Light Bulbs: Fluorescent Lamp



fluorescent lamps

 

Fluorescent Lamp

Primelite continues our look at the different types of light bulbs. From Incandescent to LED, lighting has changed immensely over the past 200+ years. In the past weeks we’ve taken a look at Incandescent Bulbs, Reflector Lamps (Incandescent) and Tungsten-Halogen Lamps. This week we’ll explore Fluorescent Lamps.

What is a Fluorescent Lamp.

fluorescent-cutaway01fA fluorescent lamp, also know as a fluorescent tube, is a low pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light.

Mercury-vapor gas discharge lamps are an artificial light source that generates light by sending an electrical discharge through an ionized gas. An electric current in the gas excites the mercury vapor which then produces short-wave ultraviolet light that then causes a phosphor coating on the inside of the bulb to glow. The fluorescent lamp converts electrical energy into useful light several times the efficacy of an incandescent bulb with comparable light output.

A preheat fluorescent lamp circuit using an automatic starting switch. A: Fluorescent tube, B: Power (+220 volts), C: Starter, D: Switch (bi-metallic thermostat), E: Capacitor, F: Filaments, G: Ballast

A fluorescent lamp tube is filled with a gas containing low pressure mercury vapor and argon, xenon, neon, or krypton. Light-emitting phosphors are applied as a paint-like coating to the inside of the tube. The lamp’s electrodes are typically made of coiled tungsten and usually referred to as cathodes because of their prime function of emitting electrons. For this, they are coated with a mixture of barium, strontium and calcium oxides chosen to have a low thermionic emission temperature. Fluorescent lamps use an auxiliary device, a ballast, to regulate the current flow through the lamp.

cooperlite

Fluorescent lamps were first developed in the mid to late 1800’s during the experiments leading to the development of the incandescent lamp. In 1856 a German glassblower named Heinrich Geissier created a “mercury vacuum pump” that evacuated a glass tube to an extant not previously achieved. The “Geissler tube” would produce a strong green glow when an electrical current was passed through. In 1859 Alexandre Edmond Becquerel experimented with the addition of luminescent materials coating the inside of the tubes. While the tubes were very inefficient and had a short life they did produce Fluorescence, the emission of visible light produced by a substance that has absorbed light or radiation in order to produce the visible light.

Further experiments using better forms of vacuum eventually leading to a gas-based lamp developed by Daniel McFarlan Moore, an employee of Thomas Edison. These lamps achieved some commercial success eventually leading Edison to purchase the patents in 1912. During this period Edison’s company developed the tungsten filament which lead to the extended lifespan of incandescent lamps. It would take General Electric another 2 decades to return to fluorescent development.

cooperLamp1bOne of the first mercury vapor lamps invented by Peter Cooper Hewitt, 1903. It was similar to a fluorescent lamp without the fluorescent coating on the tube, and produced greenish light. The round device under the lamp is the ballast.

Peter Cooper Hewitt developed and patented a lamp that glowed when electric current was passed through mercury-vapor. Hewitt’s lamps were also produced in standard sizes and operated at low voltages. It had limited uses due to its blue-green color output. In experiments fluorescent coatings were used for color correction. These mercury vapor lamps also foreshadowed the fluorescent lamp with their use of a ballast to maintain constant current.

In the early 1900’s experimentation would lead to the development of the neon lights and what would be the last step in the fluorescent lamp’s development – the fluorescent coating applied to the inside of the tube. In 1926 Jacques Risier received a patent for fluorescent coating for neon light tubes. In 1910 Georges Claude patent improved upon the electrode, reducing sputtering, and showing that gas based lighting was commercially feasible. By the end of the 1920’s all the major components of fluorescent lighting were in place: economically manufactured glass tubing, inert gasses for filling the tubes, electric ballasts, long lasting electrodes, the use of mercury vapor as an luminescence, the producing of a reliable electric discharge and a fluorescent coating that could be energized by ultraviolet light.

During the late 1920’s and early 1930’s General Electric controlled most of the development and marketing of fluorescent lamps due to its ownership of their related patents. It wasn’t until World War II that GE brought the “fluorescent lumiline lamps” to market. Available at first in 4 different tube sizes, the demand for the new lighting would grow rapidly due to the needs of wartime manufacturing. By 1951 more light would be produced, in the US, by fluorescent lamps than by incandescent lamps.

Today the compact fluorescent lamp (CFL), which we’ll look at next, has become important  as a replacement for the incandescent bulb as they are being phased out.  The CFL bulbs are more efferent, do not have temperature issues and are cheaper to light.

Series: Primelite looks at the light bulb:

Sources:

Wikipedia – Fluorescent Lamps
Fluorescent Lamp Phosphors
Photo: Peter Cooper Hewitt lamp – wikipedia
Photo: Fluorescent lamp circuit diagram – wikipedia