1. Introduction
As we know that almost all human activities depends on light. Sun is a prime natural source of light but artificial lighting plays almost main role in our daily life. These artificial lights are produced by mechanical lamps and electrical lamps. But due to poor performance the mechanical light are totally replaced by electrical lights. The electrical lighting are mainly used for decorative purpose, advertising, traffic control , medical field and street lighting etc.
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2. Electrical Lighting Electrical lighting has following advantages :
Cleanliness
Easy to control
Economical
Easy to handle
Steady output
Better reliability
Suitable for almost all purposes etc.
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3. Sensitivity of Human Eye
As we know natural light consists of seven colors having different wavelengths. The average human eye is most sensitive to a wave length of A. The relative sensitivity of eye for a particular wave length is the visual effect produced by the light on the average human eye as compared with the effect of light having wave length A on human eye.
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4. Sensitivity of Human eye
This is also known as Relative luminosity Factor.
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5. Terms used in Illumination
Light
Luminous flux
Lumen
Plane angle
Solid angle
Steradian
Candle power
Glare
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6. light
That part of radiant energy from a hot body which produced the visual sensation on human eye is called light.
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7. It is represented as F of Ø and measured in lumens.
Luminous Flux
The total quantity of radiant energy per second responsible for visual sensation from a luminous body is called Luminous Flux.
It is represented as F of Ø and measured in lumens.
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8. Lumen
It is the unit of luminous flux. One lumen is defined as the luminous flux emitted per unit solid angle from a point source of one candle power.
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9. Plane Angle
The angle subtended at a point by two converging lines lying in the same plane is called plane angle. It is measured in radians and equal to the ratio of the length of the arc too its radius,
θ = arc/ radius = l/ r radians
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10. Solid Angle
The angle subtended by the partial surface area of a sphere at its centre is called as solid angle. It is measured in steradians and equal to the ratio of area of the surface to the square of radius of sphere,
ω = area of surface/ square of radius = A/ r2 steradians
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11. Steradian
the unit of solid angle. One steradian is defined as the solid angle that is subtended at the centre of a sphere by its surface having area equal to radius square,
ω = surface area/ (radius)2
= r 2 / r2 = 1 steradian
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12. Candle Power
The light radiating capacity of a source is called its candle power. The number of lumens given out by a source per unit solid angle in a given direction is called its candle power. It is denoted by C.P.
Total flux emitted = CP X solid angle
= 1 X 4π = 4π lumens
= 4π lumens
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13. Luminous Intensity
Luminous intensity in any particular direction is the luminous flux emitted by the source per unit solid angle in that direction.
It is denoted by I and its unit is candela or candle power (CP) .
Luminous intensity of source in a particular direction, I = φ / ω
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14. Illumination
When light falls on a surface, it becomes visible, the phenomenon is called as illumination. It is defined as luminous flux falling on a surface per unit area. It is denoted by E and measured in lumen per square meter or meter- candle. E = Ф / A lux
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15. Lux
One meter candle or lux is defined as the illumination produced by a uniform souce of one CP on the inner surface of a sphere of radius one meter.
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16. Glare
In the human eye, the opening of pupil is controlled by its iris which depends upon the intensity of light received by the eye. If the eye is exposed to a very bright source of light, the pupil of the eye contracts automatically in order to reduce the amount of light admitted and prevent damage to the retina. This effect is called glare. Glare is defined as the brightness within the field of vision of such a character so as to cause discomfort and interference in vision.
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17. Electrical method of producing Light
Following are the methods of producing light :
By developing arc between two electrodes
By passing a current through a filament
By electric discharge through vapors or gases
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18. Arc Lamp
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
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19. Carbon Arc Lamp
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 vapors surrounded by orange red zone of burning carbon and pale green flames.
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20. ARC Lamps
For maintaining the arc, a minimum voltage required is given by : V = ( L ), where L is length of arc in centimeter.
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21. Filament or Incandescent Lamp
Working Principle : As we know when a room heater is switched On , it gives out red light with heat at the working temperature of 750 oC and at this temperature the radiations are mostly in infra red regions. This working principle is used to develop the filament lamp.
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22. 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 oC .
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23. Filament Lamp
A tungsten filament is enclosed in evacuated glass bulb but to improve its performance some chemical like argon or nitrogen gas are filled.
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24. Sodium Vapor Lamp
This lamp consists of discharge tube made from special heat resistance glass, containing a small amount of metallic sodium, neon gas and two electrodes. Neon gas is added to start the discharge and to develop enough heat to vaporised sodium. A long tube is required to get more light. To reduce overall dimensions of the lamp, the tube is generally bent into U-shape .
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25. Sodium Vapor Lamp Working Principle :
An electric discharge lamps require a high voltage at staring and low voltage during operation. So at starting a voltage of 450 V is applied across the lamp to start the discharge. After 10 to 15 minutes, the voltage falls to 150 V because of low power factor. To improve the power factor a capacitor is connected across the supply. The color of light produce is yellowish.
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26. Sodium Vapor Lamp
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27. Fluorescent Tube
it is a low pressure mercury vapor 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.
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28. Fluorescent Tube
The colors produce by this tubes are as : Material Color Zinc silicate Green Calcium tungsten Blue Cadmium borate Pink Calcium Holo phosphate White or day light Magnesium tungsten Bluish white
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29. Fluorescent Tube
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30. Fluorescent Tube
Working : 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.
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31. Advantages of Fluorescent Tube
Voltage fluctuation has very small effect on light output.
The luminous efficiency is more as length of rod is more.
It gives light close to natural light.
Heat radiations are negligible.
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32. Disadvantages of Fluorescent Tube
Its brightness is less.
Initial cost is more
Overall maintenance cost is high.
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33. Compact fluorescent Lamp( CFL)
The compact fluorescent lamps are becoming more and more popular now a days because of their low power consumption, low running cost, longer life, attractive look, smooth light and low maintenance. These lamps are available in different sizes and designs. They have single rod, double rod, triple rod or spiral rod. These lamps are available in different power rating e.g. 5, 7, 9, 11, 18 and 24 watt 220 V
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34. Compact fluorescent Lamp( CFL)
It is basically a low pressure mercury vapor lamp having two electrodes coated with electron emissive material placed in a glass tube. The tube is coated internally with some fluorescent material in the form of powder. In the tube one drop of mercury and argon gas is filled at low pressure.
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35. Advantage of CFL Low energy consumption. Low maintenance cost
It stars instantly
It does not heat the surroundings
Excellent color properties
Low operating cost
More life
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36. Applications of CFL
The compact size, longer life, low running and maintenance cost, instant glow makes these lamps suitable for all places where uniform illumination is required.
It is used in offices, shops, hotels, hospitals, cinema halls, residential buildings etc.
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37. Cove lighting or concealed lighting
Cove lighting is a form of indirect lighting built into ledges, recesses, or valences in a ceiling or high on the walls of a room. It directs light up towards the ceiling and down adjacent walls.[1] It may be used as primary lighting, or for aesthetic accent, especially to highlight decorative ceilings. Cove lighting is valued because it hides the fixtures, and because it provides a very even, warm light.
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38. Spotlighting
Spotlighting is a method of hunting nocturnal animals using off-road vehicles that makes special use of the eyeshine revealed by many animal species. A further important aspect is that many animals (e.g. foxes and rabbits) often remain to continually stare at the light and do not appear to see the light as a threat as they normally would view a human. It is possible to carefully approach animals on foot to a short distance if the bright light is continuously maintained on the animal to greatly improve chances of successful killing.
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39. Task lighting
Task lighting refers to increasing illuminance to better accomplish a specific activity. However, the illuminance level is not the only factor governing visibility. Contrast is also important, and a poorly positioned light source may cause contrast reduction, resulting in loss of visibility. Therefore, it can be argued that the most important purpose of task lighting in the office is not increasing illuminance, but improving contrast. Because task lighting provides focused light where needed, general lighting can be reduced.
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40. Rope light
A rope light is primarily used as a decorative lighting fixture, featuring small light bulbs linked together and encased in a PVC jacket to create a string of lights. Rope lights can be used in many applications both indoors and outdoors
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41. Neon lighting
Neon lighting consists of brightly glowing, electrified glass tubes or bulbs that contain rarefied neon or other gases. Neon lights are a type of cold cathode gas-discharge light. A neon tube light is a sealed glass tube with a metal electrode at each end, filled with one of a number of gases at low pressure.
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42. Floodlighting
Floodlights are broad-beamed, high-intensity artificial lights. They are often used to illuminate outdoor playing fields while an outdoor sports event is being held during low-light conditions. More focused kinds are often used as a stage lighting instrument in live performances such as concerts and plays.
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43. Yard lighting
A yard light or garden lantern is a free standing exterior light fixture in gardens and landscaped settings. They are usually illuminated by electricity, but occasionally natural gas., usually placed near an outdoor path or driveway to provide visibility in dark areas or areas that become dark at certain times.
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44. Underwater Lighting
Underwater Lighting is a type of Lighting specially designed for use underwater. This lighting must meet the degree of protection IPX8 which means that the underwater light is dust and water resistant according to IEC Underwater lighting operates on low voltage, 30Vdc max according to standard IEC
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