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ARTIFICIAL LIGHT

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Functions:– task – to provide enough light for people to carry out

activity.– movement – to provide enough light for people to move

about easily and safely.– display – to display the features of the building in a manner

suitable for its character and purpose

Oldest source :– flames from fires,candles,oil lamps.

Modern source– incandescent lamps / tungsten filament lamps– discharge lamps / fluorescent lamps.

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Properties of lamps Luminous efficacy

– Def: the ability of a lamp to convert electrical energy to light energy.

– Unit: lumens/watt (lm/W)– luminous efficacy = Luminous flux output

Electrical power input– data obtained from manufacturer

Life– life of a lamp decreases with time– data obtained from manufacturer– in large installation it is economically desirable that all the

lamps are replaced at same time on a specified maintenance schedule.

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Correlated Colour Temperature (CCT)– Def: the absolute temperature of a perfect radiator when

the colour appearance of the radiator best matches that of the light source.

– Unit : Kelvin (K)– lower values of CCT = higher red content.

Color Rendering Index (Ra)

– Def: the ability of a light source to reveal the colour appearance of surfaces.

– This ability is measured by comparing the appearance of objects under the light source with their appearance under a reference source such as daylight.

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Incandescent lamps / tungsten filament lamps– produce light by heating substances to a temperature at

which they glow and are luminous.– electric current passed through filament of metal and

produce heat and give out radiation. – filament made of tungsten coil due to high melting point and

low rate of evaporation.– tungsten coil is sealed inside a glass envelope and

surrounded by unreactive gasses such as argon and nitrogen to prevent oxidation or burning.

– e.g. a metal wire is heated by an electric current in a light bulb.

Discharge lamps / fluorescent lamps– produce light by passing an electric current through a gas or

vapour that has become ionised and able to conduct electricity.

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Incandescent lamps

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Tungsten Filament Lamps General Lighting Service Lamp (GLS)

– common light bulb – lower initial cost– simple installation– shorter life – higher labour and replacement cost – lower luminous efficacy – high electrical running costs – 5% of electrical energy is converted to visible light – most of the energy is consumed is given off as heat,

especially radiant (infrared) heat

Reflecting lamps– glass bulb is silvered either inside or outside and shaped to

form parabola to allow a directional beam of light – e.g. spot lamps (PAR), crown-silvered lamps (CSL), sealed

beam lamps

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Crown silvered lamps

Reflecting lamps

Spot lamps

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Tungsten filament lamps

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Tungsten-halogen lamp– small quality of halogen gas such as iodine or bromine– contained filament that run at higher temperature– use quartz instead of plain glass– longer life– higher efficiency– e.g. spot lamp, projector, car headlamp

Low-voltage bulb– filament is shorter, thicker, stronger– low heat output– used in shops for the display goods

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Fluorescent lamps Tubular fluorescent lamp

– common tubular fluorescent (MCF)– using mercury vapour at low pressure, larger surface area

of this type of lamp produces lighting of a relatively non-directional flat quality

– low glare– higher initial cost– longer life – lower running cost (labour and replacement cost)– higher luminous efficacy – 5x better than tungsten filament

lamp

Compact fluorescent lamp– fluorescent lamps in compact forms– can be installed in a conventional light fitting– suitable for domestic and office purposes– saving of electrical energy and money

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The table below shows how a compact fluorescent lamp that delivers the same amount of light as a tungsten filament light bulb only uses about one fifth the amount of electrical energy or money.

Energy Rating of Comparable Lamps Tungsten filament light bulbs 40W 60W 75W 100W Equivalent compact fluorescent lamps 9W 11W 15W 20W

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Discharge lamps Mercury discharge lamps

– coating the glass envelope with fluorescent powders or metallic halides

– e.g. Mercury Fluorescent Lamp (MBF), Mercury Halide Lamp (MBI)

Sodium Discharge lamps– produce yellow light– poor colour rendering – high luminous efficacy– e.g. Low-pressure sodium lamp (SOX), high-pressure

sodium Lamp (SON)– application: street lighting, warehouses

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Mercury discharge lamps Sodium discharge lamps

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Properties of Electric Lamps Used in Modern Lighting

Lamp Type Luminous Efficacy (lm/W)

Nominal Life (hours)

Colour Temperature

(K)

Typical Applications

Tungsten Filament (GLS)

12 1000 2700 Homes, Hotels and restaurants

Tungsten Halogen (T-H)

21 2000 - 4000 2800 – 3000 Area and Display Lighting

Compact fluorescent (CFL)

60 8000+ 3000 Homes, Offices and Public Buildings

Tubular Fluorescent (MCF)

80 8000+ 3000 – 6500 Offices and Shops

Mercury fluorescent (MCB)

60 8000+ 4000 Factories and Roadways

Mercury Halide MBI) 70 8000+ 42000 Factories and Shops

High-Pressure Sodium(SON)

125 8000+ 2100 Roadways and Area Lighting

Low-Pressure Sodium (SOX)

180 8000+ NA Roadways and Area Lighting

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Luminaires– Def: the light fitting that holds or contains a lamp – Functions:

absorb and redirect some of the luminous flux emitted by the lamp

positioning the lamp in space protecting the lamp containing the control gear

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Light Output Ratio – to classify luminaires

– Light Output Ratio LOR = Total light output of luminaire

Light output of its lamp (s)

– Downward Light Output Ratio DLOR = Downwards light output of luminaire

Light output of its lamp (s)

– Upward Light Output Ratio ULOR = Upwards light output of luminaire

Light output of its lamp (s)

LOR = DLOR + ULOR

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British Zone System / BZ System

Direct ratioDef: proportion of the total downward flux from the luminaires which

falls directly on the working plane.

Room IndexDef: a number which takes account of the proportions of the room.

• L = length of the room • W = width of the room • Hm = mounted height of the luminaire above the working

plane

)WL(H

LxWRI

m

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LIGHTING DESIGN Lumen Method

N = number of lamp fittings required E = illuminance level required (lux)A = area at working plane height (m2)F = initial luminous flux output of each lamp (lm)UF = Utilisation Factor. An allowance for the distribution effects of the luminaire and the room surfacesLLF = Light Loss Factor. An allowance for a reduction in light output caused by lamp deterioration and dirt.

= Lamp Maintenance Factor x Luminaire Maintenance Factor x Roof Surface Maintenance Factor

FxUFxLLF

ExAN

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S

Hm

Luminaire

Working plane

S max = max horizontal spacing between fittingsHm = mounted height of fitting above the working plane

Layout

Fluorescent tubes in diffusing luminaires S max = 1.5 x Hm

Filament lamps in direct luminaires S max = 1.0 x Hm

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LIGHTING CONTROL Timer control - on at 8.00 am, off at 5.00 pm. Daylight control – on or off according to the level of daylight

detected in a room. Occupation control – such as by sensors which detect noise or

movement in an area. Local switching – where it is possible to switch on lights only in the

part of the room which is being occupied.

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GLARE INDEX

Def: numerical measure of discomfort glare which enables glare to be assessed and acceptable limits recommended.

Glare Index is calculated from: a knowledge of the positions of the source and the viewpoint, luminances of the source and the surrounding and the size of the source.

The calculated index may be compared with the maximum index recommended for a particular environment.

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LIGHTING CRITERIA Light quantity: depends on the nature of the task and the light output

of lamp and luminaire. Natural light: may be used as a complete source of light or to

supplement artificial light sources. Colour quality: depends on the requirements of the task and the

colour rendering properties of the source. Glare: depends upon the brightness and contrast of light sources

and surfaces, and the viewing angles. Directional quality: depends on the three-dimensional effect required

and the nature of the lamp and luminaire. Energy use: depends on the electrical efficiency of the lamps and

the use of switches. Costs: depend on the initial cost of the fittings; the cost of replacing

the lamps (including labour); and the electricity consumption of the lamps.

Physical properties: include size, appearance and durability of fittings.

THE END

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