Illumination Basic and Schemes Uep in eee

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Illumination Basic & Scheme

Utilization of Electrical Energ

Topics

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1. Introduction2. Nature of light3. Terms used in illumination4. Law of illumination5. Electrical methods of producing light6. Sources of light7. Arc lamps8. Filament lamps9. Gaseous discharge lamps

Topics

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10. Sodium vapor lamp11. Mercury vapor lamp12. Fluorescent tube13. Neon lamp14. Halogen lamp15. Compact fluorescent lamp16. Candle power and its measurement17. Lighting scheme18. Street light 19. Flood lighting

Introduction

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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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• Lighting energy consumption

• 20-45% in commercial buildings

• 3-10% in industrial plants

• Significant energy savings can be realized with a minimal capital investment

Background

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• Light: electromagnetic waves in space

• Light is emitted through:

a) Incandescence

b) Electric discharge

c) Electro luminescence

d) Photoluminescence

Basic Theory

Electrical Lighting

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Electrical lighting has following advantages :1. Cleanliness2. Easy to control3. Economical4. Easy to handle5. Steady output6. Better reliability7. Suitable for almost all purposes etc.

Sensitivity of Human Eye

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As we know natural light consists of seven colors having different wavelengths. The average human eye is most sensitive to a wave length of 5500 0A.

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 5500 0A on human eye.

Sensitivity of Human eye

This is also known as Relative luminosity Factor.

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Terms used in Illumination

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1. Light2. Luminous flux3. Lumen4. Plane angle5. Solid angle6. Steradian7. Candle power8. Luminous intensity reduction factor9. Glare10. Lamp efficiency

light

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That part of radiant energy from a hot body which produced the visual sensation on human eye is called light.

Luminous Flux

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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.

Lumen• 1 lumen = the photometric equivalent of the watt

• 1 lumen = luminous flux per m2 of a sphere with 1 m radius and a 1 candela isotropic light source at the centre

• 1 watt = 683 lumens at 555 nm wavelength

Lumen

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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. Lux

• metric unit of measure for illuminance on a surface: 1 lux = 1 lumen / m2

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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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

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Steradian

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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

Candle Power

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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

Luminous Intensity

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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

Luminous intensity (I)

• measured in Candela (cd)

Luminous flux (lm)

• 4 x luminous intensity

Reduction Factor

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reduction factor of a source of light is the ratio of its mean spherical candle power to its mean horizontal candle power.

Reduction factor = MSCP/ MHCP

Illumination

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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

Lux

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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.

Glare

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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.

Lamp Efficiency

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It is defined as the visible radiations emitted by it in lumens per watt.

Usually, the light sources do not radiate energy only in the visible spectrum. The radiant energy is also accompanied with infrared and ultra violet radiations.

Sun light produces majority of radiations in the visible spectrum. The tungsten lamp produces small radiations so its efficiency is very poor.

Lamp efficiency

The efficiency of fluorescent lamp is more than tungsten lamp.

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Reflection Factor

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Whole of the light incident on a reflecting surface is not reflected. Some portion of it is absorbed by the surface.

The ratio of the reflected light to the incident light is called reflection factor.

Law of Illumination

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The illumination on a surface depends upon the luminous intensity, distance between the source and surface and the direction of rays of light. It is governed by following laws :

1.Inverse square law2.Lambert’s cosine law

Inverse Square Law

It states that the illumination of a surface is inversely proportional to the square of the distance of the surface from the source.

E α 1/d2

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The inverse square law• Defines the relationship between illuminance from a point source and distance

E = I / d2

E1 d12 = E2 d22

E = I / d2

E1 d12 = E2 d22

E = Iluminance

I = Luminous intensity

d = distance

Lambert’s Cosine Law

This law states that the illumination on any surface is proportional to the cosine of angle between the direction of the incident flux and perpendicular to the area.

E = 1/d2 cos θ

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Electrical method of producing Light

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Following are the methods of producing light :

1.By developing arc between two electrodes2.By passing a current through a filament3.By electric discharge through vapors or

gases

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Types of Lighting SystemsTypes of Lighting Systems

• Incandescent lamps

• Tungsten Halogen Lamps

• Fluorescent lamps

• High pressure sodium lamps

• Low pressure sodium lamps

• Mercury vapour

• Metal halide

• Blended

• LED lamps

HID lamps

Arc Lamp

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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

Carbon Arc Lamp

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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.

Carbon Arc Lamp

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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

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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 oC and that of –ve electrode is about 2500 oC. The luminous efficiency of such lamps is about 9 lumen/watt.

ARC Lamps

For maintaining the arc, a minimum voltage required is given by :

V = (39 + 28 L ), where L is length of arc in centimeter.

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Filament or Incandescent Lamp

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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.

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 .

Filament or Incandescent Lamp

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• Emit radiation mainly in the visible region

• Bulb contains vacuum or gas filling

• Efficacy: 12 lumen / Watt

• Color rendering index: 1A

• Color temperature: 2500 – 2700 K

• Lamp life <2000 hrs

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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Tungsten-Halogen LampsEl ect ri cal E

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• Tungsten filament and a halogen gas filled bulb

• Tungsten atoms evaporate from the hot filament and move to cooler wall of bulb

• Efficacy: 18 lumens/Watt

• Color rendering index: 1A

• Color temperature: warm

• Lamp life < 4000 hrs

Tungsten halogen lamps

• Advantages:• More compact• Longer life• More and whiter light

• Disadvantages:• Cost more• Increased IR and UV• Handling problems

Properties of Metal for Filament

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1. High melting point : so that it can be operated at high temperature.

2. High specific resistance : so that it produces more heat.

3. Low temperature coefficient : so that filament resistance may not change at operating temperature.

4. Low vapor pressure ; so that it may not vaporize

5. High ductile : so that it may withstand mechanical vibrations

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Sodium Vapor Lamp

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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 .

Sodium Vapor Lamp

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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.

Sodium Vapor Lamp

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High Pressure Sodium (HPS) LampsEl ect ri cal E

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• Used in outdoor and industrial applications

• Consist of: ballast, high- voltage electronic starter, ceramic arc tube, xenon gas filling, sodium, mercury

• No starting electrodes

• High efficacy: 60 – 80 lumen/Watt

• Color rendering index: 1 - 2

• Color temperature: warm

• Lamp life < 24,000 hrs


Low Pressure Sodium (LPS) LampsEl ect ri cal E

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• Commonly included in the HID family

• Highest efficacy: 100 - 200 lumen/Watt

• Poorest quality light: colors appear black, white or grey shades

• Limited to outdoor applications

• Efficacy: Color rendering index: 3

• Color temperature: yellow

• Lamp life < 16,000 hours

Mercury Vapor Lamp

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On the basis of pressure inside the discharge tube, the mercury vapor lamps are classified as high pressure Mercury Vapor Lamp and low pressure Mercury Vapor Lamp. High pressure M.V. Lamps are of following types :

1.M.A. type : these are operated at 220 -250 V A.C. main and made in 250 W and 400 W.

2.M.A.T. type : these are made in 300 and 500 W and operated at 200 -250 V A.C. as well as D.C.

3.M.B. type : This is operated at 200 – 250 V A.C. and made in 80 W and 125 W.

Mercury Vapor Lamp

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Construction : 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.

Mercury Vapor Lamp

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Working Principle : 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 vapor pressure. This discharge takes the shape of intense arc. After 5 minutes, the lamp gives full light.

It gives greenish blue color light . this lamp is always suspended vertically, other

wise inner glass tube may break due to excessive heat.

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• Oldest HID lamp

• Consists of: arc tube with mercury and argon gas and quartz envelope, third electrode, outer phosphor coated bulb, outer glass envelope

• Long life and low initial costs

• Very poor efficacy: 30 – 65 lumens/Watt

• Color rendering index: 3

• Color temperature: intermediate

• Lamp life: 16000 – 24000 hours

Mercury Vapor Lamps

Mercury Vapor Lamp

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Fluorescent Tube

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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.

Fluorescent Tube

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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.


Fluorescent LampsEl ect ri cal E

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• 3 – 5 times as efficient as standard incandescent lamps and last 10 – 20 times longer

• Electricity passes through a gas or metallic vapor and causes radiation

• Fluorescent tubes are hot cathode lamps

Fluorescent Tube

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The colors produce by this tubes are as :Material ColorZinc silicate GreenCalcium tungsten BlueCadmium borate PinkCalcium Holo phosphate White or day lightMagnesium tungsten Bluish white

Fluorescent Tube

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Fluorescent Lamps

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• Different types (T12, T10, T8 and T5) differing in diameter and efficiency

• Most efficient at ambient temperature of 20-30 oC,

• Compact fluorescent lamps (CFL) have much smaller luminaries

Features:

Halo-phosphate• Efficacy – 80 lumens/Watt (HF

gear increases this by 10%)• Color Rendering Index –2-3• Color Temperature – Any• Lamp Life – 7-15,000 hours

Tri-phosphor• Efficacy – 90 lumens/Watt• Color Rendering Index –1A-1B• Color Temperature – Any• Lamp Life – 7-15,000 hours

Advantages of Fluorescent Tube

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1. Voltage fluctuation has very small effect on light output.

2. The luminous efficiency is more as length of rod is more.

3. It gives light close to natural light.4. Heat radiations are negligible.

Disadvantages of Fluorescent Tube

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1. Its brightness is less.2. Initial cost is more 3. Overall maintenance cost is high.

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Neon Lamp

These lamps are operated at a very low temperature of about 200 oC that’s why these are called cold cathode discharge lamps.

Two electrodes are housed at the two ends of the tube which contain neon gas. The electrodes are made of iron or nickel cylinder without any coating and practically they do not emit electrons. It gives red light whereas with mixture of mercury and argon it gives bluish green color. Voltage require for starting and operation is 10000 V. This high voltage is obtained from transformer.

Neon Lamp

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Working :When the supply is switched ON at primary side of

transformer, a voltage of 10000 V develops across secondary side which come across two electrodes. At this voltage a discharge occurs in neon gas.

Different colors can be obtained by changing the constituents of gases and mercury filled in the tubes.

Neon Lamp

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Neon Lamp

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Applications :Neon lamps are generally used for advertising.

Most of letters having two ends at which electrodes are placed. In letter having more than two ends , the tube path is repeated for some portion.

Halogen Lamp

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Halogen lamp is a special type of tungsten filament lamp which was developed in 1959, in this lams, a small amount of halogen vapor is added to the inert gas of the bulb. Its glass bulb is small in size and mechanically strong. It operates at high temperature of 3000 oC .

Halogen Lamp

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When the supply is given to the lamp, a filament glows and produce light. The halogen in addition to inert gas causes the evaporated tungsten to resettle back on the filament during cooling, that’s why lamp can be operated at high temperature. It provides high intensity light.

Halogen Lamp

Advantages of Halogen Lamp

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1. It is smaller in size.2. It does not need any blast.3. Good colors can be obtained.4. Excellent optical control.5. Gives same output throughout life6. It has long life

Disadvantages of Halogen Lamp

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1. During maintenance the handling of lamp is difficult.

2. Radiant heat is more which heats the surroundings.

3. Operating temperature is high which effects its life.

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

Compact fluorescent Lamp( CFL)

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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.

Advantage of CFL

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1. Low energy consumption.2. Low maintenance cost3. It stars instantly4. It does not heat the

surroundings5. Excellent color properties6. Low operating cost7. More life

Applications of CFL

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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.

Comparing lamps

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Type of Lamp

Lum / Watt Color

Rendering Index

Typical ApplicationLife

(Hours)Range

Avg.

Incandescent 8-18 14 Excellent Homes, restaurants, general lighting, emergency lighting

1000

Fluorescent Lamps 46-60 50 Good w.r.t. coating

Offices, shops, hospitals, homes

5000

Compact fluorescent lamps (CFL)

40-70 60 Very good Hotels, shops, homes, offices 8000-10000

High pressure mercury (HPMV) 44-57 50 Fair General lighting in factories, garages, car parking, flood lighting

5000

Halogen lamps 18-24 20 Excellent Display, flood lighting, stadium exhibition grounds, construction areas

2000-4000

High pressure sodium (HPSV) SON

67-121 90 Fair General lighting in factories, ware houses, street lighting

6000-12000

Low pressure sodium (LPSV) SOX

101-175

150 Poor Roadways, tunnels, canals, street lighting

6000-12000

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High Efficiency Lamps & LuminariesEl ect ri cal E

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Examples (9 – 75% savings):

• Metal halide lamps to replace mercury / sodium vapor lamps

• HPSV lamps where color rendering is not critical

• LED panel indicator lamps to replace filament lamps

• Luminaries with mirror optics instead of conventional painted ones

Energy Efficiency Opportunities Energy Efficiency Opportunities

Reduction of Lighting Feeder Voltage

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• Can save energy

• Provided drop in light output is acceptable

Per

cen

tag

e

Supply voltage percentage

1) Lamp current 2) Circuit power, 3) Lamp power, 4) Lamp output 5) lamp voltage 6) lamp efficiency

Effect of voltage variation of fluorescent tube light parameters

1

2

3

4

5

6

12

3

4

5

6

6

Energy Efficiency Opportunities Energy Efficiency Opportunities

Measurement of Candle Power

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The candle power of a source in any given direction is measured by comparing it with a standard or substandard source with the help of an optical instrument called PHOTOMETER.

Photometer

Photometers are mostly based on inverse square law of illumination and may be classified as stationary and portable photometers.

The stationary photometers are usually installed in a dark room with dead black walls and ceiling in order to eliminate error due to reflected light.

The portable photometers are direct reading instruments used to measured illumination in houses, offices , commercial and industrial places.

Lighting Schemes

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Lighting schemes are classified according to the location, requirement and purpose etc. are as under :

1. Direct lighting2. Indirect lighting3. Semi direct lighting 4. Semi indirect lighting5. General lighting

Direct Lighting

As is clear from the name, in this system almost 90 to 95 % light falls directly on the object or the surface. The light is made to fall upon the surface with the help of deep reflectors. Such type of lighting scheme is most used in industries and commercial lighting. Although this scheme is most efficient but it is liable to cause glare and shadows.

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Indirect Lighting

In this system, the light does not fall directly on the surface but more than 90 % of light is directed upwards by using diffusing reflectors. Here the ceiling acts as a source of light and this light is uniformly distributed over the surface and glare is reduced to minimum. It provides shadow less illumination which is useful for drawing offices and composing rooms. It is also used for decoration purposes in cinema halls, hotels etc.

Semi direct Lighting

This is also an efficient system of lighting and chances of glare are also reduced. Here transparent type shades are used through which about 60 % light is directed downward and 40 % is directed upward. This also provides a uniform distribution of light and is best suited for room with high ceilings.

Semi indirect Lighting

In this system about 60 to 90 % of total light is thrown upward to the ceiling for diffused reflection and the rest reaches the working plane directly. A very small amount of light is absorbed by the bowl. It is mainly used for interior decoration.

General Lighting

This system employs such type of luminaries, shades and reflectors which give equal illumination in all the directions.

Design of Indoor Light Scheme

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While designing a good lighting schemes, the following points must be kept in mind :

1. It should provide adequate illumination.2. It should provides uniformly distributed

light all over working plane.3. It should avoid glare and shadows as far as

possible.4. It should provide light of suitable colors.

Factors required for Light Scheme

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The following factors are required to be considered while designing the lighting scheme :

1. Illumination level2. Quality of light3. Co efficient of utilization4. Depreciation factor5. Space height ratio

Illumination Level

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This is the most vital factor in deciding the number and wattage of luminaries so that we are able to see and recognize the object properly. Colors of the body have the property of reflecting the light in different proportions, degree of illumination, its distance from the viewer, contrast between the object to be seen and its surroundings.

Illumination Level

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Type of work recommended illumination levelOffices 100-400 lumens/ meter squareSchools 250-400 lumens/ meter squareIndustry 1000 lumens/ meter squareShops 250-500 lumens/ meter squareHotels 80-100 lumens/ meter squareHospitals 250-3500 lumens/ meter

square

Quality of Light

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This means that the illumination should not be harmful to the viewers. It should be glare free, shadow less and contrast free. Direct glare from the source of light is most common factor. Presence of polished and glassy surface will cause indirect glare unless diffused light is used. Hard and long shadows can be avoided by using a large number of lamps and adjusting the mounting height.

Co – efficient of Utilization or

Utilization Factor

A surface to be illuminated receive light either directly from the lamps or reflected from the ceiling and walls or both. In this case, the total flux reaching the surface will never be equal to the flux emitted by the lamp, due to absorption by reflectors, ceiling and walls.

total lumens emitted by the source

Usually it varies from 0.5 to 0.8.

Depreciation Factor

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The total flux emitted by the source and its fitting may be reduced due to deposition of dust upon the surfaces. Similarly quantity of light reflected from the ceiling and walls also decreases with the passage of time. This is called as depreciation factor.

Usually it varies from 1.3 to 1.6.

Space Height RatioThe ratio of space (horizontal distance ) between the two

adjacent lamps to the vertical height of the lamps above the working plane is called space height ratio.So the distance between the lamps is not too much. An ideal scheme could be when there is large number of small size lamps are used also it increases the cost of installation. So the space height ratio is 1 to 1.5.

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Lighting Maintenance

• Light levels decrease >50% due to aging lamps and dirt on fixtures, lamps and room surfaces

• Maintenance options:

• Clean equipment

• Replace lenses

• Keep spaces bright and clean

• Re-lamping

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Thank You

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