Fluorescent Lamps

Components of a Fluorescent Lamp:

• Tube . .?Usually straight glass tubing. May also be circular or U-shaped glass.
• Base . .?Several different types of bases are used to connect the tube to the electric circuit (fixture) and to support the tube in the holder (socket).
  • Bi-Pin
  • Single Pin
  • Recessed Double Contact (RDC)
• Phosphor . .?Powders with which the inside of the fluorescent tube is coated. This coating on the inside of the tube transforms the ultraviolet radiation into visible light. By combining different phosphors in varying proportions, it is possible to produce lamps in a wide variety of colors. Some of the newer fluorescent colors require the use of a tri-phosphor. Tri-phosphor is a combination of expensive rare earth phosphors.?Note: all fluorescent tubes appear white when not lighted, except Blacklite Blue, Gold, and Red.
• Gas . .?Usually argon or a mixture of inert gasses at low pressure. Krypton is sometimes used, especially in energy saver tubes.
• Lead Wires . .?These wires are connected to the base pins and carry the current to and from the cathode.
• Exhaust Tube . .?Air is exhausted out of the tube and the inert gas is added through this tube during the manufacturing process.
• Cathode . .?The cathode is coated with emissive material which emits electrons and is needed to generate an arc of electrons across the tube.

Workings of a Fluorescent Lamp:

• Electrons flow from one electrode (cathode) to the other. Collisions between these electrons and the mercury atoms cause an emission of radiation in the ultraviolet region which is not visible to the naked human eye. When this ultraviolet energy hits the phosphor coating it “fluoresces”, generating wavelengths of light that are visible to the naked human eye. The phosphor converts the invisible ultraviolet energy into visible light.

Fluorescent Lamp System:

• A fluorescent tube. A ballast (a device that controls or limits the flow of current in a circuit). Sockets (which support fluorescent tubes and provide electrical connections). A fixture (the device that holds the ballast, sockets, and tube).

Three Basic Fluorescent Types:

• Preheat . .?Introduced in 1939, the “original fluorescent lamp”. Cathodes must be preheated to electron emitting temperature before the lamp will light. Requires the use of a separate starter which supplies several seconds of current flow through the cathodes to preheat them between the time the tube is turned on and the time the lamp emits light.
• Instant Start . .?Introduced in 1944 to eliminate the slow starting of preheat lamps. Designed to withstand a higher starting voltage. Does not require any preheating of the cathode with the aid of a starter.
• Rapid Start . .?Introduced in 1952. Starts smoothly and quickly without the aid of a starter. The immediate heating of the cathode starts the tube in one to two seconds, and a lower starting voltage is required than with instant start.