Lamba Fluorescent û Prînsipê Ya Kariyebûna Lamba Fluorescent

Fluorescent Lamp çi ye?

Yek fluorescent lamp yek lampê hêvdestbûr û ku bi fluorescence re çavkaniya derbasdar dihêve. Yek mercury vapour lamp da ku bi fluorescence re çavkaniya derbasdar dihêve. Yek electric current di gas de energîn da ku mercury vapor zanikê ultraviolet radiation bide ji bo discharge process û ultraviolet radiation hûn phosphor coating ê lamp inner wall vêşen çavkanî derbasdar bike.

Yek fluorescent lamp electric energy tê dihate werin guherandin be ser çavkaniya bikarhêner pêk hatine yên incandescent lamps. Luminous viability yekêm fluorescent lighting systems 50 der 100 lumens per watt e, ku pir kêmtir ê te dibe ku incandescent lamps bi light yield weha.

Fluorescent Lamp çimke çalak e?

Piştî ku biz çalakîya yek fluorescent lamp bigihînin, ewerina yek circuit ya fluorescent lamp an jî circuit ya tube light dikarin bigihînin.

Lê hêre ballast, switch û supply series bikin. Dibare fluorescent tube û starter across bikin.

• Herdemê ku biz supply ON bikin, voltage full di lamp û starter de bigihîne. Lê dema ku voltage full e, no discharge nayê, ya nîn lumen output ji lamp.

• Dema ku voltage full e, glow discharge yekên starter ê dibike. Ji ber ku electrodes gap di neon bulb de starter yekên fluorescent lamp yekên ku piç e.

• Gas inside starter bi voltage full ionized dibike û bimetallic strip înde. Wê bimetallic strip bend bikin û fixed contact connect bikin. Herdemê ku current start flow bikin, starter de flow bikin. Ionization potential neon yekên argon piç e, lê electrode gap small e, high voltage gradient di neon bulb de dibike û glow discharge yekên starter dibike.

• Herdemê ku current start flow bikin di touched contacts de neon bulb de, voltage across neon bulb get reduced bikin ji ber ku current, voltage drop di inductor(ballast) de bikin. Voltage across neon bulb de reduced û no voltage, no gas discharge dibike û bimetallic strip cool bikin û break away from fixed contact. Dema breaking of the contacts di neon bulb de, current interrupted bikin, û large voltage surge di inductor(ballast) de dibike.
  

  

• High valued surge voltage di fluorescent lamp (tube light) electrodes de dibike û penning mixture (mixture argon gas and mercury vapor) strike bikin.

• Gas discharge process dibike û continue bikin û current again path to flow through fluorescent lamp tube (tube light) itself. During discharging of penning gas mixture the resistance offered by the gas is lower than the resistance of starter.

• Discharge of mercury atoms produces ultraviolet radiation which in turn excites the phosphor powder coating to radiate visible light.

• Starter gets inactive during glowing of fluorescent lamp (tube light) because no current passes through the starter in that condition.

Physics behind Fluorescent Lamp

Herdemê ku voltage sufficiently high applied bikin di electrodes de, strong electric field set up bikin. A small amount of current through the electrodes filaments heats up the filament coil. As the filament is oxide coated, a sufficient amount of electrons is produced, and they rush from the negative electrode or cathode to the positive electrode or anode due to this strong electric field. During the movement of free electrons, the discharge process gets established.

The basic discharge process always follows three steps:

1. Free electrons are derived from the electrodes, and they get accelerated by the electric field applied.

2. Kinetic energy of the free electrons is converted into the excitation energy of the gas atoms.

3. The excitation energy of the gas atoms gets converted into the radiation.

In the discharge process, a single ultra violates spectral line of 253.7 nm is produced at a low pressure of mercury vapor. To generate 253.7 nm ultra violate ray the bulb temperature is kept between 105 to 115oF.
The length to diameter ratio of the tube should be such that fixed wattage loss happens at both ends. Where this wattage loss or glow of electrodes takes place is called cathode and anode fall region. This watt loss is very small.
Again the cathodes should be oxide coated. Hot cathode provides an abundance of free electrons. Hot cathodes, mean those electrodes which are heated by circulating current and this circulating current is provided by choke or control gear. Few lamps have cold cathode also. Cold cathodes have a larger effective area and higher voltage such as 11 kv is applied across them to get ions. Gas starts to be discharged due to this high voltage application. But at 100 to 200 V the cathode glow get separated from the cathode, it is called cathode fall. This provides a large supply of ions which are accelerated to the anode to produce secondary electrons on impact which in term produce more ions. But cathode-fall in hot cathode discharge is only at 10 V.

History & Invention of Fluorescent Lamp

• In 1852, Sir George Stokes had discovered transformation of the ultra violate ray radiation into visible radiation.

• From this time to 1920 various kinds of experiments had been done to develop the low and high pressure electric discharges in the mercury and sodium vapor. But all those circuitry developed were inefficient to transform the ultra violate ray to the visible ray. It was because; the electrodes could not emit sufficient electrons to establish arc discharge phenomenon. Again many of the electrons collided with the gas atoms and that was elastic. So the excitation did not create spectral line to be utilized. But very little work was done on fluorescent lamps.

• But in 1920s, a major breakthrough happened. The fact has been discovered that the mixture of the mercury vapor and inert gas at low pressure is 60% efficient to convert the electrical input power into a single spectral line at 253.7 nm.
  Ultra violate ray gets converted into the visible light rays by using appropriate fluorescent material inside the lamp. From this time fluorescent lamp got paved to be introduced in the people’s daily life.

• Later, Dr. W. L. Enfield in 1934 had received a report from Dr. A. H. Crompton about the use of fluorescent coated lamp. Immediately a research team had been created by Enfield and started to create commercial fluorescent Lamp. In 1935 their team had produced a prototype green fluorescent lamp that had efficiency about 60%.

• After two and half years later, fluorescent lamps have been introduced in white and six other colors in the market. Various mixture of phosphor powder is used to produce various colors from the fluorescent lamps. The first lamp had been introduced with 15, 20 and 30 W in 18 inch, 25 inch and 36 inch lengths.

• Sooner after 40 W T12, 4-ft lamp had been introduced and used widely in office, school, industry lighting. The early lamps gave the light somewhat yellowish to a 3500K. Later on, 6500K daylight lamps are developed in such a way that it produces a light to simulate an average north sky light on an overcast sky.

• Generally the 4 ft lamps, with 1.5 inch in diameter, 40 W were available in the market in 1940. But gradually design has been changed to its better utilization. In the arc, discharge portion of the lamps has been changed. But argon is still used though the pressure that is somewhat less than the previous pressure. The mercury vapor is maintained at that same pressure like previous. This lamp requires 425 mA with 100 to 105 V voltage drop.

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