1. Unit - IV V A KUPPUSAMY, M.E., MISTE., Sr. Lecturer / EEE K.S.R. POLYTECHNIC COLLEGE TIRUCHENGODE – 637 215 Prepared by Illumination Unit - IV DISTRIBUTION AND UTILIZATION K.S.R. POLYTECHNIC COLLEGE TIRUCHENGODE 637 215 Electric Traction1

2. Illumination Unit - IV

3. Introduction Now a days all the activities of human beings in modern trend depends upon light. Natural light is not available throughout the day. Therefore artificial lighting scheme is necessary when day light is insufficient. In the olden days, gas mantle was used as a source of light. After some period, artificial lighting is produced electrically. This method of illumination is preferred much, due to its cleanliness, convenience, steady light output and reliability. For all the lighting applications, proper illumination should be provided. Because more lighting causes glare and less lighting causes fatigue on eyes.

4. Definition and units of terms used in Illumination. Plane angle. θ Radians Arc

5. Soild angle. Radians Area

6. Light is a form of energy which can be radiated like heat energy. Light may be defined as the radiant energy from a hot body causing visual sensation to the human eye. The wavelength of light is expressed in Angstrom unit. 1 A 0 = 10 -8 cm. The electromagnetic waves whose wavelength lies between 4000 A˚ to 7500 A˚ is known as light waves. Light:- It is defined as the total quantity of light energy radiated or emitted per second from a luminous body. It is denoted by F or φand is measured in lumens. Luminous flux:-

7. Luminous Intensity:- Candle power (CP):-

8. Lumen:- Illumination:-

9. M.S.C.P (Mean Spherical Candle Power):- M.H.S.C.P (Mean Hemispherical Candle Power):- Reduction factor:-

10. Luminance or Brightness:- Glare is the sensation experienced by human eye when some rays of light enter the eye directly from a source. Glare, which is caused by the source of light is called direct glare and indirect glare is caused by a shining object reflecting major part of the incident light. Glare:-

11. Lamp efficiency:- Space height ratio:-

12. Depreciation factor (DF):- Maintenance factor (DF):-

13. Utilisation factor or co-efficient of utilisation (UF):- In flood lighting scheme, a number of lamps are employed to illuminate a surface. In this case, some amount of light waves and also some light falls outside the edges of the surface. So waste light factor is also considered in the calculation of total lumens required. It value is about 1.2 for rectangular areas and 1.5 for irregular areas. Waste light factor:-

14. Absorption factor:-

15. Beam factor:- Reflection factor:-

16. To provide required illumination level. To have uniform distribution of light all over the working plane. To avoid glare and shadows as possible. To avoid too much of contrast. To provide light of suitable colour. Requirements of Good Lighting System:- Following are the two laws of Illumination. Inverse Square law. Lambert’s cosine law. Laws of Illumination:-

17. According to this law, the illumination of a surface is inversely proportional to the square of the distance between the point source and surface. Consider a point source of light S having an intensity of I lumens/steradian. Inverse Square law :-

20. Inverse square law is applicable only where the surface is normal to the light flux, but in practice this is always not possible Illumination for such cases is given by Lambert’s cosine law. This law states that the illumination is directly proportional to the cosine of angle between the normal and the lines of flux. Consider two small disc AB and CD as shown in fig. Disc AB is normal to the light flux which is inclined at an angle θ to the vertical. Since surface AB is normal to the light beam, Lambert’s Cosine law :-

21. Depending upon the requirement, the lighting system can be classified as. Types of Good Lighting System:- Direct LightingIndirect Lighting Semi - direct Lighting Semi - Indirect Lighting General Lighting

22. The light fallen directly over the surface to be illuminated. Here 90% of the light is directed downwards from the source. This section is usually employed in industries, residential lighting, commercial lighting. While designing such scheme all the possibilities which will cause glare on eye have to be eliminated. Thus a correct size of lamp with suitable fitting should be selected. These fittings are efficient, cheap and give hard light. Direct Lighting :-

23. The light does not fall on the objects directly. Here 90% of the light is directed upwards to the ceiling. The light falling on the ceiling will be reflected towards the working plane. The fitting used here should be cleaned properly otherwise illumination level will be reduced. This scheme is widely employed in halls, clubs, workshop and places where glare and shadows are to be eliminated. This system is most expensive as large proportion of light is lost in ceiling. Indirect Lighting :-

24. In this scheme about 60% of the light is directed downwards and 40% is projected upwards. This system reduces the chances of glare to the eye. It provides almost uniform distribution of light which increases the efficiency of the system. Semi - direct Lighting :-

25. In this scheme about 10% - 40% light falls directly from the source and 60 to 90% is projected upward which is received by the object due to diffuse reflection. The scheme is useful for indoor domestic lighting. It is free from glare and pleasing to eyes. This system will have low efficiency. Semi - indirect Lighting :-

26. This lighting scheme will produce equal light distribution in the upward and downward directions. This scheme is employed in industries to minimise accidents. These fittings give soft light with little shadows. The lamp fittings used in various lighting systems are shown in the figure. General Lighting :-

27. Factors to be considered while designing lighting scheme :-

29. Lighting should be such as to provide sufficient light without glare to the workmen. If an adequate lighting is provided, it will increases the rate of production, improve the quality the quality of the product and reduce the chances of accident. It is economical to have white walls, as the reflection from white colour is more when compared to any other colour. The lighting scheme should provide required illumination level with an equal distribution. The fittings employed must be clean and they should not produce any glare. The lamps should be mounted at sufficient height to provide even luminous intensity. In an industry for certain works high illumination is required. For such works portable light with reflector are provided on the machines. Reflectors which are commonly employed for industrial lighting are standard reflector, angle reflector and diffusing reflector. The light fittings must be cleaned periodically to have sufficient light. Filament lamps and fluorescent tubes are usually employed for factory lighting. Lighting Systems :-

30. Flood lighting means flooding of large surfaces with light from powerful projectors. It is employed to serve one or more of the following purposes. Flood Lighting :- For beautifying buildings at night such as public places, ancient buildings and monuments, religious buildings on important festive occasions, gardens etc. Beautification :- For showing commercial advertisement boards and publicity posters. Advertising :- For illuminating railway yards, sports stadiums, car parks, construction sites etc. Industrial and commercial operations :-

31. The principle of an arc lamp is that when two electrodes carrying current are separated through a small distance, an arc is struck between them. The arc lamps were used in the past for street lighting purposes but now a day these are used when extreme brightness is required. Most commonly use arc lamp is Carbon Arc Lamp. Arc lamp :-

32. This is the oldest type of lamp and is still being employed in cinema projectors and search lights. It consists of two hard carbon rods (Electrodes). The diameter of +ve electrode is double to that of – ve electrode. The –ve electrode is generally fixed and +ve electrode is placed in adjustable holder and the process is manually or automatic. The arc consists of carbon vapours surrounded by orange red zone of burning carbon and pale green flames. Carbon Arc lamp :-

33. Carbon Arc Lamp When the lamp is OFF, the two electrodes are touching each other due to spring pressure on +ve electrode. When the supply is ON a large current is flow through electrodes. The temperature of carbon electrode is increased and thus the +ve electrode is pulled away against its spring pressure through a small distance by coil and thus an arc is struck between electrodes. This arc is maintained by transfer of carbon particles from one electrode to other electrode Carbon Arc lamp :-

34. Carbon Arc Lamp These particles travel from +ve electrode to –ve electrode, thus after sometime of operation +ve electrode become hollow and –ve become pointed. That’s why +ve electrode is made double than –ve electrode. In carbon arc lamp 85 % of light is given by +ve electrode which produces high intensity light and only 10 % by –ve electrode and 5 % by air. The temperature of +ve electrode is 4000 o C and that of –ve electrode is about 2500 o C. The luminous efficiency of such lamps is about 9 lumen/watt Carbon Arc lamp :-

35. Filament or Incandescent Lamp When an electric current is passed through a fine metallic wire, it raises the temperature of wire. At low temperature only heat is produced but at higher temperature light radiations goes on increasing. As filament lamp consists of fine wire of high resistive material placed in an evacuated glass bulb. This type of lamps are operated at the temperature of 2500 ˚C. Incandescent lamp :-

36. A tungsten filament is enclosed in evacuated glass bulb but to improve its performance some chemical like argon or nitrogen gas are filled. When the lamp is connected to electric supply, current passes through the filament. Due to this the filament gets heated and its temperature increases. When its temperature rises about 3200 ˚C, the filament radiates light energy. Incandescent lamps are available in various power ratings. Incandescent lamp :-

37. Low initial cost. It operates at unity power factor. No need for additional accessories. Not affected by surrounding air temperature. Operates at normal system voltage. Instantaneous start and free from stroboscopic effect. Advantages :- Life and efficiency is low. Disadvantages :-

38. Candle power and efficiency of the filament lamp falls off with use. This is partly due to slow vaporization of the filament and partly due to black deposition formed inside the bulb. In tungsten halogen lamp, iodine is added to the argon gas filling. The evaporated tungsten of filament on reaching the wall on the envelope forms a compound of tungsten iodine. Halogen lamp :-

39. This tungsten iodine compound decomposes into tungsten and halogen. This tungsten is deposited back on the filament. In this way evaporated tungsten is restored to the blackening of the walls of the envelope. Therefore luminous efficiency is high through out the life of the lamp. As small envelope is used, gas is filled with high pressure. The life of halogen lamp is double that of conventional filament lamps. Halogen lamp :-

40. It has miniature size. Long life about 2000 hours. No blackening of lamp, hence no depreciation of lumens output. Advantages :- Suited for outdoor illumination of buildings, Sport halls, Public Hall, T.V. studios large gardens etc. Applications :-

41. Transparent enclosure and contain a gas or vapour at low pressure. At the two ends of the lamp, electrodes are provided for connecting the lamp to the mains. In these lamps the cathode filament emits electrons after getting heated due to supply of current. These electrons while accelerating collide with argon and mercury vapour atoms. The excited atoms of mercury give visible radiation. This is the basic principle of gaseous discharge lamps. The gas discharge lamps are capable of giving only one particular type of wavelength of electrical energy. It is due to the fact that the atoms are widely separated. But in case of incandescent lamps, the atoms in a solid filament are closely packed and are not capable of radiating energy of one frequency. Gaseous Discharge lamp :-

42. The luminance of the discharge lamp is dependent upon the composition of gas and the vapour pressure. In discharge lamps, cathodes emitting electrons by heat are termed as hot cathodes and where no heating is employed they are called cold cathodes. Lamps employing hot cathodes do not require high voltage while cold cathode lamps require very high voltage depending upon the distance between electrodes. Discharge lamps can be classified as: Sodium vapour lamp. Neon lamp. High pressure mercury vapour lamp. Fluorescent lamp. Gaseous Discharge lamp :-

43. Consists of an inner U – Shaped glass tube made of special glass. This tube contains a small amount of metallic sodium, neon gas and two electrodes, one anode and other cathode. The inner tube is enclosed with an evacuated outer glass tube to minimise the heat losses from the inner tube. The glass tube is used of U – shape because long discharge paths are necessary. The presence of neon gas serves to vaporise the sodium by producing sufficient heat. The cathode heating transformer is used to send a high voltage of about 480 volts at the time of starting. Sodium Vapour lamp :-

44. Sodium Vapour Lamp: -

46. It consists of hard glass tube enclosed in outer bulb of ordinary glass. The space between two bulbs are completely evacuated to prevent heat loss by convection from inner bulb. The outer bulb absorbs harmful ultra violet rays. The inner bulb contains argon gas with certain quantity of mercury. In addition with two electrodes on starting electrode having high resistance in series also provided. The main electrodes are made of tungsten wire in helical shape. The lamp has screwed cap and connected to supply with choke. A capacitor is connected across supply to improve power factor High Pressure Mercury Vapour lamp :- (H.P.M.V. Lamp)

47. When the supply is switched ON, full voltage is applied across main and starting electrodes. This voltage breaks down the gap and discharge through argon gas takes place. As the lamp warms up, mercury is vaporized, which increase the vapour pressure. This discharge takes the shape of intense arc. After 5 minutes, the lamp gives full light. It gives greenish blue colour light. this lamp is always suspended vertically, other wise inner glass tube may break due to excessive heat High Pressure Mercury Vapour lamp :- (H.P.M.V. Lamp)

49. it is a low pressure mercury vapour lamp. It consists of a glass tube 25 mm in diameter and 0.6 m, 1.2 m and 1.5 m in length. The tube contains argon gas at low pressure about 2.5 mm of mercury. At the two ends, two electrodes coated with some electron emissive material are placed. Fluorescent tube (Low Pressure Mercury Vapour lamp) :-

50. A choke is connected in series with the tube which act as a blast and provide a high voltage at starting glow in the tube. During running condition the same choke absorbs some supply voltage and remain a voltage of 110 V across the tube. A capacitor is connected to improve the power factor. Fluorescent tube (Low Pressure Mercury Vapour lamp) :- During Starting After Starting

52. Efficiency and life under normal conditions are three times of those for filament lamp. There will be no voltage fluctuations. The quality of light obtained is much superior. Advantages of Fluorescent tube High initial cost on account of choke and starter. Stroboscopic effect exists. Disadvantages of Fluorescent tube

53. Induction lamps works similarly to conventional fluorescent lamp, but without electrodes and filaments. There are two types of induction lamps. External inductor lamps. Internal inductor lamps. Induction Lamp

54. A choke is connected in series with the tube which act as a blast and provide a high voltage at starting glow in the tube. During running condition the same choke absorbs some supply voltage and remain a voltage of 110 V across the tube. A capacitor is connected to improve the power factor. Fluorescent tube (Low Pressure Mercury Vapour lamp) :- During Starting After Starting

55. It is the phenomenon which makes moving object like fan blades to appear to be stand - still. The reason for this is that the light from discharge lamps is not continuously emitted. The discharge through the lamp becomes zero, 100 times in a second when working on 50 Hz supply. Stroboscopic effect: -

56. Comparison between filament lamp and fluorescent lamp filament lamp Initial cost is low. There is no stroboscopic effect. The normal life is 1000 working hours. The lumens output is affected by the variation in voltage. For obtaining different colour of light, coloured glasses are to be used. The coloured glass reduces the efficiency. fluorescent lamp Initial cost is high. Stroboscopic effect exists. Normal working life is more than 5 times that of filament lamp. Voltage variations are absorbed by the choke and the lumens output remains nearly constant. Different colour lights can be obtained by using different types of fluorescent power and the efficiency remains the same for all colours.

57. It is a fluorescent lamp designed to replace an incandescent lamp. The lamps have a tube which is curved or folded and a compact electronic ballast in the base of the lamp. The tube is filled with organ and mercury vapour. A fluorescent coating painted on, inside the tube. The ballast produces an electric current to pass through the vapourised mixture for exciting the gas molecules. Energy Saving Lamps: - Compact Fluorescent Lamps: - (CFL Lamp)

58. Low energy consumption. Low maintenance cost. It stars instantly. It does not heat the surroundings. Excellent colour properties. Low operating cost. More life. Advantages The cost of CFL is 3 to 10 times greater than that of incandescent lamp. Disadvantages

59. A light emitting diode (LED) is essentially a PN junction opto- semiconductor that emits a monochromatic (single colour) light when operated in a forward biased direction. LED Lamp: -