College / Polytechnic

Syllabus Year

Branch Sem (x) IPT Session ID (xx)

Training Ref Number (xxx)

C 09 E 5 0 3 0 0 2

Halogen Lamps

Halogen Lamp Construction

The light is still produced by a coiled filament of tungsten. The filament is protected by a quartz or hard glass bulb which is deliberately small to ensure the correct bulb wall temperature. The bulb is filled with a halogen gas rather than nitrogen and argon. The halogen gas is either iodine or bromine, or in some cases a mixture of both. The bulb shape is tubular so it is close to the hot filament.

How they work: Current flows through a filament and heats it up,just as in

incandescent lamps. These lamps therefore generate a relatively large amount of heat. The halogen cycle increases the efficiency and extends the service life compared with traditional incandescent lamps

For mains and Low voltage operations

Longer service life and higher luminous efficiency than incandescent lamps

Applications : Domestic areas, Restaurants and catering

Fluorescent Lamps

Fluorescent Lamp Parts

Basically, a fluorescent lamp is made up of five components.

1. GLASS TUBE, coated on the inside with fluorescent powders called PHOSPHORS.

2. Two ELECTRODES (or cathodes) coated with EMITTER, supported by a glass mount structure, and sealed at the ends of the tube.

3. FILLING GAS - usually a low pressure of Argon or Krypton/Argon mixture. 4. Small amount of MERCURY (less than 20 mg), which vaporizes during the lamp

operation. 5. LAMP CAP cemented to each end of the tube to connect the lamp to the lighting

circuit.

Fluorescent Lamp Operation

When the circuit is energized, electricity heats the cathodes.. The cathodes are coated with material which, when heated, emits electrons. The electrons establish an electric arc between the cathodes at opposite ends of the tube. The electrons collide with the mercury atoms, causing mercury to emit invisible ultra-violet radiation. The ultra-violet is absorbed by the phosphor coating on the tube and re-radiated as visible light.

Fluorescent Lamp Caps There are three different types of lamp cap:

Single pin Bi-pin Four pin

Fluorescent Lamp Circuit Operation

Shows the basic fluorescent lamp circuit.

The circuit must contain a ballast to limit the current and a starter to provide the pre-heat conditions. Initially the starter switch closes so the two cathodes are connected in series. Current flows and the cathodes heat up emitting electrons. After a short time the starter switch opens so voltage is applied across the tube. If sufficient electrons are available an arc is struck and the starter plays no further part until the next starting operation. If there are insufficient electrons, the tube will flicker, fail to start, and the starter will repeat the heating of the cathodes. The ballast limits the current to a safe and appropriate level for the power of lamp. Without the ballast, the current would increase to a high level and the lamp would destroy itself.

Fluorescent Lamp Advantages 1. Fluorescent lamps are 3-7 times more efficient than incandescent lamps. 2. Power consumption for equal light output is much less than for an incandescent

lamp. 3. Rated lamp life is between 5,000 and 18,000 hours, depending on style,

approximately five to eighteen times longer than typical incandescent lamp life. 4. Available with wattage ratings from 4 to 125W.

.

Fluorescent Lamp Disadvantages 1. Variations in supply voltage affect lamp light output and starting. 2. Required external equipment (ballast) consumes energy, adds to equipment

cost. For retro- fits, establishes lamp size and wattages that can be used. 3. Lamp frequency flicker can cause discomfort to some people. 4. Operation on a range of supply voltages requires different control gear

components or more expensive tapped ballasts. 5. Lamps are large for the amount of light produced - HID and incandescent lamps

are much more compact.

6. Radio frequency interference from lamps may disturb communications equipment at close range. Note there are new EMC (Electro Magnetic Compatibility) Regulations due to come into force for the EU.

7. Distracting lamp flashing can occur with a glow starter attempting to strike a failed lamp.

Q & A Fluorescent Lamps

1. Standard fluorescent lamps contain a filling gas that is usually ___________________ or _____________________

2. Electrons collide with mercury atoms and cause the emission of ______________________________________

3. What happens when the cathodes are heated? a. _____________________________________

4. What is the purpose of the phosphor coating? _______________________________________

5. When a starter is pre-heating the cathodes, they are connected in ________________________

6. Instant start lamps with single pin caps are called __________________________

7. . What is the most common diameter of fluorescent lamp today ____________________________

8. What is the main function of a fluorescent lamp ballast? __________________________________________

9. List four advantages of fluorescent lamps. ___________________________ ___________________________ ___________________________ ___________________________

10. Fluorescent lamp efficacies are typically _______times higher than incandescent lamps

11. Which gas is contained in fluorescent lamps? (Transport - Dangerous Goods)

12. Can fluorescent lamps also be operated at 60 Hz?