In a fluorescent tube, electrical current jumps from an electrode at one end of the tube and flows through the tube and flows through the tube to an electrode at the other end. This current flow causes mercury and argon gases in the tube to emit ultraviolet (UV) light, which is not visible to the human eye. To make the ultraviolet light visible, the tube is coated with a phosphor powder that glows, or fluoresces, when it is struck by the light. When the fixture is turned off, the mercury/gas mixture within the tube does not conduct electricity. When power is first applied, several hundred volts are emitted form the ballast to initiate the release of electrical energy. Once this occurs, however, a much lower voltage is all that is required to maintain power-usually less than 100 volts for fluorescent tubes under 30 watts and 100 to 175 volts for tubes of 30 watts or more. When the higher voltage breaks down the gas and current begins to flow through it, the gas emits a great quantity of ultraviolet light but not much visible light. Only when the UV light hits the phosphor coating does the tube begin to glow. Different phosphors are used to achieve the light spectrum required for the fluorescent tube’s intended designation-cool white, warm white, colored, or black light.
Fluorescent bulbs are about two to four times more efficient at light production than incandescent bulbs. They also last a lot longer- 10,000 to 20,000 hours vs. 900-1000 hours for a typical incandescent. However, this does not take into account the expense of replacing fluorescent light ballast when one fails. Nevertheless, not all fluorescent bulbs require ballasts, and they are more energy-efficient than incandescent, providing two to four times more light per watt and using fewer watts than standard bulbs. They are also fairly maintenance-free.
One way to start a fluorescent light is to use a starter switch, sometimes known as a glow switch. The switch turns on when it is activated by an electric current. Inside it is a contact and a bimetal strip that provides the initial current surge that warms the bulb’s cathode (electron-emitting electrode). After the initial warm-up, the starter permits the electrical current to energize the gases in the tube. There are three types of starters: preheat rapid start, and instant start. In preheat starters; the electrodes are heated before high voltage is affected to the bulb. This type of starter is a replaceable twist-in module. Rapid start fixtures have electrodes that are constantly heated by low-voltage coiled wires (windings), and instant-start bulbs rely on step-up transformers for a short burst of high voltage to start up. The latter two types of starters are built into the ballast and cannot be independently replaced. The ballast is an enclosed component that governs the electric current-holding it to the level required to operate a fluorescent light properly. There are two types of ballasts: choke and therma-protected. Choke ballasts limit the amount of current flowing through the fluorescent tube. Fixtures that hold long fluorescent tubes use thermal-protected ballasts that include transformers as well as choke coils. With this type of ballast, when the light is turned on, a transformer momentarily steps up the voltage.
Another important aspect of florescent tubes is their pin configuration. The pins are the protrusions on each end that hold the tube in the fixture and transfer power to the tube. Fluorescent light fixtures commonly installed in homes use 4-foot-long bi-pin (two-pin) lamps. The two narrow pins on each end make these lamps difficult to install but easy to be loosened by normal vibrations. Once the base pins become loosened, the tube contacts disconnect, causing the light to flicker or go out.
A more reliable configuration is found on 8-foot-long tubes. These have a large pin on each end, and one is spring-loaded. They are equipped with an instant starter. They are easy to install and present few problems. Having one large connection on each end of the lamp eliminates the light flickering and corrosive tendencies of the smaller bi-pin tubes. In areas needing even more light, special fixtures with high-output tubes can be used.
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