 1939 New York World's Fair and the Golden Gate International Exposition, catalyzing widespread commercial adoption in the post-war era.

Construction and operation

The lamp consists of a glass tube filled with an inert gas, typically argon, at low pressure, along with a small quantity of liquid mercury. Electrodes, usually made of coiled tungsten and coated with an emissive material like barium oxide, are sealed at each end. The interior surface of the tube is coated with a blend of phosphor powders, such as halophosphate or later rare-earth activated compounds. Operation requires a ballast to provide the necessary starting voltage and to limit the current during operation. When energized, the ballast causes a cathode discharge that vaporizes the mercury; the resulting electric arc produces ultraviolet radiation, predominantly at 254 nm, which is absorbed by the phosphor coating and re-emitted as visible light across a broad spectrum.

Types and configurations

The most common linear configuration is the T12, T8, and T5 lamp, where the "T" denotes tubular shape and the number indicates the diameter in eighths of an inch. The compact fluorescent lamp (CFL), integrating a tube and electronic ballast into a single unit, was pioneered by Edward E. Hammer at General Electric in the 1970s and later commercialized by manufacturers like Philips and Osram. Other variants include circline lamps, high-output and very-high-output lamps for industrial settings, and cold cathode fluorescent lamps used in backlighting for LCD screens. Specialized lamps with different phosphor blends are produced for applications such as germicidal irradiation, horticulture, and aquarium lighting.

Applications and usage

These lamps became ubiquitous in commercial and institutional buildings, providing illumination for offices, schools, retail stores, and hospitals. Their high efficacy made them standard for general ambient lighting in large spaces like factories, warehouses, and subway stations. The introduction of the CFL in the 1980s and 1990s expanded their use into residential settings as a direct replacement for incandescent bulbs. They are also employed in specialized roles, including backlighting for early flat-panel displays, photographic lighting, and in signage.

Comparison with other light sources

Compared to traditional incandescent lamps, fluorescent lamps produce significantly less heat and can be three to five times more efficacious, converting more electrical energy into visible light. However, they are generally less efficacious and have poorer color rendering than modern LED lamps, which have supplanted them in many applications. Unlike high-intensity discharge lamps such as metal-halide or sodium-vapor lamps, fluorescent lamps operate at lower brightness and are unsuitable for high-bay or outdoor area lighting over large distances. Their light output and starting performance can be adversely affected by low ambient temperatures.

Environmental impact and disposal

The primary environmental concern is the mercury content, a toxic heavy metal, which necessitates careful handling and recycling to prevent release into ecosystems. Many jurisdictions, including the European Union under the Waste Electrical and Electronic Equipment Directive and various U.S. states, have implemented strict regulations mandating lamp recycling. The energy efficiency of fluorescent lamps has contributed to significant reductions in carbon dioxide emissions from power plants like those operated by Duke Energy or Électricité de France compared to less efficient lighting. However, the shift toward even more efficient and mercury-free LED technology, driven by legislation such as the Energy Independence and Security Act of 2007, is leading to a decline in fluorescent lamp use and associated waste streams.

Category:Light sources Category:Gas discharge lamps Category:German inventions