After incandescents, fluorescent lamps are the second most common light
source. They are the most common source used in commercial buildings, producing
about two-thirds of our nation's illumination.
Fluorescents are easily distinguished by their tubular design. They come in circular, straight or bent in a "U" shapes.
In operation, an electric arc is drawn along the length of the tube. The
ultraviolet light produced by the arc activates a phosphor coating on the inside
wall of the tube, causing light to be produced. Unlike the incandescent lamp,
the fluorescent lamp requires a ballast to strike the electric arc in the tube
initially and to maintain the proper voltage and current to the lamp to maintain
that arc. Proper ballast selection is important to optimum light output and
lamp life.
Lamp sizes range from four watts to 215 watts. The efficiency (lumens per watt) of a lamp increases with lamp length (from four feet to eight feet). The reduced-wattage fluorescent lamps introduced in the last few years use from 10 percent to 20 percent less wattage than conventional fluorescent lamps, depending on size. For most applications, the cool white and warm white lamps provide very acceptable color and energy efficiency ratings.
Like the incandescent lamp, the fluorescent lamp can be dimmed, but not as easily. Dimming fluorescents is done with special ballasts and controls for dimming from 100% to 0% of output, or by multi-level ballasts that step down light output to specific levels (e.g., 75%, 50%, etc.).
Fluorescent lamp life is rated according to the number of operating hours per start, for example, 20,000 hours at three hours operation per start. The greater the number of hours operated per start, the greater the lamp life. Because fluorescent lamp life ratings have increased, however, the number of times you turn a lamp on or off has become less important. As a general rule, if a space is to be unoccupied for more than a few minutes, you should turn the lamps off.
Fluorescents are a good retrofit for incandescent lamps that operate a
significant number of hours. Circular fluorescent lamps can be used where exposed
socket incandescent bulbs are currently used. Compact or PL fluorescent lamps
(available in 5-40 watts) can be substituted for many incandescent bulbs and will
fit in many types of fixtures.
Facilities already using fluorescent lamps should consider high efficiency fluorescent lamp designs. They produce about the same amount of light, while saving about 10 to 15% of the energy usage.
Strengths:
4 to 5 times more efficient than incandescent, and an exceptionally long life
(10 to 20 times greater than incandescent).
Easy to maintain.
Lamp life is greatly affected by the average number of hours the lamp is
cycled on and off.
The lamps are also low cost and available in a wide range of sizes and colors.
Relatively low surface brightness and heat generation, and are relatively
insensitive to small changes in building voltage. This can be very important where
brownouts are common.
Weaknesses:
Most lamps are relatively large and require a relatively expensive fixture.
The ballasts in fluorescent fixtures can have an objectionable hum (some
louder than others).
Ballasts are now given a noise rating. Quiet ballasts are recommended for
office areas, louder and less expensive ballasts can be used in industrial
facilities.
Fluorescent lamps are temperature sensitive and may have difficulty starting
at low temperatures. Also, lumen output drops at low and high temperatures.
Special ballasts are available for low and high temperature applications.
While dimming of fluorescents is possible, it requires special, relatively
expensive ballasts.
For more detailed information . . .
