(A) Vacuurn Lamps : These lamps can operate upto the temperature of 2000°C. The construction is shown in Fig. 2.2. The filaments used for this type of lamp are carbon, osmium, tantalum or tungsten. Tungsten is best of all. The filament materials have the following properties : () High melting point. (i) Low vapour pressure. (iii) High resistivity. (iv) Low temperature coefficient. ()_ Ductile. (vi) Mechanical strength. The bulb is evacuated so that filament is not oxidized even at higher temperatures, Melting point of tungsten is 3400°C. The filament heats up immediately and its resistance increases immediately. Its luminous efficiency is 10 lumens/watt. As the time passes, aging of tungsten starts and its efficiency decreases. The total depreciation of light output is roughly 15% over the useful life range. There is effect on the performance of the lamp |. 2.2: Vacuum/Gas due to voltage variations. 5% increase in voltage Filled Incandescent Lamp increases lumens output by 20% but shortens the life by 50%, 5% decrease in voltage reduces 20% lumens output but increases the life of lamp by two times. The normal life of filament lamp is 1000 working hours. Advantages : Operating power factor is unity. Operates directly on normal voltages. Good radiation characteristic in luminous range. Available in various shapes and sizes. Rating 15 watts, 25 watts, 40 watts, 60 watts, 100 watts, 200 watts and 500 watts. Very cheap in cost. 7. Handy and easily fixed up. (8) Gas Filled Incandescent Lamps (Construction is same as type A) ‘A metal filament can work in an evacuated bulb upto 2,000°C without oxidation and if it is worked beyond this temperature it vaporizes quickly and blackens the lamp. For higher efficiency it is necessary to use working temperature more than 2,000°C keeping down the evaporation, which is possible by filling the bulb with an inert gas-argon with a small percentage of nitrogen. Nitrogen is added to reduce the Possibility of arcing. Krypton is the best gas for this purpose but it is so expensive that it is used only in special purpose lamps, such as miner lamps. The tungsten filament can safely be burn at a temperature of 2,400°C to 2,750°C according to the size of the lamp. However, due to presence of gas there is heat loss due to convection currents. This loss depends upon the surface area of filament. As such, coiled coil filaments, which take much less space compared with coiled filaments are used with such lamps. A coiled coil filament is made by winding tungsten wire on a fine iron wire to form a spiral which is again wound on to a thick iron wire to form a coiled coil (iron is later on dissolved out by acid). Helical filaments also have a slower rate of tungsten evaporation. This evaporation eventually causes bulb blackening because the tungsten vapour condenses as a black film on the inner surface of the bulb. In a gas-filled lamp, the hot gas carries ae eeneza b instead of spreading © the bulb instead of spreading the tungsten vapour upward. Therefore, a black spot form: 1s are often placed inside the oe the entre inner surface, sina high-vacuum bulb. Chemicals led BET ecw of wire mesh ca to capture tungsten vapour and thereby reduce the rate Of BUCCI ces of tungsten van collector grid may also be attached to each lead in wire tO , K Efficiency of coiled coil lamp is about 12 lumens/watt. snvoduetion of gas 1 ore thn in meg, For low wattage lamps, however, the heat oss due to inocu m wattage lamps, so for low wattage (upto 40 watts), vacuum tyP* Blumination and Electrification of Bulldings (Sem. . is at the top OF (a) Coiled filament (b) Coiled coil filament Fig. 2.3 mes 2.2 ARC LAMPS s a The basic principle : Two electrodes touching to each other are o electrodes © ‘connected to the source of electricity as shown below. Both are carrying Currents, Refer Fig. 2.4 (a). ' o * If now electrodes (1) and (2) are separated a bit, even then they carry 4 an electric current and in the gap separation an ‘arc’ is formed. Fig. 2.4 (0) ” i ‘lectrodes * Inthe gap, the arc has tremendous heat and temperature and light is @ ® Produced as shown in the following Fig. 2.4 (b). * On this principle different arc lamps are designed. 1 . Md arc lamps are (i) carbon arc, (ii) flame arc or (iii) magnetic arc Fig, 2.4 (b) PS. 2.2.1 D.C. Carbon Arc Lamps Ql. Explain with neat sketch the working of carbon arc lamp wi In this type, carbon electrodes are used. © This is the old type lamp. ® ®@ TL - D.C. supply zs & () Fig. 2.5: D.C. carbon are lamp Two electrodes (1) and (2) placed touching to each other face tof inFi Rees 0 face are as shown in Fig. 25 (2) When current flows, rods soon become incandescence due to high rex; P . to high Now if they are sight pulled, so that @ gap of about 3 aie of carbon. forme! between them in the gap and a white light is producer m sotmed: an arab * Transfer of carbon particles from one rod to the other rote " ler rods maintait ii * Due to transfer of particles of carbon the positive rod after son eee low ant negative rod becomes as a pointed pencil as shown in Fig. 25 (b), aide amecomies De * Both rods burn out after some period. The rate of i So cross-section of positive rod is ma ¥ burning of positive rod is twice the negative de twice of the cross section of negative rod.lumina A.C. Carbon Arc mp: ‘* Inits case, burning of both positive and negative ro same in A.C. operation. ‘Since the carbon is consumed during operation, frequent adjustment for the gap between the rods is required. ‘An automatic device is provided for feeding the carbon into the arc for big lamps. © Requirement of voltage : V = (39 + 2.8) where [: length of the arc in mm. # Aseries resistance as shown in Fig. 2.3 is used for stabilizing the arc. © Overall luminous efficiency is very low which is 12 Lumens/watt. * In AC. arc lamp instead of a series resistance, inductor is used for stability. . o © % Production of light : : 85% of light by positive carbon, 10% of light by negative carbon. 5% of light by the air. * Temperature of positive carbon is about 3500°C to 400°C and that of negative carbon is about 2500°C. Uses of Arc Lamps : L. Cinema projectors. 2. Search lights. 2.2.3 FI ‘same and hence their cross-sectional area is Arc ‘* The principle of operation is similar to that of carbon arc lamp. * The electrode of such a lamp has 5 to 15% fluoride (called the flame material), 85 to 95% carbon. © Generally core type carbon electrodes are used, the cavities are filled with fluoride. © The fluoride has a characteristic which radiates light energy efficiently from a very high heated arc stream. ‘* Fluoride turns into vapour along with carbon. * Vapours cause a very high luminous intensities. * In addition to fluoride, there are some other flame materials. © Different flame materials which . ye produce different colours. © * Most of these colours do not appeal to eyes at the same time they produce strain on them. 2 * The arc can be drawn out to one Fig. 2.6: Flame are lamp side with the help of a magnet. * Though arc is very efficient but owing to objection to its colours, it has now been superseded by the electric discharge lamps. * The luminous efficiency of such a lamp is 8 lumens per watt. Magnetic Arc Lamp * In such a lamp, positive electrode made of copper and negative electrode made of magnetic oxide of iron are used. © The arcis struck in the similar way as in case of carbon arc lamp, such lamps are rarely used.1. Principle cent tube light. Tromagnetic radiations Of particu: it some other length. and persist j, Q1. Explain with neat diagram, "When fluorescent materials are subjected t> elect wavelength, they get excited and in turn gives out radiations giving out radiations even if exciting radiations are removed’ - sure mercu Basic operation : Fluorescent lamp, in principle is 1ow pres internal surface coated with suitable fluorescent material Tube contains argon or krypton gas to ease starting with small quantity of mercury under low pressure. At start current is passed through filaments which get heated up and emit electrons which strike mercury to give out radiations which fall ‘on fluorescent material thus emitting light. Tube contains argon gas in small amount in vapour form and mercury in globular form i.e. not in pure vapour form. Argon gas is used to initiate the arc. Circuit diagram for fluorescent lamps with : (a) Glow type starter (b) Thermal type starter. (a) Glow type starter : * In circuit diagram, R and C are used for protection purpose : R_ — is to avoid welding of starter contacts and C — Starter is made of two electrodes E: and Ez out of which E, is fixed and E2 is of bimetallic strip. They are fitted into a glass tube having helium and hydrogen at low ee st pressure. Normally, the contacts E, and E; are open and when supply is applied, full voltage is received by glow switch, this voltage is Fixed nee sufficient to start glow discharge between electrode et low pressure bimetallic strips E, and £; and heat generated bends E; to make contact with E, thus completing main circuit through choke Fig. 2.9 and lamp electrodes A and B. Current starts flowing through A and B and are heated in incandescent and argon gas which is in immediate vicinity is ionized, by this time glow is shorted out and so E; and E, cools and contacts open again. Sudden rate of change of current induces a voltage surge of about 1000 V across choke ard itiates a discharge of argon gas and heat is produced. This heat is sufficient to vaporizé mercury and potential difference falls to 100 to 110 V. ry discharge lamp wiy Visible light Fig. 2.8 : Tube with Glow Starter is to reduce radio interference. 1 | | | | | |(b) Thermal type starter : « Two bimetallic strips are initially closed so that current flows through filaments, heater coil, thus the electrodes A and R are heated to incandescence and argon gas is ionized. © Meanwhile, one of the bimetallic strip near to heater coil gets heated and bends thus interrupting filament current producing inductive voltage surge across electrode; establishing discharge through mercury vapour. * Starting time is very much less than the flow type starter. 5, Choke exclusively performs two functions : * Supply large potential for starting arc. ‘* Limit are current to a safe value. Fig. 2.10 : Tube with Thermal Starter Advantages : «If condenser is connected across surplus, efficiency is about 90.5%. Its life is three times more than filament lamp. * Ithas low surface brightness — so less glare and it casts soft shadow. Disadvantages : «High initial cost due to use of choke and starter. «Available in small wattage rating than incandescent lamp. Rating of fluorescent lamps ~ 20 watts, 40 watts, 65 watts, 80 watts. Note : Low ambient temperature increases starting time of fluorescent lamp. 2.3.1 Fault Finding in Case of Fluorescent Lamy Table 2.1 Type of fault Reasons Actions of repairs 1. Tube does not start. 1. Defective and loose holders. | 1. Turn tube through 90°. Try 2. Defective starter. another starter and check 3. Defective choke. connections. 4, Defective tube. 2. Replace starter. 3, Replace choke. 4, Replace tube 2. Sometimes end of a tube | Short-circuited starter. Check starter and replace. femain lighted. 3. Blinking ON and OFF. 1. Wrong connections. 1. Check all connections. 2. Loose contact. 2. Check all connections. 3, Voltage is low. 3. Change ballast tapping if required. 4. Defective starter. 4, Replace starter. 5._Defective tube. 5._Replace tube. ++ (Contd)Mumination and Electrification of Bulldings (Sem. ns Type of fault pene yoltage- ‘4. Blackening of the end Too low or too hig) portion. 3. Dark streaks along lamp. _ | Mercury globules. oie 6. Burn out electrodes. ‘Control unit in circuit or ct | shortccrcuted nar | Replace starter oF ballast. In cas 7. Snaking spiraling Insufficient heating due eae of new lamp, (with glow type of starter) | starter sparing ae ils it cures after few days. mi ‘Actions of repairs and Fluorescent Tubes Table 2.2 Fluorescent Tubes Tungsten Filament Lamps iminous efficiency increases with ty - id increase in length o 1. Luminous efficiency increases with the increase in voltage of the lamp. increase in wattage an tube. it does not give light close to natural lig 2. It gives light close to natural light, therefore, objects are properly seen. 3. Voltage fluctuation has comparatively more effect on the light output. 4. Luminous efficiency of coloured filament lamps is poor because coloured glasses are used for this purpose. therefore, colour rendering is defective. Voltage fluctuation has comparatively low effect on light output as the variations in voltage are absorbed in the choke. Different colour lights can be obtained by using different composition of fluorescent powder. Hence, efficiency is high and better colours are obtained. 5. Due to comparatively high working temperature, Due to low working temperature, heat radiation is low. heat radiations are also present. 6. Due to aging, light output is reduced. Due to aging, light output is gradualy reduced. Brightness is more. 8 Though the life of filament lamps varies with the working voltage, however, its normal life is 1,000 working hours, Brightness is less. life of fluorescent tubes is not affected 50 much by variations in voltage but it depends on the frequency of starting. The life of the tube is about 7,500 working hours. 9._No stroboscopic effect. 10. Cheaper in cost. 11. For same lumens output, more lamps are required and wiring cost is more. Life of the lamp is also less. Hence, overall cost of maintenance is more. 10. aa It has objectionable stroboscopic effect. _| Its cost per tube is more. For same lumens output, lesser number of tubes is required, the wiring cost is low. Sinct.| its life is comparatively more, replacement) = is low. Hence, overall maintenance cost 8= 7.4 TYPES OF OTHER LAMPS 2.4.4 High Pressure Mercury Vapour Lam, 1. Principle “When mercury discharge under low pressure gives mainly ultraviolet radiations. If pressure is increased to one or two atmospheres, its proportion of radiations in visible spectrum is increased and we get light having bluish tinge”. 2. Construction and Working : I consists of two tubes. Inner tube contains neon or argon gas under low pressure, two main electrodes in the form of oxide coated coils and starting or auxiliary electrode near the cap end side of main electrode, Inner tube is made of hard glass and in an evacuated outer tube, which maintains high ‘operating temperature of the inner arc tube. When supply is given, electric field is setup between the starting electrode and the adjacent main electrode. This causes discharge first to take place between them through limiting carbon resistance. This discharge through argon gas vaporizes all mercury and for the lamp to reach full brilliance requires 4 to 8 minutes depending upon the design. Auxiliary ‘electrode Outer Neon or ar ube Main electrode @ Fig. 2.11 : Construction of High Pressure Mercury Vapour Lamppath is created for current to floy istance ; ae ee des, Path of starting electrode ur + Once are tube i filed with mercury vapour a low resstones Pe between the main electrodes. The arc then s! tomatically becomes inactive eovy mercuty ion . ecvodes ve kept in electron emitting condition by the bembartimet of ah mere ms 7 a * Should the lamp go out while in services, it will not restart till Lisi Se Jow enough to allow for restarting of discharge between ey Sal 3. Mercury disacharge lamps are made in five sizes viz. 80, 125, 250, Serene In case of mercury vapour lamps, magnitude of the striking voltage ambient temperature Efficrency of ae lamps is of 30 to 40 lumens/watt and life is about 5000 mr Paaieese iar 6 Application : These are used for high ceiling manufacturing bays eee ee ae fee ing, sports grounds, garages and petrol station lighting, railway marshalling ya EZEW) Mercury todide Lamps © Construction is same as that of the HPMV lamp. * In KPMV lamp only mercury is added whereas in mercury io todides are added for filling the gap in light spectrums to imy ‘so produced. ‘= As compared to HPMV lamp, its efficiency is higher (70 to 90 lumens/watt). . fi ‘* In HPMV Lamp for ignition only choke is used whereas in mercury iodide lamp, choke as well as a separate ignition device is used. .dide lamp mercury and also number of prove the colour characteristic of light 1. Good light quality. 2, Higher efficiency (70 to 90 lumens/watt). 3. Better performance. 4. Ignition is effective. Applications : 1 In the fields of flood lighting. 2. Industrial fighting. 3. Public lighting. [2.4.2 Comparison of HPMV Lamp and Mercury lodide Lamp, Table 2.3 HPMV Lamp Mercury Iodide Lamp 1 Construction is same. 1._Construction is same. Filing gas is Hg. 2._Hg + iodides. 3__ Luminous efficiency is 60 to 65 lumens/watt 3.__Luminous efficiency is 70 to 90 lumens/watt. [4 tgnnion facility choke onl 4,_Choke and additional ignition device. 5. Cost moderate. 5.__More than HPMV lamp. 6. Used in street lighting, stage lighting, sports| 6. Used for flood lighting, industrial lighting, ground garages and petro! station lighting, Public lighting. railway marshalling yards, park lighting 2.4.3 Sodium Vapour Discharge Lamp) 2. Principle : “Electrons are emitted from cathode by subjecting the surface of the cathode to very high electric stress so that electrons are forcibly ejected from orbits of atom against nuclear centripetal force". |Bhumination and Electrification of Buildings (Sem.V) 2.12 Typeset ts 2 «+ Ttconsets of inner tube of U shape fitted with neon gas was. and globules of sodium. For good performance, 300% i temperature is to be maintained. ore + To protect discharge tube it is contained in evacuated double walled glass jacket. This prevents heat loss + At starting, electric discharge is to be established 7 eectese through neon gas tll sodium gas vapourized, so at start for 10-15 min. discharge through lamp will be pink and then as sodium vaporizes, it will turn to yellow. * For this voltage of about 410 is required white normal voltage is about 165, Supply is given through a leak transformer which has high leakage reactance. ae * AS soon as discharge through the tube starts, heavy voltage drop takes place in the transformer so that —— required operating voltage is automatically impressed fig. 2-42; Sodium Vapour Lamp across the cathodes. a * PF. of these lamps is 0.3 lagging and therefore condenser can be used for PF. connection. Precaution : Care should be taken in handling these lamps, for example, if inner tube is broken and sodium comes in contact with moisture, fire will result. ‘4. Life : Normal average life of sodium vapour lamps is 2500 hrs. 5. Applications : Due to yellow light its use is limited to street lighting, flood lighting of docks, quarries etc. 6. Sizes available : 45, 60, 85, 140 W. 4.4 LED Lamp) Introduction : Electroluminescence is the emission of light due to the interaction of an electric-field with a suitable solid. These solids may be panels, Light Emitting Diodes (LEDs), light emitting films. The panels employ microcrystalline powder phosphors based on the compounds like zinc sulphide, whereas in case of LEDs, compounds like “gallium phosphide" is used. Panels require high voltage to active where as LEDs require a small voltage about 2 volts D.C. and their current densities are of higher order. In this chapter our study is limited to LEDs only, LED : It was noted in 1962 that a gallium-arsenide junction biased in the forward direction was found to be an efficient emitter of radiation. Electroluminescent p-n junctions are similar to conventional silicon or germanium diodes so far as electrical characteristics are concerned. However, when biased in the forward direction, some of the energy dissipated is converted into light rather than into resistive heating and hence called as “semiconductor lamps". A single crystal material is produced in the form of a rod by slowly withdrawing a seed crystal of gallium phosphide or gallium arsenide from a saturated melt. LEDs have similar electrical characteristics as the normal rectifying diodes have. LEDs are virtually point sources of high intensity radiation life of LED device is very long (ie. upto 100,000 hours). Fig. 2.13 : LED Lamp ‘These are mechanically robust, low current consuming.a Applications : | (i) Indicating lamps. (ii) Bi-colour indicators. | (iii) Fautt-indicators. (iv) Display-boards, (W) Decorative lighting. (vi) Wrist watches. (vil) In automobile industries as electro-mechanical control. | | (vii) In instrumentation, | | | 1, These are lamps of choice for those looking for an energy efficient alternative to incandescent | lamps: they are paired for consuming a little as 1/5" of the power and lasting upto 13 times longer | than incandescent lamps. | 2. Increasing variety in shape and colour and small size of CFL have made them more versatile ang | acceptable than traditional long tube fluorescent lamp. | 3. Construction and Working : Electrode | | | Fig. 2.14 : CFL Construction * A typical CFL consists of a gas filled gas tube with two electrodes mounted in an end cap. | It contains a low pressure mix of argon gas, mercury vapour and liquid mercury and is coated on the inside with three different phosphors. ‘* They give off light when exposed to ultraviolet radiation released by mercury atoms as they are bombarded by electrons. The flow of electrons is produced by an arc between two electrodes at the end of the tube. Ballast provides the high initial voltage required to create the starting arc and then limit current to prevent the lamp from self destruction. © Ballast themseWves can be "standard" electromagnetic, “energy efficient", electromagnetic or electronic and may have power factor correction, radio interference, suppression or other features unheard of in the world of incandescent light. 4. Colour: © With development of more efficient “tri-phosphor” coatings came smaller ‘CF* with light in red, blue and green giving white light when blended together. ‘By changing relative balance of these phosphors, manufacturers can produce range of apparent colour temperature from a coo! 4100°C to a warm 2700°K. * Colour rendering index of lamp reflect how accurately colour of an object can be determined under given light source, CFL have CRI of 82 out of 100 while incandescent have 97 which is considered excellent for fluorescent sources.mh en 5, Temperature Effects on Performance : 100. 80. Percent 60: of output 40. —T 1-80 -60 -40 -20 0 20 40 60 80 = 100 Temperature (co) Fig. 2.15 : Output versus Temperature Graph (Characteristics) ‘© The ambient temperature around a ‘CFL’ can have significant effect on light output and lamp efficiency. The optimum lamp wall temperature for CFL is generally 100°F (38°C). At very low temperature (below 32°F or 0°C) lamp output can decline to one third of the rated value or less. Because of temperature below optimum, mercury vapour will condense at cold spot, reducing number of mercury atoms available to emit uv. radiations, thus light output drops. 6 Thus compact fluorescent lighting system offers potential for significant economic and environmental savings. Therefore, versatile range of different lamp-ballast configurations is available that can provide a comfortable, productive and well-illuminated space if properly used. [2.4.6 Halogen Lamp] 1. Halogen lamps are developed filament lamps and are free from drawbacks of filament lamps. 2. Principle : “Amount of radiations in visible spectrum increases as temperature of incandescent material increases upto 6000°C absolute’. - Therefore, any material will be suitable and will have high radiating efficiency which has high melting point. Carbon and tungsten are better choices for filament lamp, having melting points of 3500°C and 3400°C respectively. 3. Drawbacks for filament lamps : Carbon vaporizes very fast beyond its working temperature of 1800°C, so large electrical input is required to produce given c.p. (Candle Power). Thus efficiency is low about 3 lumens/watt. Vaporisation of carbon results into blackening of the inside of the bulb. This phenomenon is more pronounced with carbon that in tungsten employed bulbs. 4. In 1959, along with the argon gas filling, iodine was added and the drawback was eliminated, 5. The evaporated tungsten of filament on reaching the relatively low temperature near the wall of the envelope forms a compound of tungsten iodine and is represented by the chemical reaction : W+nx + WX where, W — Tungsten X + Halogen 1 + Number of atoms. Tungsten iodine which is very volatile suffers thermal diffusion in the direction of filament and on Feaching the filament at high temperature it decomposes into the tungsten and halogen as follows : Wx, > W+nXx The tungsten so released is deposited back on the filament. Iodine, 928. In this way, evaporated tungsten is restored to the filament by i therefore, works as a transport iodine regenerative cycle.7. In order that regenerative cycle should function Ends properly, it is necessary to maintain relatively high bulb wall temperatures of 250°C. For this reason, quartz is chosen as the envelope material and its size is kept very Halogen small, and quartz also facilitates high gas filling pressure, Tungsten which is capable of giving higher light output. suppor Filament 8. Iodine being corrosive in nature created problem during filling. So CH,Br was used which was easy to fill; non- High meting corrosive in nature and has less atomic weight than that glass of iodine. aluminosilicate Fig. 2.16 : Double Ended Linear Lamp 9. Advantages of halogen lamp: © Itis available in miniature size, single ended or double ended lamps. ‘+ No blackening of lamps. © Ithas higher lumen output 22-33 lumens/watt and high operating temperature. * Ithas longer life about 2000 hrs and approximately double that of filament lamp. + Ithas better colour radiation 10. Applications : These are used in public halls, factories, photofilm OHP, car lighting, large gardens, airport runways, sport halls, photo films, T.V., studios etc. 2.4.7 Ultraviolet Lamps] ‘* Ultraviolet (UV) designates a band of the electromagnetic spectrum with wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. UV radiation is present in sunlight, and contributes about 10% of the total light output of the Sun. It is also produced by electric arcs and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights. Although long- wavelength ultraviolet is not considered an ionizing radiation because its photons lack the energy to ionize atoms, it can cause chemical reactions and cause many substances to glow or fluoresce. Consequently, the chemical and biological effects of UV are greater than simple heating effects, and many practical applications of UV radiation derive from its interactions with organic molecules. Short-wave Ultraviolet Lamps © Shortwave UV lamps are made using a fluorescent lamp tube with no phosphor coating, composed of fused quartz, since ordinary glass absorbs UVC. These lamps emit ultraviolet light with two peaks in the UVC band at 253.7 nm and 185 nm due to the mercury within the lamp, as well as some visible light. From 85% to 90% of the UV produced by these lamps is at 253.7 nm, whereas only 5-10% is at 185 nm, The fused quartz tube passes the 253.7 nm radiation but blocks the 185 nm wavelength. Such tubes have two or three times the UVC power of a regular fluorescent lamp tube. These low- pressure lamps have a typical efficiency of approximately 30-40%, meaning that for every too watts of electricity consumed by the lamp, they will produce approximately 30-40 watts of total UV output They also emit bluish-white visible light, due to mercury's other spectral lines. These "germicidal" lamps are used extensively for disinfection of surfaces in laboratories and food-processing industries, and for disinfecting water supplies.uminauion ane 2.4.8 Neon Lamp) 7 face of the cathode to very 1. Principle : “Electrons are emitted from cathode by subjecting the sur : high Cjectric stress so that electrons are forcibly ejected from orbits of atoms against nuclear centripetal force". 2. Construction and Working : It has two closely spaced electrodes sealed within a soft glass envelope containing neon, at pressure of 8 torr (1 torr = 133.322 Pascal), (1 torr = 1 mm of Hg). Two closely Soft glass: Neon: 90s Lead A (@) Miniature Neon Lamp (b) Flicking Neon Lamp Fig. 2.17 : Miniature Size Neon Lamp A * In these, cathodes are heated for emission of electrons and so they are said to have cold cathode but requires very high voltage depending upon distance between the electrodes. * To built up electric stress i.e. to discharge neon gas starting voltage of about 1.5 to 2 times of the normal running voltage. * Electric field strength near the cathode is very high and ions under the influence of stray field will gain lot of momentum which will cause cathode sputtering or disintegration. * Ina closely spaced electrode system, where the negative glow emits light, a series resistance limits the lamp current, the discharge source having a negative flow characteristic. * Too low a current will give flickering of the discharge and a high current will give a bright stable discharge, but life will be shorter and blackening of the envelope will occur. Lamp current is therefore specified to identify a standard or high brightness lamp being less than 1 mA or upto about 2.5 mA respectively. * If AC. voltage is applied, each electrode will turn +ve and -ve alternatively continuous glow is achieved © Thus such cold cathode lamps are suitable for high operating voltage and low current. Advantages : * Ithas instant glow. * Available in miniature configuration. Applications : * Its used as indicator source as unit cost is low. * Display applications, letters, numericals. * Simulation of candle flame in flickering lamp. * _ Red light for hazardous warning beacons on tall structures. 2.4.9 Neon Sign Tubes, Construction : ‘* In the form of tube even upto 9 m length and can be bend in manufacturing process to any shape/shapes.— ee —— It is a glass tubing consisting of two electrodes normally cylindrical in shape of iron, steel or copper, . jns neon. Diferene colours are obtained by varying the composition of glass and adding different substances to neon gas different colours such as orange yellow, red, green etc. are obtained. Diameters of tubing - 10, 15, 20, 30mm Carrying currents 25, 35, 60, 150 mAmp. respectively. Operating voltage - 300 to 1000 volts/m of tube length. Starting voltage ~ 1.5 times the applied voltage. ti Voltage source - Step-up transformer of high reactance to get drooping characteristic. Operating voltage - 6000 volts. Supporting structure - Mounted on wooden frame or on metallic base. Matched with step-up transformer by connecting suitable tappings for the rated current. Connections between letters - Made by nickel wires and glass tubings being slipped over them. Power factor - Very low, but improved by condensers to be connected on low voltage side of transformer. Flickering Drawbacks in Neon Sign Tubes and their Rectification : Table 2.4 I Its rectification 1. Canbe rectified by adjustment of tap- changer. 2. Remove tube, refilling by manufacturer. Drawback due to 1. Transformer secondary voltage is too low. 2. Reduction in gas pressure in tube (due to absorption of gas in electrodes). Neon Tube Circuit Precautions to be taken : 1. If installed in open - frequent cleaning is required, say 4 times in a year. 2. Keep the key of open lock system with operator while work is being done for safety. Applications of Neon Sign Tubes : 1. Advertising. 2. For signs. 3. Decorative treatment of buildings. glass tubing High vol ‘metal-sheathed cable Low voltage cable ~ Transformer marked: Danger High voltage Capacitor for PF Correction with high resistance leak Fireman's Locked Switch main switch Fig. 2.18 : Neon tube circuit with accessories2.4.10 Metal Halide Lamp] y This lamp is known as mercury halide or metal halide lamp. It has a short arc tube. Inside it there are series of lamps combined within a single arc tube with output characteristics of different mixtures of elements. When such metals (like thallium, indium, sodium, dysprosium) are introduced into mercury arc tube, the mercury spectrum is suppressed reducing the ultraviolet radiation but added metal atoms partly compensate by causing a wide range of spectral bands to be emitted. It is possible to produce white or green light. If the metals are used in the element form they attack the discharge tube. To avoid this instead of metals in element form its halide is used like iodide ie. sodium iodide. The lamps require high starting voltage. This is provided by ignitor as shown connector in Fig. 2.18. Ignitor is connected across the lamp ternal, This type of starter (ignitor) enables the lamp to be restruck within a minute of being switched of (a) Metal Halide Lamp (b) Control Circuit with Ignitor for a Metal Hal Fig. 2.19 Uses: 1. Used for high bay interior and high mast exterior installations. 2. Sports stadium where coloured T.V. transmission is expected. 3. Flood lighting projectors. 41_ LASER) Long form of LASER is Light Amplification by Simulated Emission of Radiation. When external energy is applied on an atom, electron jumps from lower energy level to higher energy level state. * Itemits electromagnetic radiations and light. * Its colour depends on frequency and wavelength. © Phonon energy is released. . Afterwards electron goes to its previous lower energy level emitting photon in the process. The laser beam intensity depends on size of laser rod, optical cavity, location reflectivity of mirrors. Types of Lasers : () Liquid lasers, (i) Gas lasers, (i) Chemical lasers, (iv) X-ray lasers, (v) Semiconductor lasers, (vi) Optically pumped solid state lasers. Advantages : (i) Laser travels very long distances. (ii) Laser can be used for beautification. (ii) Used in medical equipments. (iv) Useful in metal processing industries.Disadvantages : (i) Much costly. (un Can damage to organs. (wv) Other equipments like operating equipments and control gears are needed. Applications: (For special ight effects in media-work. (ii) Safety precautions needed. (ii)_In medical field - for surgeries. ibid, [ft lL [iid oll ig. lL la i iy it i te ga |? petite i. [WED lis | HULA an A | 8] _ e 3 ft fitt Ble i 2 8 3 £ g 3 i al : 3] ip? |e q hit T W@W iti |e [pt as Hel, fe |: Wt iad |ss lHepipl, |: i ~ 8 i lin Uy Hoe |, ls i Ht i eral lund [ii road ill i 1 liv 2 lil in lg li hit ilk Beit Baki Moderate | Moderate | High May H |: 3 i lle § js i 5 hi z 3. iL Nis |alsdatl, az |e ¢ z [2.5 SELECTION CRITERIA OF DIFFERENT LAMPS Mlumination Areas oe Suitable Lamp Selection 1. General house illumination. 1 @ Incandescent lamps. (ii) Fluorescent lamps. i) Compact Fluorescent Lamps (CFLs) (iv)_LeED Contd. ...2._Cinema projectors. 2,_Arclamp. 3._ Search light. 3. Ae aes il f building. 4. lalogen a 5 - eon ae eae 5. Mercury vapour lamps, Halogen lamps, Sodium oes . vapour lamps. 6._Car parks. 6._Halogen lamps. 7._Halogen lamps. 5 sore rae 8. Fluorescent tubes, Sodium vapour lamps, Mercury aan vapour lamps, LED. 9._ Rail yards/Storage yards. 9._ Sodium vapour lamps, HPMV lamps. 10. Industrial lighting. 10. HPMV lamps, Mercury iodide lamps. 11. Medial instrument 11. LASER —— 12. Shopping centre commercial places. 12. HPMV lamps, Green lighting, Fluorescent tubes, LED 13, Spots/Stadiums. 13, Metal halide lamps. 14. Indicator, night lamp. 14. Neon lamps. 15. Metal processing industry. 15. LASER 16. Neon tubes 16. Advertising 17. Decorative treatment of buildings. 17. Neon tubes, LED. 18. Halogen lamps, Metal halide lamps. 18. Flood lighting. Thus, different lamps are selected for different purposes of illuminating the areas. Dre «1. State the advantages of electrically produced light. 2. What are ranges of wavelength of (i) visible light, (ji) ultraviolet light, (il) infra red light. 3. Define radiant efficiency. 4. List the different types of lamps. 5. ®Draw constructional view of incandescent lamp and explain its working, Give its advantages. 6. Explain the working of carbon arc lamp and state its uses. 7. Draw a sketch and explain working of fluorescent lamp. What is the function of choke and starter it? 8 Compare fluorescent tube with tungsten lamp. 9. What faults can develop in fluorescent tube? What are their reasons and what actions can be tal for repairs ? 10. Explain with construction, the working of HPMV lamp. LL Write a note on mercury iodide lamp. j 12. Compare mercury iodide lamp with HPMV lamp.- fn | 13, State the uses of HPMY lamp and mercury iodide lamp. 14. Explain the working of sodium vapour lamp. 15. Write a note on Neon lamp. + 16. Explain with diagram ‘neon sign tube. Show its circuit arrangement. 17. Explain the working of halogen lamp. State its advantages and applications. \Blumination 18. Explain the working of CFL 19, Write a note on metal halide lamp and LED. 20. Give the range of illumination efficiency in lumens/watt of the following lamps: (Incandescent lamp (ii) Fluorescent lamp Gi CFL (iv) HPMV lamp, ()_ Sodium vapour lamp (vi) Halogen lamp 21, Compare the following lamps on the points of (a) Life, (b) Colour of light : (Incandescent lamp Gi) Fluorescent lamp Gi), HPMV lamp (iv) Sodium vapour lamp 22. State the effect of shadows and glare produced by lamps. Xe eae ‘Summer 2015 Explain with neat diagram, construction and working of fluorescent tube light. Refer Section 2.3. State any four differences between tungsten filament bulb and fluorescent tube light. Refer Section 2.3.2. Explain with neat sketch construction and working of high pressure mercury vapour lamp. Refer Section 2.4.1. Poked ‘Summer 2016] 1. Compare filament lamp and fluorescent lamp on the basis of following : () quality of light, (i) capital and running cost, (ii) lamp efficiency, (iv) life of lamp, (¥) voltage regulation, (vi) lumen output. Ans. Refer Section 2. Draw and explain construction of mercury vapour lamp. Ans. Refer Section 24.1. Winter 2016) 1. Explain with neat sketch the working of carbon-arc lamp with its applications. Ans. Refer Section 2.2.1. 2. Compare incandescent and fluorescent lamps on the basis of : (2) Luminous efficiency, (2) Colour rendering, (3) Effect of voltage fluctuation, (4) Life of lamp, (5) Cost, (6) Quality of light. Ans, Refer Section 2.3.2. n