lecture 02 illumination

8/12/2019 LECTURE 02 Illumination

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ILLUMINATION

Lecture # 02

Engr. Mrs. Munira Batool

MS Electrical EngineeringLecturer EED, UET Taxila

Power Distribution&Utilization


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Specular Reflection

When light falls on polished metallic surfaces

or silvered surfaces, then almost of it is

reflected back according to law of reflection

i.e; the angle of incidence is equal to the angle

of reflection. Only a small portion of incident

light is absorbed and there is always the image

of the source. Such reflection is known asSpecular Reflection.



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Diffuse Reflection

If light incident on coarse surfaces like paper,

roasted glass, painted ceiling etc, then it is

scattered or diffused in all directions, hense

no image of the sourse is formed. It is known

as diffuse reflection.

A perfect diffuser is one that scatters light

uniformly in all directions and hence appearsequally bright from all directions.



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REFLECTING FACTOR

Reflecting factor = reflected light / incident lightIt is also known as coefficient of reflection



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Globes and Reflectors

To avoid glare from electric arcs and

incandescent lamps, they are surrounded

more or less completely by diffusing shades orglobes. In addition a reflector may also be

embodied to prevent the escape of light in all

directions where it serves no useful purposes.



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Lighting Schemes

Different lighting schemes may be classified as

1. Direct Lighting

2. Indirect Lighting

3. Semi-direct lighting

4. Semi-Indirect lighting5. General diffusing systems



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Direct Lighting

In this form of lighting, the light from the source

falls directly on the object or the surface to be

illuminated

Light DistributionDownward distribution 60%



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Properties Uniform lighting is to be provided at the

working or reading plane

Lamps of suitable size have to be located andfurnished with such fittings so as to givecorrect degree and distribution of illumination

at the required place Keep the lamps and fittings clean otherwise

15 to 25 % of efficiency suffers



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LimitationsThough most efficient but can cause glare and

hard shadows



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Indirect Lighting

Light does not reach the surface directly

from the source but indirectly by diffuse

reflection

Light Distribution

Upward 80% , Downward 20%



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Properties The lamps are either placed behind a cornice

or in suspended opaque bowls Maximum light is thrown upwards on the

ceiling from which it is distributed all over the

room by diffuse reflection



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Limitations

In most cases 50 to 70 % greater light asproduced by indirect lighting is demended



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Semi-direct System

This system utilizes luminaries which send

most of the light downwards directly on the

working plane but a considerable amount

reaches the ceiling and walls also.

Light Distribution




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Semi-Indirect lighting

This system is basically a compromise

between the first two systems, the light is

partly received by diffused reflection and

partly direct from the source

Light DistributionUpward 75% , Downward 10%



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General diffusing systems

In this system, luminaries are employed which

have almost equal light distribution

downwards and upwards.

Light Distribution




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Illumination Required for Different Purposes

Purpose and Places Lm/m2

Precision work, Displays, Tasks requiring rapid

discrimination, extra fine work around needles of sewing

machines

Above 500

Fine engraving, inspection of fine details having low

contrast

200-500

Proof reading, drawing, sustained reading, fine assembling

, skilled bench work

100-200

Drawing offices, Art exhibition, usual reading 60-100

Museum, work of simple nature not involving closeattention to fine details

40-60

Waiting rooms, Auditoriums and in factories 20-40

Hospital Wards, Yards, Railway Platforms 5-10



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Space/Height Ratio

It is given by the ratio

Horizontal Distance between two lampsMounting height of lamps

It mainly depends on the nature of the polar curve of a

lamp when used along its reflector



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Design of Lighting Schemes and

Layouts

A well designed lighting scheme is one which

1. Provides adequate illumination2. Avoids glare and hard shadows

3. Provides sufficiently uniform distribution of

light all over the working plane



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Utilization Factor

It is the ratio of the lumens actually received by

a particular surface to the total lumens emitted

by a luminous source

= lumens actually received on working plane/Lumens

emitted by the light source



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It mainly depends on

Type of lighting system i.e; direct or indirect

Type of mounting height of the fittings

The colour and surface of walls and cielings

Shape and dimensions of the room



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For direct lighting

= between 0.4 and 0.6

For Indirect lighting

= between 0.1 and 0.35



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Depreciation Factor

This factor allows for the fact that effective

candle power of all lamps or luminous sources

deteriorates owing to blackening and/or

accumulation of dust or dirt on the globes andreflectors etc.

Its value

1/1.3 if lamp fittings are cleaned

1/1.5 if there is much dust



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Taking into concideration for gross lumens

Total Lumens = = E A

P

where

E = Desired illumination in lm/m2

A= area of working plane to beilluminated in m2

P = depreciation factor

= utilization factor



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Numerical Problems



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Purposes

Flooding is employed for the following purposes

For aesthetic purposes as for enhancing the

beauty of a building at night e.g flood lighting

of religious buildings, ancient monuments and

festive occasions

For advertising purposes

For industrial and commercial purposes e.g in

sports stadiums



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Floodlight projectors having suitable reflectors


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Floodlight projectors having suitable reflectors

fitted with standard 250-500 or 1000 watt gas

filled tungsten lamps, are employed.



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Installations of Floodlights

First Method

The projector is kept 15 to 30 m away from

the surface to be flood lighted and provideapproximately parallel beam having beam

spread of 25to 30.



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Second Method

when the projector can not be located

away from the building. In that case an

asymmetric reflector is used which direct

more intense light towards the top of the

building



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Total flux required for floodlighting purpose is

= EAW

p

Where

W = waste light factor



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Numerical Problem



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THANKSTime and Tide wait for No one

lecture 02 illumination

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