ELECTRIC LAMPS – PART – 08 - OPERATION OF METAL HALIDE (MH) LAMPS

INVENTOR OF METAL HALIDE (MH) LAMPS

In the year 1912 Charles P. Steinmetz was the first to use halide salts in a mercury vapor lamp. In the year 1962 Robert Reiling developed the first reliable MH lamp. Reiling built on the work of Steinmetz to complete his work. The MH lamp became more popular, and decades later the price of the lamp became more affordable. MH is very popular due to its good quality white light and good lamp efficacy.

METAL HALIDE (MH) LAMPS

MH lamps are similar in construction to HPMV lamps but in addition to mercury, a number of iodides [Iodide means a salt or ester of hydriodic acid] are added which fill the gaps in the light spectrum and these lamps are operated at higher temperatures and pressures. Iodides are used to improve the colour characteristics of light.

HALIDE

A Halide is a chemical compound of a halogen combined with an electro-positive element. A halogen is a monovalent element which readily forms negative ions. There are five halogens: fluorine, chlorine, bromine, iodine and astatine.

CONSTRUCTION OF MH LAMPS

1. It consists of two glass tubes, two main electrodes, one

    auxiliary electrode, a ballast and a capacitor. 

2. Outer glass tube is made up of Borosilicate glass which is     

    used for insulation as well as to block the UV radiation

    coming from the arc.

3. Inner tube (discharge) is made up of quartz or hard glass and

    contains a starting gas (usually argon), mercury and MH

    salts.

4. Filaments are made up of tungsten treated with radioactive

    Thorium.

5. Molybdenum is used in sealing discharge tube as it does not

    expand even under extremely high temperatures.

6. Molybdenum is highly resistant to corrosion and is also used

    in high strength steel, armor and electrical contacts.

7. MH lamps have a coated finish on the inside of the bulb that

    diffuses the light.

8. Often a phosphor coat is used in diffusing light as well as

    changing the lamp's colour properties.

9. Choke is provided to develop a high voltage at the time of

    starting and to limit the current after discharge.

10. Capacitor is connected across the supply to improve the

    power factor.                                                                                                                                                                       
HALIDE 'SALTS' USED IN THE MH LAMP

AgCl (Silver chloride)       – white light

AgF (Silver fluoride)         - No color

AgBr (Silver bromide)       - pale yellow

Agl (Silver iodide)            - green yellow

OPERATION OF MH LAMP

1. When the lamp is cold, the halides and mercury are

    condense on the fuzed quartz tube (discharge tube).

2. When supply is switched ‘ON’, current passes through the

    starting electrode and jumps to a short distance leading to

    the main electrode.

3. Argon is used to start discharge in the lamp and argon gas

    strikes and initiates an arc at low temperature.

4. After the arc initializes, the tube heats up and the mercury

    is vaporized.

5. The initialized arc activates to work through the resistance of

    the gas, during this period, more molecules of the gas

    become ionized.

6. This creates more electric current to pass through the tube,

    allowing the arc to become wider and hotter.

7. This heat produced by the arc in the tube vaporizes the solid

    mercury and travels through the mercury vapor to

    reach the other main electrodes

8. There is less resistance on this path now and current stops

    flowing through the starting electrode.

9. After a mercury vapor arc strikes and heats, the halides

    vaporize and gets separated.

10. The metal atoms diffuse away from the arc to cooler areas

    and recombine with the halogen before they damage any

    part of the electrodes and the lamp is now fully warmed up

    and produce its white light.

TYPES OF METAL HALOIDE LAMPS

A variety of shapes are available  

(i) Elliptical                    
(ii) Tubular

(iii) Double Ended and   (iv) Compact Pin ended and reflector.

ADVANTAGES

1. More pure white light than the popular HPS lamps.

2. More energy efficient than mercury vapor lamp.

3. Lumens per wattage range from 65 to 115.

4. Life time is 20,000 hrs for mounted base up and 10,000 hrs for

    horizontal mounted lamps.

5. Colour Rendering Index is 60 - 90 (depends on brand and

    chemical compositions)

DISADVANTAGES

1. Very high manufacturing cost.

2. The light is very bright and it produces much more light

    pollution than HPS lamps, since the whites from an MH lamp

    are closer to daylight in frequency.

3. Warm up time is 1 - 15 minutes.

APPLICATIONS

1. These lamps are suitable for flood-lighting, industrial

    lighting and public lighting.

2. Outdoor lighting where good colour rendering is needed.

3. Television/film lighting, sports fields, car headlights, heavy

    flashlights and green house applications.

ELECTRIC LAMPS – PART – 07 – OPERATION OF HIGH PRESSURE MERCURY VAPOUR LAMP

INVENTOR OF MERCURY VAPOUR (MV) LAMP

John Thomas Way (London) developed a mercury vapor lamp in

the year 1860. He tested them on the Hammersmith Bridge in London.

The modern high-pressure mercury vapor lamp is developed in the year 1936 by Philips (Nederland) No individual names are available.

The mercury vapor lamp is a High Intensity Discharge (HID) 

Lamp and it is also called as hot cathode gas-discharge lamp.

HPMV lamp is similar in construction to the sodium vapour lamp and may have low pressure in the bulb.

A high pressure (1 to 2 atm) mercury vapour lamp has amount of mercury introduced in the lamp.

A recent development in HPMV lamps in an ultra-pressure lamp operating at about 40 atmosphere and its efficacy is more than the sodium vapour lamps.

CONSTRUCTION

1. It consists of a discharge envelope enclosed in an outer bulb

    of ordinary glass.

2. The discharge envelope may be of hard glass or quartz.

3. The space between the bulbs is partially or completely

    evacuated to prevent heat loss by convection from the inner

    bulb.

4. The inner bulb consists of argon and a certain quantity of

    mercury and outer tube is coated with fluorescent material.

    [Argon is introduced for initial discharge of the mercury]

5. The outer bulb absorbs harmful ultra violet rays.

6. This lamp consists of two main electrodes and one auxiliary

    electrode.

7. The main electrodes are made up of tungsten wire in the

    shape of helixes and it containing a coating of elements of

    thorium material (electron emitting).

8. An auxiliary or starting electrode is connected through a high

    resistance.

9. A choke coil having different tapping is connected in series

    with the lamp to give high starting voltage for discharge and

    for controlling the current and voltage across the lamp after

    discharge.

10. A capacitor is connected across the supply to improve the

     power factor.

OPERATION

1. When the supply is switched on, full main voltage is applied

    between the auxiliary electrode and neighboring main

    electrode.

2. When the tube is filled with mercury vapor, low resistance

    path is created and arc shifts between main electrode and

    discharge tube.

3. Current does not flow through the main electrodes due to

    high resistance of the gas.

4. However the current starts to flow between the main

    electrodes and the auxiliary electrode through the argon gas.

5. This breaks down the gap and a discharge through the argon

    takes place.

6. This enables the main discharge to commence.

7. The discharge from the tube strikes the fluorescent coating

    of outer bulb from which secondary emission starts and gives

    crisp white color light.

8. The vapour pressure rises until all the mercury is vapourized

    when the light given out is with a bluish tinge (tinge means

    a slight but appreciable amount).

9. This lamp is like a fluorescent lamp, requires a ballast

    designed for its specific use.

10. Special ballasts are required for dimming.

ADVANTAGES

1. Color rendering is better than that of high pressure sodium

    street lights.

2. Long life (16,000 to 24,000 hours).

3. It produces similar to day light which may help in increasing

    the production of a factory.

DISADVANTAGES

1. HPMV Lamps are the most inefficient source of light, with an

    efficacy in the 25 to 55 lumens per watt range.

2. HPMV lamps may be greatly affected by lamp lumen

    depreciation and should be replaced after 24,000 hours.

3. Four to five minute cooling and restart time is needed.

4. Like many lamps it contains traces of mercury which must

    be disposed of properly.

5. It takes 6A approximately when switched on and after six

    minutes it falls to 3A.

APPLICATIONS

1. These lamps are suitable for large areas like parks, street

    lighting, high ceiling buildings, and gyms.

2. MV lamps have found greatest use in industrial applications

    and outdoor lighting.

3. Lamp sizes range from 40 to 1,000 watts.

ELECTRIC LAMPS - PART - 06 - OPERATION OF HIGH PRESSURE SODIUM VAPOUR LAMP

INVENTORS OF HIGH PRESSURE SODIUM VAPOUR LAMP

A researcher named Robert L. Coble working at the General Electric Research Lab developed a material called Lucalox. 

Lucalox was a commercial term for aluminum oxide ceramic.

His work helped pave the way for William Louden, Kurt Schmidt, and Elmer Homonnay to invent the HPS lamp.

General Electric first developed this lamp and it came on the market in 1964.

The lamp is an improvement over the LPSV lamp in that it has more acceptable colour with the great efficiency of the sodium lamp.

The better color rendering comes with a bit of sacrifice, it has less efficiency than the LPSV lamp.

CONSTRUCTION AND OPERATION

1. High pressure sodium (HPS) vapour lamps are smaller than  

    LPS lamps.

2. High Pressure Sodium Vapour lamps with a polycrystalline

    translucent aluminum oxide discharge tube enclosed in a

    tubular outer glass envelope.

3. The discharge tube is internally coated with aluminum oxide

    powder.

4. The discharge tube contains an amalgam of mercury and     

    sodium along with xenon gas.

5. Xenon is a colorless, dense, odorless and noble gas that

    occurs in the Earth's atmosphere in trace amounts.

6. The outer shell is evacuated and a better maintains this high

    degree of vacuum throughout the lamp life.

7. These lamps need a control gear comprising of ballast, ignitor 

    and capacitor for optimum performance.

8. They produce a dark pink glow when first struck, and a

    pinkish orange light when warmed.

9. Some lamps also briefly produce a pure to bluish white light

    in between.

10. This is formed by the mercury glowing before the sodium is

      completely warmed.
                                                   

ADVANTAGES

1. Very high lamp efficacy hence highly energy efficient.

2. Long life and low light depreciation.

3. Very high lumen output.

4. Golden white light admitted by lamps gives a warm

    appearance and better visual acuity.

5. Ideally suited for fog, dust rainfall conditions.

DISADVANTAGES

1. The light produced is a golden white color, which may not

    be appropriate for certain applications.

2. Requires a ballast.

3. Once started can take from five to ten minutes to reach full

    light output

4. They also require at least a one minute cool-down to re-

    strike.

5. End of life is characterized by on-off-on cycling, and

    continued operation can damage the lamp ballast if not

    replaced quickly.

APPLICATIONS

1. It is 7 times as efficient as incandescent lamp.

2. Ideally suitable for reducing energy consumption in both

    indoor/outdoor applications.

3. Suitable for Highway streets, flyovers, junctions etc.

4. Airport apron's parking areas, storage yards, docks etc.

5. Industries warehouses, goodness etc.

6. Floodlighting of monuments, exhibition sites etc.

7. Long lamp life - 24,000 hours.

8. Excellent lumen maintenance.

9. Wide range of lamp types with wattages ranging from 35 to

    1000 watts.

10. Most HPS lamps can operate in any position.

ELECTRIC LAMPS - PART - 05 - OPERATION OF LOW PRESSURE SODIUM VAPOUR LAMP

LOW PRESSURE SODIUM VAPOUR LAMP

These lamps were invented first in 1920 by ARTHUR H. COMPTON at Westinghouse, USA. It is a gas-discharge lamp that uses sodium in an excited state to produce light.

WORKING PRINCIPLE

It works by electric discharge (passage of electricity through sodium vapours at low and high pressure) filaments of the lamp sputter (sputter means spit up in an explosive manner) fast moving electrons, which hit the sodium atoms (vapour) causing the valence electrons of the sodium atoms to excite to higher energy levels and the electrons thus excited and are emitting the characteristic monochromatic bright yellow light (589 nano-metre).

CONSTRUCTION

1. A Low-Pressure Sodium (LPS) vapour  lamp contains an inner

    discharge tube made of borosilicate glass that is fitted with

    metal electrodes and filled with neon and argon gas and a

    little metallic sodium.

2. Neon gas serves to start the discharge and to develop enough

    heat to vaporize the sodium.

3. Argon has a lower glow voltage, argon helps the smaller

    lamps start at a lower voltage.

4. The sodium vapour lamp is only suitable for alternating

    current, and therefore requires choke control.

5. A voltage of the order of 380- 450 volts (depending on the

    wattage) is necessary to start the discharge, which is

    obtained from a high reactance transformer or an

    auto-transformer.

4. Its operating power factor is low (0.3) hence suitable

    capacitor must be used to improve the power factor.

OPERATION

1. When the lamp is not in operation, the sodium is usually in

    the form of solid deposited on the side walls of the tube.

2. When it is connected across the supply mains, current passes

    between the electrodes, it ionizes the neon and argon,

    giving a red glow until the hot gas vaporizes the sodium.

3. The discharge tube is U-shaped. When the lamp is turned on

    it emits a dim red/pink light to warm the sodium metal and

    within a few minutes it turns into the common bright yellow

    as the sodium metal vaporizes.

4. LPS lamps have an outer glass vacuum envelope around the

    inner discharge tube for thermal insulation, which improves

    their efficiency.

5. At starting it creates a red glow due to the neon gas and the

    neon gas lights at a lower temperature.

6. As the temperature increases the sodium begins to vaporize

    and the lamp turns to a pure yellow, which makes objects

    appear as grey.

ADVANTAGES

1. Most energy efficient light source commercially available,

    with an efficacy of 100 to 185 lumens per watt.

2. Lamps have average life in the 14,000 to 18,000 hour range

    and have excellent lumen maintenance (very little reduction

    in lumen output over life of lamp).

3. Most lamps will restart immediately after interruption of

    power supply, but require some time to come up to full

    brightness.

4. Provides superior uniformity of light distribution over all HID

    lamps.

5. Lumen output does not drop with age.

6. High lamp efficacy leads to low energy consumption.

DISADVANTAGES

1. These lamps have poor color rendering characteristics.

2. It is almost impossible to distinguish colors under an LPS lamp

    because light produced by this source is monochromatic (a

    single color).

3. Most expensive lamp to install.

4. Run time to full light output is the longest (7 to 10 minutes).

5. Require special disposal considerations.

    [Care should be taken in handling these lamps, particularly,

    when replacing inner U tube. If it is broken, then sodium

    comes in contact with moisture, fire will result]

APPLICATIONS

1. Road lighting and railway marshalling yards

2. Airports, harbors and ports and, quarries, foundries and

    rolling mills.

3. Security and orientation lighting.

ELECTRIC LAMPS – PART – 04 – OPERATION OF NEON LAMPS OR COLD CATHODE FLUORESCENT LAMPS [CCFL]

INVENTOR OF NEON GAS

The name neon is derived from the Greek word, neos, meaning new.

Neon was discovered in 1898 by the British chemists Sir William Ramsay and Morris W. Travers in London, England.

Neon is chemically inert and forms no uncharged chemical compounds.

It is a colorless, odorless, inert monatomic gas under standard conditions, with about two-thirds the density of air.

Neon is commercially extracted by the fractional distillation of liquid air and it is considerably more expensive than helium, since air is its only source.

INVENTOR OF NEON LAMP

1917 Daniel McFarlan Moore made his mark on lamp history by inventing the negative glow neon lamp.

He developed small bulbs with two electrodes, neon gas glows immediately around the electrodes.

This is used as indicator lights on many devices.

It is still used in decorative Christmas lights since the red light flickers and dances between electrodes similar to a flame.

A neon lamp (also neon glow lamp) is a miniature low pressure cold cathode (gas –discharge) lamp.

The term "Neon Lamp" is used to describe a CCFL with a tube diameter less than 15 millimeters.

PRINCIPLE OF OPERATION

1. A neon lamp is a sealed glass tube filled with neon gas.

2. There are electrical terminals at either end of a neon tube.

3. When the tube is switched off, it contains ordinary atoms of

    neon gas (red circles).

4. Rig the terminals up to a high-voltage power supply and

    switch on, for pulling the neon atoms apart.

5. Some of the atoms will lose electrons to become positively

    charged ions (big blue dots).

6. Being positively charged, these neon ions will tend to move

    toward the negative electrical terminal.

7. The electrons the neon atoms lose (small blue dots) are

    negatively charged, so they hurtle the opposite way toward

    the positive terminal at the other end of the tube.

8. In all this rushing about, atoms, ions, and electrons are

    constantly colliding with one another.

9. Those collisions generate a sudden smash of energy that

    excites the atoms and ions and makes them give off photons

    of red light.

10. So many collisions happen with such rapidity that we get a

      constant buzzing of red light from the tube.

COLOURS

1. Clear red – Red opaque - Neon Gas with red phosphor

2. Blues, Greens and Yellow – Phosphor with Argon and

    Mercury Gas [Argon starts the arc, warms up, then mercury

    gas ionizes, UV light is emitted] UV activates the colored

    phosphor.

3. Pinkish white and white – Helium gas in a clear tube, or Hg

    vapor with a white phosphor.

4. Orange – Neon Gas with yellow phosphor.

5. Whitish-Green – Krypton

6. Bluish-white – Xenon

THERE ARE TWO TYPES OF CCFL

TYPE – 01 – NEON LAMPS - Neon lamps are used in indicators, night lamps and polarity testers. They are generally of 5 watts.

1. They consist of glass bulb filled with neon gas.

2. They give orange pink light.

3. The electrodes are made of iron or steel and are spaced a

    few mm.

4. The lamp efficacy lies 15 – 40 lumen per watt.

5. A series resistor is connected in series to control the

    magnitude of current. [Electrical tester]

TYPE – 02 – NEON TUBES – These tubes are not used for lighting purpose, but these are used for advertising purposes as neon-signs and letters. 

1. Neon tube with varying lengths are employed for advertising

    and decoration purposes.

2. These lamps are called as cold cathode lamps because its

    operating temperature is 200 degree centigrade.

3. The tubes are mounted either on a wooden frame or metal

     base.

4. The tubes are matched with step-up transformers.

5. The electrodes are made of iron, steel or copper in shape of

    round and are housed at the two ends of the tube which is

    filled with neon gas and connection between letters are

    made by nickel wires.

6. The step up transformer secondary is grounded at the mid-

    point for safety.

7. The length of the tube may vary from 2 to 10 metre.

8. They be bent into any desired shape during manufacturing.

9. The diametre of the tube may be of 10, 15, 20 and 30 mm

    with current of 25, 35, 60 and 150 milliamps.

10. The voltage required is 500 V to 1000 V per metre of the

      tube length.

11. Twice the operating voltage is required for starting.

12. Capacitors are used to improve the P.f. which are placed

      on the low voltage side of transformer.

13. The capacity of the transformer should be of 50 to 100 VA.

14. The transformer is made in a special manner with a      

      magnetic shunt. As the tube warms up, its resistance

      decreases and the current increases and an ordinary     

      transformer cannot serve the above purpose.

15. The average working hours of neon tube is about 10,000

      hours.

ADVANTAGES

1. To obtain different colors different substances are added

    with neon gas.

2. Good lumen per watt.

3. More reliable than LEDs for airport runway landing lights.

DISADVANTAGES

1. The shape of tube is a limitation.

2. It gives only diffused light (not good for any focused beam

    applications).

3. Argon is not reliable in cold temperatures.