Fluorescent lamp

types of fluorescent lamps

1. INFORMATION SHEET 5.1 FLUORESCENT LIGHTING FIXTURES

2. FLUORESCENT LAMP a form of electric discharge light source. It consists of a glass tube containing mercury vapor at a low pressure and inert gas like argon and krypton. The interior is coated with phosphor, which glows or fluoresces when exposed to ultraviolet light.

3. PEC Rules on Wire Dressing and Termination: Article 6.3.1.3 Live Parts. Fixtures, lamp holders, lamps, rosettes, and receptacles shall have no live parts normally exposed to contact. Exposed accessible terminals in lamp holders, receptacles, and switches shall not be installed in metal fixture canopies or in open bases of portable table or floor lamps. All joints/splices to be done must be properly insulated with spaghetti sleeving , wrapped with electrical tape having a similar thickness of the conductor used.

4. TYPES OF ELECTRIC DISCHARGE FLUORESCENT LAMPS

5. Pre-heat starting, hot-cathode requires starter (glow switch) and is pre-heated during starting. It uses a ballast to produce high voltage to start the lamp into operation and to limit the flow of current.

6. Operation of pre-heat type fluorescent lamp The tube filaments, starter (glow switch), and ballast are all connected in series, which constitute a complete circuit once the switch, is closed. As a current flow through, the gas (inert) inside the starter glows and the electrodes are heated. Since one of the electrodes is a bi-metal, it bends and makes contact with the other. At this instant, the circuit is metallically complete. The filaments of the fluorescent tube are then heated and partial ionization takes place. The bi-metals in the starter cools and the contacts open. The magnetic field in the ballast collapses rapidly producing an inductive kick, which establishes a current between the filaments and fires the tube into operation.

7. Cold cathode Requires high voltage in its operation. This lamp has electrodes made of thimble-type iron. It is not pre-heated and does not require a starter for starting. Special high voltage transformers operate it. Neon and mercury lamps are classified under cold cathode lamps .

8. Instant-starting, hot-cathode The lamp cathode in the instant-start is not pre-heated. Sufficient voltage is applied across the cathodes to create an instantaneous arc. As in preheat circuit; the cathodes are heated during lamp operation by the arc. The instant-start lamp require single-pin bases, are generally called slim line lamps .

9. Hot-cathode, rapid-start These are similar in construction to the preheat lamps; the basic difference is in the circuitry. This circuit eliminates the delay inherent in preheat circuits by keeping the lamp cathodes constantly energized (preheated). When the lamp circuit is energized, the arc is struck immediately.

10. Classifications of Fluorescent Lamp

11. Regular Fluorescent Lamp

12. Compact Fluorescent Lamp

13. Parts and functions of fluorescent lamp C:\Users\HP\Desktop\CLIFFORD\lessons\fluorescent lamp.pptx

14. Function of a Starter Current moves in utilizing the rare gas as conducting means and the rare gas produces a “glow”. The glow generates heat and causes the bimetallic blade to expand. When the bimetallic blade is heated, it changes shape and touches the fixed contact. The close contacts of the two starter contacts produce an easy path for the current to flow.

15. In common with all gaseous discharge lamps, the fluorescent must be provided with some device for limiting the current drawn by the discharge. Without a limiting device, the current would rise to a value that would destroy the lamp. A device or auxiliary called ballast can best meet this requirement. The ballast for operating lamps on an alternating current consists of a small choke coil woven on an iron core .

16. Important Functions of a Ballast: 1. It preheats the electrodes to make available a large supply of the electron. 2. It provides a surge of relatively large potential to start the arc between the electrodes. 3. It prevents the arc current to increase beyond the limit set for each size and lamp.

17. THE LIFE SPAN OF FLUORESCENT LAMP The life of fluorescent lamp is affected not only in the fluctuation of voltage and current but also by the number of times it is started. Electron emission material is “sputtered off” from the electrodes continuously during the operation of the lamp and in larger quantities each time the lamp starts. Many fluorescent lamps have a rated average life span up to 30,000 continuous burning hours but with an average of 3 hours burning per start, it could only last for 12,000 hours .