Fluorescent lighting is a form of
electric discharge lighting.. A typical florescent lighting system consists of a
bulb,
bulb sockets and a
ballast. Fluorescent lighting is
energy efficient and the units themselves display long lives. They are often criticized for
noise and poor
color balance, but neither disadvantage is inherent to fluorescent lighting, but rather depends on the quality of the application.
Fluorescent Bulbs consist of a glass bulb with an electrode and base at each end. The inside of the bulb is coated with a phosphor. The air is removed and replaced with an inert gas and small amount of mercury.
The bulb operates because when sufficient voltage is applied to the bulb, electrons are released, flowing between the cathode and anode, setting up an electric discharge, or electrical arc between the mercury vapor in the tube. The mercury then radiates x-rays which strike the phosphor. The phosphor is excited, and emits visible light. The chemical composition of the phosphor determines what colors the light is emitted, almost any color balance, including that of natural sunlight may be selected.
Fluorescent lights have traditionally been regarded as requiring a lot of energy to start, but very efficient once in operation. This is because the lamp requires a rather high voltage to start. Early fluorescent lamps use a replaceable starter-- really a form of solenoid-- to keep the circuit closed until lamp temperature has risen far enough to maintain the circuit. The traditional delays seen when fluorescent lamps start comes from the need to heat the electrodes before the lamp will support the arc. Once in operation, the electrical resistance of the mercury drops, in fact, will never stop dropping until the lamp burns itself up. For this reason a ballast is necessary to stabilize the load at a minimum resistance, by adding reactance. Ballasts are wired in series with the amp to limit current flow. Traditional ballasts consist of a core and coil to generate reactance, a capacitor and a thermal protection device in a box, filled with potting compound to limit noise.
During the 1970’s the introduction of electronic ballasts revolutionized fluorescent lighting, providing improvements in noise, longevity and efficiency, particularly at startup. Traditional electromagnetic ballasts operate at the same frequency as the incoming AC power, which in the United States is 60 Hz. Electronic ballasts shift the operating frequency upward to between, 20 and 60 thousand Hz. Modern electronic ballasts may also use an instant start capability, by applying enough voltage on the line to begin the arc instantly. Rapid start ballasts keep the electrodes warm on a separate circuit inside the ballast. Electronic ballasts are also quiet compared to their electromagnetic predecessors.
There are several misconceptions about fluorescent lighting.
Fluorescent lights can be dimmed, by maintaining constant voltage while controlling the current passing through the lamp. A special type of ballast is required to dim the lights, and a special dimmer, but it can be done.
Fluorescent lights don’t have to make everything appear green. A greenish color balance is because you chose a bulb with an unnatural color balance. If you want more natural color, buy new bulbs. The designations are marked on the lamp, in fact the designations will tell you everything you need to know if you know the codes.
For example a bulb reading F40T1211CW designates a 40 watt bulb, Tubular in shape, 12/8 diameter in the Cool White color.
Fluorescent Color Codes
CW-Cool White
WW-Warm White (like an incandescent)
D- Daylight (natural sunlight)
CWX- Cool White Deluxe
WWX-Warm White Deluxe
B-Blue (literally blue)
P-Pink
G-Green
Ballast hum is the source of any noise. Ballasts are not necessarily noisy, and are rated according to their noise level. “A” designates the quietest ballasts, “F” the noisiest. Quiet costs, but an A ballast may even be used during recording, a B very pleasant for reading, an F best left to steel mills. Early ballasts were all very noisy, modern electronic ballasts are much better.
Because ballasts limit current through reactance, they can burn up, and are a potential fire hazard. P rated ballasts are thermally protected, and the installation of a small in line fuse can protect any fixture at little cost. The manufacturer will recommend a fuse, if asked.
Modern fluorescent lights are very good, with none of the drawbacks of the early systems. They do have a high initial cost, but this is offset by their much lesser life cycle costs. If you wish to install fixtures in a place where you plan to stay, the additional purchase expense will be well rewarded down the road.