Fluorescent lamp
A fluorescent lamp is a type of electric lamp that excites argon and mercury vapor to create luminescence. Fluorescent lights are more efficient than conventional incandescent lamps because less of the energy is converted to heat. Instead, most is converted to usable light.
The fluorescent lamp was invented in 1900 by Edmund Germer.
A fluorescent light bulb is filled with a gas containing argon and mercury vapor, sometimes referred to as plasma when electrified. The inner surface of the bulb is coated with a fluorescent paint made of varying blends of metallic and rare-earth phosphor salts. The bulb's cathode bombards the vapor with electrons causing it to emit ultraviolet (UV) light at a wavelength of 254nm. The UV light is absorbed by the bulb's fluorescent coating, which re-radiates the energy at lower frequencies (longer wavelengths) to emit visible light. The blend of phosphors controls the color of the light, and along with the bulb's glass prevents the harmful UV light from escaping.
Fluorescent light bulbs come in many shapes and sizes. An increasingly popular one is the compact fluorescent (CF) light which screws into a regular light bulb socket. Their advantages over regular incandescent bulbs are their long life (6,000 to 10,000 hours instead of 750 to 1,000 hours) and energy savings due to their lower power; a 17-watt CF bulb gives the same amount of light as a 75-watt incandescent bulb, i.e. 1100 lumens. However, a large amount of the electrical energy is still converted into heat; the emitted visible light in this example is about 7 watts.
Unfortunately, many people find the color spectrum produced by some fluorescent lighting to be harsh and displeasing. It is common for a healthy person to appear with a sickly bluish skin tone under fluorescent lighting, and many pigments have a slightly different color when viewed under fluorescent light versus incandescent. This is mainly the case with fluorescent lamps containing the older halophosphate type phosphors (chemical formula Ca5(PO4)3(F,Cl):Sb3+,Mn2+), usually labeled as 'cool white'. The bad color reproduction is due to the fact that this phoshpor mainly emits yellow and blue light, and relatively little green and red. To the eye, this mixture looks white, but light reflected from surfaces has a distorted color. More expensive fluorescent lamps use a triphosphor mixture, based on europium and terbium ions, that have emission bands that are more evenly distributed over the spectrum of visible light and hence lead to more natural color reproduction.
Residential use of fluorescent lighting remains low (generally limited to kitchens, basements and other utility areas), but schools and businesses find the cost savings of fluorescents to be significant and only rarely use incandescent lights. In the U.S. and Canada, compact fluorescent lights have been steadlity increasing in sales for several years, as their quality increases, size and price decreases, color rendition improves, and more people find that the savings in energy costs (even indirectly, by saving on cooling) outweighs the initial cost.
Because they contain mercury, a toxic material, in quantities of a few milligrams per unit, fluorescent bulbs must be properly disposed of in many areas throughout the world. This generally applies only to large commercial buildings which produce many waste bulbs, though restrictions vary widely.
Bulbs are typically identified by a code such as F##T##, where F is for fluorescent, the first number indicates the power in watts (or strangely, length in inches in very long bulbs), the T is for tube, and the last number is diameter in eighths of an inch. Typical diameters are T12 (1½" or 38mm) for residential bulbs with old magnetic ballasts, T8 (1" or 25mm) for commercial energy-saving bulbs with electronic ballasts, and T5 (5/8" or 16mm) for very small bulbs which may even operate from a battery-powered device. High-output bulbs are brighter and draw more electrical current, have different ends on the pins so they cannot be used in the wrong fixture or with the wrong bulb, and are labeled F##T12HO, or F##T12VHO for very high output.
External links
- NASA: The Fluorescent Lamp: A plasma you can use
- How Stuff Works: Are fluorescent bulbs really more efficient than normal light bulbs?
- How Stuff Works: How Fluorescent Lamps Work