illumination basic and schemes

Illumination Basic & Scheme

Building Utility & Services

Topics1. 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

Topics10.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

IntroductionAs 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.

mechanical lamps and electrical lamps

Electrical LightingElectrical lighting has following

advantages :1. Cleanliness2. Easy to control3. Economical4. Easy to handle5. Steady output6. Better reliability7. Suitable for almost all purposes

etc.

Electrical Lighting

Sensitivity of Human EyeAs 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.

Terms used in Illumination1. Light

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

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

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.

Luminous Flux

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.

Plane AngleThe 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

Solid AngleThe 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

Solid Angle

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 = area of surface/ square of radius = A/ r2 steradians

Steradian

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

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

Luminous Intensity

Reduction Factor 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/ MHCPMEAN SPHERICAL CANDLE-POWER

• Mean Spherical Candle Power, a unit of measure that represents the average output of a light source measured in all directions (360°)

MEAN HORIZONTAL CANDLE-POWERThe average value of the candle-power of a light source in all directions in a horizontal plane through the source,

IlluminationWhen 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

LuxOne meter candle or lux is

defined as the illumination produced by a uniform source of one CP on the inner surface of a sphere of radius one meter.

GlareIn 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 EfficiencyIt 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 efficiencyThe efficiency of fluorescent lamp is more than tungsten lamp.

Reflection Factor

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

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

Inverse Square LawIt states that the illumination of a surface is inversely proportional to the square of the distance of the surface from the source. E α I/d2

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= I Cos α d 2

Electrical method of producing Light

Following are the methods of producing light :

1. By developing arc between two electrodes

2. By passing a current through a filament

3. By electric discharge through vapors or gases

Arc LampThe 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 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 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

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

ARC LampsFor maintaining the arc, a minimum voltage required is given by : V = (39 + 28 L ), where L is length of arc in centimeter.

Filament or Incandescent LampWorking 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.

Incandescent Lamp

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 .

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.

Properties of Metal for Filament1. 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

Sodium Vapor LampThis 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 LampWorking 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

Mercury Vapor LampOn 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 LampConstruction : 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 LampWorking 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.

Mercury Vapor Lamp

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.

Fluorescent TubeThe 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

Fluorescent TubeWorking : 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.

Advantages of Fluorescent Tube

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

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

Neon LampThese 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

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

Neon LampApplications :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

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

Halogen LampWhen 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

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

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)

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.

Advantage of CFL1. 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 CFLThe 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.

Measurement of Candle Power

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.

PhotometerPhotometers 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.

Photometer

Lighting SchemesLighting 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 LightingAs 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.

Direct Lighting

Indirect LightingIn 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.

Indirect Lighting

Semi direct LightingThis 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.

Semi indirect Lighting

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

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

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 LevelThis 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 LevelType 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 LightThis 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

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.

Utilization factor = lumens reaching at the working place

total lumens emitted by the source

Usually it varies from 0.5 to 0.8.

Depreciation FactorThe 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 facto.

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.

References

Building Services: S.M. Patil Internet Websites

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illumination basic and schemes

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