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About Fluorescent Technology
The major source for the information on this page is the writings of Dr. Louis A. Bloomfield, Professor of Physics, The University of Virginia. Specific source documents may be found at
http://howthingswork.virginia.edu/fluorescent_lamps.html
A fluorescent lamp consists of a gas-filled glass tube with an electrode at each end. This lamp emits light when a current of electrons passes through it from one electrode to the other and excites mercury atoms in the tube's vapor. The light that the mercury atoms emit is actually in the ultraviolet, where it can't be seen. To convert this ultraviolet light to visible light, the inside surface of the glass tube is coated with a fluorescent powder. When this fluorescent powder is exposed to ultraviolet light, it absorbs the light energy and re-emits some of it as visible light, a process called "fluorescence." The missing light energy is converted to thermal energy, making the tube slightly hot. By carefully selecting the fluorescent powders (called "phosphors"), the manufacturer of the light can tailor the light's coloration. Phosphors in CF bulbs are a mix to produce excellent color rendering and warmth similar to incandescent bulbs. Other phosphor mixtures are warm white, cool white, deluxe warm white, and deluxe cool white.
The only other significant component of the fluorescent lamp is its ballast. This device is needed to control the current flow through the tube. Gas discharges such as the one that occurs inside the lamp are notoriously unstable - - they're hard to start and, once they do start, tend to become too intense. To regulate the discharge, the ballast controls the amount of current flowing through the tube. In older lamps, this control is done by an electromagnetic device called an inductor. An inductor opposes current changes and keeps a relatively constant current flowing through the tube (although that current does stop and reverse directions each time the power line current reverses directions -- 120 times a second or 60 full cycles, over and back, in the United States). Most modern fluorescent lamps use electronic ballasts - - sophisticated electronic controls that regulate current with the help of transistor-like components.
Light Quality and Color
Color quality of light has two parts. The first is color temperature; this is whether the light appears 'warm' or 'cool'. Color temperature is expressed in degrees Kelvin (a scientific scale) with 2700K being similar to incandescent (yellow/warm) and 6000K being similar to sunlight (blue/cool). A candle's light is about 1500K. Most all CF bulbs today have a similar color to incandescent bulbs, or around 2700K. Note: You might have heard the term "full spectrum" in describing fluorescent lighting. This is nothing more than lighting with a color temperature of around 6000K. It is very blue, and can look quite unnatural in the home where we are accustomed to yellowish light. For more information about health claims regarding fluorescent light, visit
www.elflist.com/article02_spectrum.htm
or www.elflist.com/article01_sad.htm
.
The second part of light quality is color rendering. This is the ability of a light source to reveal the "true" relationship between colors. Color rendering is expressed numerically on the color rendering index (CRI), which is a scale from 0 to 100, with higher values being better. The sun is 100; any CRI of 80 or higher provides excellent color rendering. Most old style fluorescent tubes have poor color rendering ("cool-white" lamps have CRIs in the low 60's, while "warm-white" lamps are in the low 50's) which makes people and surfaces look bad (dull, distorted colors & greenish-gray complexions). Most T-8 fluorescent tubes and CF bulbs made today have CRI's in the 80's.
Related Links
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