electric lighting.pptx

8/10/2019 electric lighting.pptx

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NATURE OF LIGHT

Light is a form of energy which is radiated by bodies whose

temperatures are increased. The energy transmitted by the sun is

received without heating or lighting the space in between and

without any obvious transmitting agency such as copper conductors

in case of electrical energy. The energy is released when it strikes a

solid object. The energy radiated in such a fashion is called radiant

energy .Visible light wavelength varies from 4000 to 7000 angstrom.


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ARC LAMPS: An arc lamp or arc light is a lamp that produces light by

an electric arc (also called a voltaic arc). The carbon arc light, which

consists of an arc between carbon electrodes in air, invented byHumphrey Davy in the early 1800s, was the first practical electric light.


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ELECTRIC LIGHT BULB: An incandescent light bulb, incandescent lamp

or incandescent light globe is an electric light which produces light

with a wire filament heated to a high temperature by an electric

current passing through it, until it glows.

CFL : A compact f luorescent lamp (CFL), also called compact

fluorescent light, energy-saving light, and compact fluorescent tube,

is a fluorescent lamp designed to replace an incandescent lamp.

LEDs: Light Emitting Diode (LED) lamps are used for both general and

special-purpose lighting.


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Luminanceis a photometric measure of the luminousintensity per unit area of light travelling in a given direction.It describes the amount of light that passes through or isemitted from a particular area, and falls within a given solidangle.


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Laws of illumination

1) Inverse square law

2) Lamberts cosine law


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To extend the useful hours in the day

To assist the performance of a visual task

To display or reveal something


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1)Task Lighting

2) Accent Lighting

3)General Lighting(Ambient Light)


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Task Lighting Accent Lighting

General Lighting


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FACTORY LIGHTING:Factory lighting should be such that it provides sufficient light without

glare to the workmen.


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FLOOD LIGHTING:It is employed for flooding any open large surface with light. High rating of filamentlamps or discharge lamps are used for this purpose.


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Downlighting is most common, with fixtures on or recessed in the ceilingcasting light downward

Has dramatic problems with glare and excess energy consumption due tolarge number of fittings.

The introduction of LED lighting has greatly improved this by approx.90%


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Uplighting is less common, often used to bounce indirect light off the ceilingand back down

Uplighting (indirect) uses a diffuse surface to reflect light in a space and can

minimize disabling glare

More uniform presentation of the light output in operation

Indirect lighting is completely reliant upon the reflectance value of the surface.


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Front lighting is also quite common, but tends to make the subject

look flat as its casts almost no visible shadows.

Lighting from the side is the less common, as it tends to produce glare near eye level

Backlighting either around or through an object is mainly for accent.


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LIGHTING SCHEMES

DIRECT LIGHTING:

In this scheme, light falls directly on the object to be illuminated

All the possibilities which will cause glare on eyes have to be

eliminated

Dirt if accumulated on the lamp, shade or diffuser will decrease

the luminous intensity and further it will no more remain equally

distributed.


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INDIRECT LIGHTING:

It is widely employed for illuminating drawing offices, workshops etc.

where shadows are to be eliminated, but light requirement is more than

direct lighting ( 50-100%).

The lamps are placed in opaque type shades

The maximum light is thrown towards the ceiling from where it reaches

the object by diffusion or reflection.


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SEMI-DIRECT SYSTEM:

This system is efficient and reduces the chances of glare to the eye to a

considerable extent.The shades used re of such a type that about 60%of the light s directed

downwards and 40% is projected upwards.

It provides almost a uniform distribution of lights which increases efficiency.

SEMI-INDIRECT LIGHTING:

In this system, the light received by an object is due to:

Diffused reflection

Directly thrown

GENERAL DIFFUSING SYSTEM:

In this system, shades employed will produce equal distribution upwards and

downwards.


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DESIGN OF LIGHTING SCHEMEFor designing a lighting scheme, he following factors should be

taken into consideration:

1.Space height ratio

2.Utilization factor

3.Depreciation factor


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SPACE HEIGHT RATIO

It is defined as the ratio of horizontal distance between lamps and

mounting height of the lamps.

When reflectors are used, this value is between 1 and 2.


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Utilization factor:

It is given as the ratio of total lumens utilised on working planes and the lumens

radiated by the lamp.

The value of this coefficient depends on:

Area to be illuminated

Height at which the lamps are fitted

Colour of surrounding walls, ceilings and fittings

Type of lighting direct or indirect


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Depreciation factor

When lamps are covered with dust, dirt and smoke, they do not radiate out thesame amount of flux as when they do at the time of fitting.

The depreciation factor takes into account all losses of flux.

electric lighting.pptx

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