CHAPTER 6 Illumination.pdf

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06/12/2012

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By Dr. KokBoon Ching

2012@J EK/FKEE1

OutlinesOutlines

y Introduction

y Important Definitions in

Lighting

y Laws of Illumination

y

Types of lamps and theircharacteristics

y Electrical Lighting Design

Lighting

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IntroductionIntroductiony Light is just one portion of the various

electromagnetic waves flying through space

which have both frequency and length.

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IntroductionIntroduction

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IntroductionIntroductiony Light is emitted through:

a) Incandescence: Solids and liquids emit visible

temperatures about 1000K.

b) Electric Discharge: When an electric currentis passed through a gas, the atoms andmolecules emit radiation whose spectrum ischaracteristic of the elements present.

c) Electro luminescence: Light is generated

w en e ectric current is passe t roug certainsolids such as semiconductor or phosphormaterials.

d) Photoluminescence: Radiation at onewavelength is absorbed, usually by a solid, andre-emitted at a different wavelength.

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IntroductionIntroduction

y Energy consumption via lighting systems is

si nificant.

y The global electricity consumption for lighting

in 2005 is estimated at 3418 TWh

(terawatthours), i.e. 19% of total global

electricity consumption.

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IntroductionIntroductiony Today the global light

production (in lumen) can

e v e as o ows on t e

different sectors:

◦ 44 % for lighting of

commercial and public

building,

◦ 29 % for industrial lighting,

◦

or res ent a g t ng,◦ 12 % outdoor lighting

(streets, security, road signs

and car parks).

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IntroductionIntroductionEnergy consumption in different sectors:

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Important Definitions in LightingImportant Definitions in Lighting

2 objectives of lighting designer:

1. to provide the right quantity of light.

2. to provide the right quality of light.

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y Luminous flux, F (lumen, lm)¾Total amount of visible li ht ower emitted b a li ht

source.

¾1 lumen = the photometric equivalent of the watt.

¾1 lumen = luminous flux per m2 of a sphere with 1 mradius and a 1 candela isotropic light source at the

centre

wa umens a nm wave eng

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Important Definitions in LightingImportant Definitions in Lightingy Illuminance, I (Lux, lx)¾The amount of li ht arrivin on a workin lane.

¾1lux = 1lm/m2. This value is used in light calculations

and design plans.

¾Or unit in foot-candles (1 Lux = 0.0929 fc) – USA.

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For example, 1000

,

into an area of one square

meter, lights up that

square meter with anilluminance of 1000 lux.

The same 1000 lumens,

square meters, produce a

dimmer illuminance of

only 100 lux.

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Important Definitions in LightingImportant Definitions in Lightingy Luminous intensity, P

candela cd = lm/sr

Measure of the luminous flux emitted by a light source

in a particular direction, measured in lumens per

steradian.

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Important Definitions in LightingImportant Definitions in Lightingy Luminance (cd/m2)

of luminous intensity in

a given direction. It

describes the amount

of light that passes

t roug or s em ttefrom a particular area,

and falls within a given

solid angle.15


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y Uniformity

spreads over an area. Non-uniform illuminance creates bright

and dark spots, which can distract and discomfort some

occupants.

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y Glare

are s a sensat on cause y re at ve y r g t o ects n an

occupant’s field of view. The key word is relative, because

glare is most probable when bright objects are located in

front of dark environments.

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Important Definitions in LightingImportant Definitions in Lightingy Colour Rendering

The colour rendering of a light source is an indicator for its

ability of realistically reproducing the colour of an object.

Colour rendering is given as an index between 0 and 100,

where lower values indicate poor colour rendering and

higher ones good colour rendering. Other index used is 1A

(extremely good), 1B (Very good), 2 (Moderate), 3 (Low),

and 4 (Little or almost none).

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y ColourTemperature (K)¾Color a earance of a lam and the li ht it

produces.

¾It’s expressed in degrees Kelvin (K).

¾Below 3300K, the source is considered as “warmlight”. Above 5300K, the source is considered as

“cold light”.

“ ”ncan escen amps: rue va ue co or empera ure.

¾Fluorescent and high intensity discharge (HID)

lamps: correlated color temperature.

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ColourColour Temperature in Temperature in

Degrees KelvinDegrees Kelvin

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Laws of IlluminationLaws of Illumination

y Inverse Square Law

illuminance from a point source and

distance.y Lambert’s Cosine Law

States that the illuminance fallin on an

surface varies as the cosine of the

incident angle, θ.

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Laws of Illumination –

Inverse Square Law

y The illuminance from a point source can be put

n t e orm

2)(d

P I =

23


Inverse Square Law

Example 1:

22 =

22

2

1

2

2

1

21

2211

/40/105.0

1mlmmlm

m

m I

I d

d I

=×⎟ ⎠

⎞⎜⎝

⎛ =

×⎟⎟ ⎠

⎞⎜⎜⎝

⎛ =

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Lambert’s Cosine Law

y The illuminance or the intensity of

illumination is written as:

NormalLuminous 2

1 D

F I =

D1

uxθ cos'

2

2 D

F I =

25

D2



y Example:

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Example 2:

Two lamps with 3000 lumens and 5000 lumens are placed at



A and B, respectively. The arrangement is shown as follows:

Normal

10 m 7 m

A

B

θ1

θ2

C is the midway between the lamps. Calculate the

illumination on the floor at positions C .27

CD

15 m

2.5 m

Solution:

Illumination at C,



LuxCOS BC

COS AC

77.4741.3236.1550003000

2212=+=×+×= θ θ

m AC 5.125.710 22 =+=

m BC 26.105.77 22 =+=

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5.12cos 1 =θ

26.10

7cos 2 =θ



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Types of Types of lampslamps• Incandescent lamps

• ungsten a ogen amps

• Fluorescent lamps

• High pressure sodium lamps

• Low pressure sodium lampsHID lamps

• Mercury vapour

• Metal halide

• Blended lamps

• LED lamps 29

Incandescent LampsIncandescent Lamps

• Efficiency: 70 – 90 % of

energy converted into heat.

• Bulb contains vacuum or

gas filling

• Efficacy: 12 lumen / Watt

• Color renderin index: 1A

• Color temperature: 2500 –

2700 K

• Lamp life <2000 hrs

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Tungsten Tungsten--Halogen LampsHalogen Lamps•Tungsten filament and a halogen gas filled bulb

•

and move to cooler wall of bulb

•Efficacy: 18 lumens/Watt

•Color rendering index: 1A

•Color temperature: warm

Advantag es:

• More compact

• Longer life

•Lamp l ife < 4000 hrs • More and whiter light

Disadvantages:

• Cost more

• Increased IR and UV

• Handling problems

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Fluorescent LampsFluorescent Lamps

STEP 2 The impact diverts the electron of the

mercury atom out of its orbit. When it snaps back

into lace ultra-violet radiations are roduced.PHOSPHOR

VISIBLE

LIGHT

ELECTRODE

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STEP 1 Electron emitted by

electrode at one end of fluorescent lamp

travels at high speed through the tube

until it collides with one of the electrons

of the mercury atom.

STEP 3 When the ultra-violet

radiations reach the phosphor crystal, the

impulse travels to one of the active centers in

the crystal and here an action similar to that

described in Step 2 takes place. This time,

however, visible light is produced.

ATOM OF VAPORISED MERCURY



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Compact Fluorescent LampsCompact Fluorescent Lamps•Different types (T12,

T10, T8 and T5 differin

Features:

Halo-phosphate

• Efficacy – 80 lumens/Watt (HF

in diameter and

efficiency

•Most efficient at ambient

temperature of 20-30 oC,

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

•Compact fluorescentlamps (CFL) have much

smaller luminaries

Compact fluorescent lamp (CFL)33

High Pressure Sodium (HPS) LampsHigh Pressure Sodium (HPS) Lamps

•Used in outdoor and indust rial applications

• - ,

starter, ceramic arc tube, xenon gas fil ling,

sodium, mercury

•No starting electrodes

•High efficacy: 60 – 80 lumen/Watt

• -

•Color temperature: warm

•Lamp l ife < 24,000 hrs

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Low Pressure Sodium (LPS) LampsLow Pressure Sodium (LPS) Lamps

• Commonly included in the HID family

• g es e cacy: - umen a

• Poorest quality light: colors appear

black, white or grey shades

• Limited to outdoor applications

• Color rendering index: 3

• Color temperature: yellow

• Lamp l ife < 16,000 hours

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Mercury Vapor LampsMercury Vapor Lamps

• Oldest HID lamp

•

gas and quartz envelope, third electrode, outer

phosphor coated bulb, outer glass envelope

• Long life and low in itial costs

• Very poor efficacy: 30 – 65 lumens/Watt

•

• Color temperature: intermediate

• Lamp li fe: 16000 – 24000 hours

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Metal Halide LampsMetal Halide Lamps• Works similar to tungsten halogen lamps

• Lar est choice of color, size and ratin

• Better efficacy than other HID lamps: 80 lumen/Watt

• Require high vo ltage ignition pulse but some have

third electrode for starting

• Color rendering index: 1A – 2

•

3000 – 6000 K

• Lamp life:

6000 – 20,000 hours

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Blended LampsBlended Lamps

•“Two-in-one” : 2 light sources in 1 gas filled bulb

• Quartz mercur dischar e tube

• Tungsten f ilament

• Suitable for f lame proof areas

• Fit into incandescent lamps fixtures

• Efficacy: 20 – 30 lumen/Watt

• Lamp li fe < 8000 hours

• High power factor : 0.95

• Typical rating: 160 W

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LED LampsLED Lamps• Newest type of energy efficient lamp

• Two t es:

• red-blue-green array

• phosphor-coated blue lamp

• Emit visible light in a very narrow

spectrum and can produce “white

light”

• Used in exit signs, traffic signals, andthe technology is rapidly progressing

• Significant energy savings: 82 – 93%

• Longest lamp li fe: 40,000 – 100,000

hours39

ReflectorsReflectors

• Impact how much light reaches

area and dist ribut ion pattern

• Diffuse reflectors:

•70-80% reflectance but declining in t ime

•Painted or powder coated white finish

• Specular reflectors:

• -

•Polished or mirror-like

•Not suitable for industrial open-type strip fixtures

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GearGear Ballast

• Current limitin device

• Helps voltage build-up in fluorescent lights

Igniters

• Start metal halide and sodium vapor lamps

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Comparing LampsComparing Lamps

Lumens /

Watt Color Life

Index

(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

Of fi ces , s ho ps , h os pi tal s, h om es 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, 5000

garages, car par ng, oo

lighting

Halogen lamp s 18-24 20 Excellen t Display, flood lig hting, stadium

exhibition grounds, construction

areas

2000-4000

High pressur e 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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Electrical Lighting DesignElectrical Lighting Design

Better lightingincreased

productivity

Two main• Choose correct

lighting level

ques ons or designer:• Choose quality of light (color

rendering)

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Recommended Light LevelsRecommended Light Levels

Illuminance

level (lux)Examples of Area of Activity

Gener al L i ht in fo r 20 Minimum servi ce il luminance in ex te rior c ir cu lat ing areas,

rooms and areas

used either

infrequently

and/or casual or

simple visual tasks

outdoor stor es , stockyards

50 Exterior walkways & platforms.

70 Boiler house.

100 Tr an sf or mer yar ds , f ur nac e r oo ms et c.150 Ci rculat ion areas in indust ry, s to res and stock rooms.

200 Mi ni mu m s er vi ce i ll um in an ce o n t he tas k

300 Medium bench & machine work , general process in

chemical and food industri es, casual reading and filing

General lighting for

interiors

.

450 Hangers, inspec tion , draw ing of fi ces , f ine bench and

machine assembly, colour work, critical drawing tasks.

1500 Very f ine bench and machine work, inst rument & smal l

precision mechanism assembly; electronic components,

gauging & inspection of small intricate parts (may be

partly provided by local task lighting)

Add it ional local ized

lighting for visually

exacting tasks

3000 Minutely detai led and prec ise work, e.g. Very small par ts

of instruments, watch making, engraving.

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SolutionSolution Power required for total fluorescent load

= 190 x 55 W = 10.45 kW

Annual Energy Savings

= (20 – 10.45) x 4000 = 38,200 kWh

Annual cost savings

= 38,200 x RM 0.22 = RM 8404.00

Replacement cost

= 190 x RM13.5/unit = RM2565.00

Simple payback period

= (RM 2565.00/ RM 8404.00) X 12 = 4 months

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Methods of LightingMethods of Lighting

Watts Per Square

Meter MethodRough calculations andnormally for checkinguse only. According to

the watts/m2 of area to

Lumen or LightFlux Method

Most commonly usedmethod in lighting

scheme design.

Point to PointMethod

Applicable toilluminate a point due

to one or moresources of light is

required. Normally for.

calculation.

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planeworkingon thereceived Lumens

Lumen MethodLumen Method

N = number of lamps

W = wattage of each lamp

MFUFW NOR DF

UF W N ××××=×××= η η

η = e icacy o eac amp umens wattUF = utilisation factor

DF = depreciation factor

MF = maintenance factor49

Utilisation FactorUtilisation Factor

planeworkingthereachingLumens UF =

0.25 – 0.35

0.35 – 0.45

Semi-IndirectLighting

Indirect

0.5 – 0.55

Lighting

DirectLighting

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Depreciation FactorDepreciation Factor

conditionsworkingnormalunder onIlluminati

conditionscleanideallyunder onIlluminati DF =

lamp

reflector

Dust absorb some light

Typical value:ranging from

1.2 to 1.4.

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Maintenance FactorMaintenance Factor

The ratio of illumination on a given area after a period

of time to the initial illumination on the same area.

Lighting efficiency is seriously impaired by blackened

lamps, by lamp life, and by dirt on the lamp reflecting

surfaces of the luminaire. The losses are due to the physical changes on lamps,

reflecting and transmitting surfaces, ceiling and walls.

yp ca va ue s a out . .

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Example 4Example 4A lecture hall with dimension of 12 m

and the illuminance required is 350 Lux.

Assuming a depreciation factor of 1.2 and

utilisation factor of 0.6 for the lighting

scheme design. If 36 W fluorescent lamps

umens watt were to e use ,calculate the number of fluorescent lamps

required.

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SolutionSolution

Area = 12 m x 10 m = 120 m2.

= 350 lux x 120 m2 = 42,000 lumens.

1 x 36 W Fluorescent lamp

= 75 lumens/W x 36 W = 2700 lumens.

= 42,000 x (1.2/0.6) = 84,000 lumens.

Nos of lamps = 84,000/2700 ≈ 32 lamps.

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