CHAP 6: ILLUMINATION

BEV 30803
Faculty of Electrical and Electronic Engineering
Semester 2, Session 2023/2024
 CONTENT

Important Methods of Lighting

Definitions Sources of Light Street Lighting
in Lighting

Introduction Levels of Lighting Industrial Lighting

Laws of Illumination Lighting Schemes Flood Lighting

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 ▪ Light is just one portion of the various electromagnetic waves
flying through space which have both frequency and length.

Introduction

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Light Ranges

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▪ Light is emitted through:
Incandescence: Solids and liquids emit visible radiation when
they are heated to temperatures about 1000 0K (degree
Kelvin).
Electric Discharge: When an electric current is passed through
a gas, the atoms and molecules emit radiation whose spectrum
is characteristic of the elements present.
Electro luminescence: Light is generated when electric current
is passed through certain solids such as semiconductor or
phosphor materials.
Photoluminescence: Radiation at one wavelength is absorbed,
usually by a solid, and re-emitted at a different wavelength

4
▪ Energy consumption via lighting systems is significant.
▪ The global electricity consumption for lighting in 2005 is
estimated at 3418 TWh, i.e. 19 % of total global electricity
consumption.

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▪ Today the global light consumed (in
lumen) by different sectors can be
divided as:
~44 % for lighting of
commercial and public
building,
~29 % for industrial lighting,
~15 % for residential lighting,
~12 % outdoor lighting (streets,
security, road signs and car parks).

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7
 Important Definitions in Lighting

to provide the right quantity of

1 light.

2 objectives of
lighting designer
to provide the right quality of
2 light.

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 ▪ Luminous flux, F (lumen, lm)

~ Total amount of visible light power emitted by a light source.

~ 1 lumen = the photometric equivalent of the watt.
~ 1 lumen = luminous flux/𝑚2 of a sphere with 1 m radius and
a 1 candela isotropic light source at the centre
~ 1 watt = 683 lumens at 555 nm wavelength

LIGHT OUTPUT

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 ▪ Illuminance, I (Lux, lx)

~ The amount of light arriving on a working plane.

~ 1lux = 1lm/𝑚2 . This value is used in light calculations and
design plans.
~ Or unit in foot-candles (1 Lux = 0.0929 fc) – USA.

LIGHT LEVEL

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For example, 1000 lumens, concentrated into an
area of one 𝑚2 , lights up that 𝑚2 with an
illuminance of 1000 lux. The same 1000 lumens,
spread out over ten 𝑚2 , produce a dimmer
illuminance of only 100 lux.

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▪ Luminous intensity, P (candela, cd = lumen/steradian, “lm/sr”)

~ Measure of the luminous flux emitted by a light source in a

particular direction, measured in lm/sr.

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 ▪ Luminance (cd/m2)

~Measure of the density of luminous

intensity in a given direction.
It describes the amount of light that
passes through or is emitted from a
particular area, and falls within a given
solid angle.

LIGHT BRIGHTNESS

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14
▪ Uniformity

~ The uniformity of illuminance

describes how evenly light spreads over
an area. Non-uniform illuminance
creates bright and dark spots, which can
distract and discomfort some occupants.

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▪ Glare

~ Glare is a sensation caused by

relatively bright objects in 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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▪ 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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▪ Colour Temperature (0K)

~ Color appearance of a lamp and the light it produces.

~ It’s expressed in 0K.
~ Below 3300 0K, the source is considered as “warm light”.
Above 5300 0K, the source is considered as “cold light”.
~ Incandescent lamps: “true value” color temperature.
~ Fluorescent and high intensity discharge (HID) lamps: correlated color
temperature.

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Colour Temperature (0K)

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 Laws of Illumination

Inverse Square Law

Defines the relationship 1

between the illuminance from a
point source and distance.
Lambert’s Cosine Law

2 States that the illuminance

falling on any surface varies as
the cosine of the incident angle,
.

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 ▪ Inverse Square Law

~ The illuminance from a

point source can be put in the
form:
P
I=
(d ) 2

INVERSE SQUARE LAW

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 EXAMPLE 1

I1 (d1 ) 2 = I 2 (d 2 ) 2
2
 d2 
I1 =    I 2
 d1 
INVERSE SQUARE LAW 2
 1m 
I1 =   10lm / m = 40lm / m
2 2

 0.5m 

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 ▪ Lambert’s Cosine Law

~ The illuminance or the

intensity of illumination is
written as:

D1

F
Luminous Flux
Normal
I= 2

D1
LAMBERT’S COSINE LAW
D2

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EXAMPLE 1

LAMBERT’S COSINE LAW

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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 in figure below.
C is the midway between the lamps. Calculate the illumination
on the floor at positions C.
A

Normal
B

10 m 7m
θ1
θ2

LAMBERT’S COSINE LAW

D C
2.5 m

15 m

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 Solution:
Illumination at C,
3000 5000
= 2
 COS 1 + 2
 COS 2 = 15.36 + 32.41 = 47.77 Lux
AC BC

AC = 102 + 7.52 = 12.5m

BC = 7 2 + 7.52 = 10.26m

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cos1 =
12.5
LAMBERT’S COSINE LAW
7
cos  2 =
10.26

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EXERCISE 1
Two lamps with 4000 lumens and 5500 lumens are placed at A
and B, respectively. The arrangement is shown in figure below.
C is the midway between the lamps. Calculate the illumination
on the floor at positions C.
A

Normal
B

10 m 7m
θ1
θ2

LAMBERT’S COSINE LAW

D C
2.5 m

15 m

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 Types of lamps

Incandescent lamps
Mercury vapor (HID)
Tungsten Halogen Lamps
Metal halide (HID)
Fluorescent lamps Blended lamps
High pressure sodium lamps (HID) LED lamps

Low pressure sodium lamps (HID)

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Incandescent Lamps

• Efficiency: 70 – 90 % of energy
converted into heat.
• Bulb contains vacuum or gas filling
• Efficacy: 12 lumen / Watt
• Color rendering index: 1A
• Color temperature: 2500 – 2700 K
• Lamp life <2000 hrs

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 Tungsten-Halogen Lamps

• Tungsten filament and a halogen gas filled bulb

Advantages:
• More compact
• Tungsten atoms evaporate from the hot filament
• Longer life
and move to cooler wall of bulb
• More and whiter light • Efficacy: 18 lumens/Watt
Disadvantages:
• Color rendering index: 1A
• Cost more
• Increased IR and UV • Color temperature: warm
• Handling problems
• Lamp life < 4000 hrs

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 Fluorescent Lamps
VISIBLE
STEP 2 The impact diverts the LIGHT
electron of the mercury atom out of its
orbit. When it snaps back into place, ultra- PHOSPHOR
violet radiations are produced. CRYSTALS

ELECTRODE

ATOM OF VAPORISED MERCURY

STEP 1 Electron emitted by electrode at one

STEP 3 When the ultra-violet radiations reach the
phosphor crystal, the impulse travels to one of the
end of fluorescent lamp travels at high speed
active centre in the crystal and here an action similar to
through the tube until it collides with one of the
that described in Step 2 takes place. So the visible light is
electrons of the mercury atom.
produced.

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 Compact Fluorescent Lamps
Features: • Different types (T12, T10, T8 and T5)
Halo-phosphate differing in diameter and efficiency
• Efficacy – 80 lumens/Watt (HF • Most efficient at ambient
gear increases this by 10%) temperature of 20-30 0C,
• Color Rendering Index –2-3 • Compact fluorescent lamps (CFL)
• Color Temperature – Any have much smaller luminaries
• 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

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Low Pressure Sodium (LPS) Lamps

• Commonly included in the HID family

• Highest efficacy: 100 - 200 lumen/Watt
• Poorest quality light: colors appear black, white or
grey shades
• Limited to outdoor applications
• Color rendering index: 3
• Color temperature: yellow
• Lamp life < 16,000 hours

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 Comparing Lamps
Lumens /
Watt Color
Life
Type of Lamp Rendering Typical Application
(Hours)
Range
Avg. Index

Incandescent 8-18 14 Excellent Homes, restaurants, general 1000

lighting, emergency lighting

Fluorescent Lamps 46-60 50 Good w.r.t. Offices, shops, hospitals, homes 5000
coating

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 parking, flood
lighting

Halogen lamps 18-24 20 Excellent Display, flood lighting, stadium 2000-4000

exhibition grounds, construction
areas

High pressure sodium (HPSV) 67-121 90 Fair General lighting in factories, ware 6000-12000
SON houses, street lighting

Low pressure sodium (LPSV) 101- 150 Poor Roadways, tunnels, canals, street 6000-12000
SOX 175 lighting

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Mercury Vapor Lamps

• Oldest HID lamp

• Consists of: arc tube with mercury and argon gas
and quartz envelope, third electrode, outer
phosphor coated bulb, outer glass envelope
• Long life and low initial costs
• Very poor efficacy: 30 – 65 lumens/Watt
• Color rendering index: 3
• Color temperature: intermediate
• Lamp life: 16000 – 24000 hours

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Metal Halide Lamps

• Works similar to tungsten halogen lamps

• Largest choice of color, size and rating
• Better efficacy than other HID lamps: 80 lumen/Watt
• Require high voltage ignition pulse but some have
third electrode for starting
• Color rendering index: 1A – 2
• Color temperature:
3000 – 6000 0K
• Lamp life:
6000 – 20,000 hours

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Blended Lamps

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

• Quartz mercury discharge tube
• Tungsten filament
• Suitable for flame proof areas
• Fit into incandescent lamps fixtures
• Efficacy: 20 – 30 lumen/Watt
• Lamp life < 8000 hours
• High power factor: 0.95
• Typical rating: 160 W

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LED Lamps
• Newest type of energy efficient lamp
• Two types:
• 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, and the technology is
rapidly progressing
• Significant energy savings: 82 – 93%
• Longest lamp life: 40,000 – 100,000 hours

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Reflectors
• Impact how much light reaches on the surface and is
its distribution pattern
• Diffuse reflectors:
• 70-80% reflectance but declining in time
• Painted or powder coated white finish
• Specular reflectors:
• 85-96% reflectance and less decline in time
• Polished or mirror-like
• Not suitable for industrial open-type strip fixtures

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Gears

❑ Ballast
• Current limiting device
• Helps voltage build-up in
fluorescent lights

❑ Igniters
• Start metal halide and sodium
vapor lamps

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 Illuminance Examples of Area of Activity
level (lux)

General Lighting for 20 Minimum service illuminance in exterior circulating areas,

rooms and areas outdoor stores , stockyards
used either 50 Exterior walkways & platforms.
infrequently
70 Boiler house.
and/or casual or
simple visual tasks 100 Transformer yards, furnace rooms etc.
150 Circulation areas in industry, stores and stock rooms.

200 Minimum service illuminance on the task

300 Medium bench & machine work, general process in
chemical and food industries, casual reading and filing
activities.
Recommended Light Levels
General lighting for 450 Hangers, inspection, drawing offices, fine bench and
interiors machine assembly, colour work, critical drawing tasks.
1500 Very fine bench and machine work, instrument & small
precision mechanism assembly; electronic components,
gauging & inspection of small intricate parts (may be
partly provided by local task lighting)

Additional localized 3000 Minutely detailed and precise work, e.g. Very small parts
lighting for visually of instruments, watch making, engraving.
exacting tasks

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Example 3
An industrial plant has an incandescent lighting load of comprising 100 Nos. of
60 W and 140 Nos. of 100 W. Calculate the energy savings if each
incandescent load is replaced by 1 x 40 W fluorescent load. Lighting is
required for 4000 hours/year and the cost of electricity is RM 0.22/kWh.
Replacement cost is RM 13.5/unit consider ballast consumption as 15 W.
Given data:
100 W incandescent lamp = 2200 lumens
60 W incandescent lamp = 1320 lumens
40 W Fluorescent lamp = 2400 lumens

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 Solution

▪ Power required by existing incandescent lamps

= 100 x 60 + 140 x 100 = 6000 +14000 =20.0 kW.
▪ One 40 W fluorescent lamp each will be required to replace one 100 W incandescent and
two of 60 W lamps (as observed from given data).
▪  we require 140 nos. of 40 W fluorescent lamps (to replace 100 W incandescent lamps)
and 50 Nos. of 40 W fluorescent lamps (to replace 60 W incandescent lamps).
▪ Total number of Fluorescent lamps required
= 50 + 140 = 190 Nos.
▪ Power required for one of fluorescent lamp is 55 W (including conventional ballast power)

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 Solution
▪ 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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 Electrical Lighting
Design
Better lighting
increased productivity
Two main questions for designer:

? Choose correct lighting level

? Choose quality of light (color rendering)

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 Methods of Lighting

Point to Point
Watts/m2 Method Method
Lumen or Light
Rough calculations and Applicable to
Flux Method illuminate a point due
normally for checking
use only. According to Most commonly used to one or more
the watts/m2 of area to method in lighting sources of light is
be illuminated. scheme design. required. Normally for
flood lighting
calculation.

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 Lumens received on the working plane
UF
= N  W  
DF
OR
= N  W    UF  MF
Lumen
Method N = Number of lamps
W = Wattage of each lamp
 = Efficacy of each lamp (lm/watt)
UF = Utilisation Factor
DF = Depreciation Factor
MF = Maintenance Factor

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 Lumens reaching the working plane
UF =
Total lumens given out by the lamps

Semi-

Utilisation
Indirect
Lighting
0.25 – 0.35
Factor Indirect
Lighting 0.35 – 0.45
Direct
Lighting 0.5 – 0.55

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 Illumination under ideally clean conditions
DF =
Illumination under normal working conditions

reflector

Depreciation lamp

Factor Wall Typical value:

ranging from 1.2 to
1.4.

Dust absorb some light

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 ▪ 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
Maintenance blackened lamps, by lamp life, and by dirt on
the lamp reflecting surfaces of the luminaire.
Factor ▪ The losses are due to the physical changes
on lamps, reflecting and transmitting
surfaces, ceiling and walls.
▪ Typical value is about 0.8.

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Example 4
A lecture hall with dimension of 12 m long and 10 m wide is to be
illuminated 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 (75 lumens/watt) were to
be used, calculate the number of fluorescent lamps required.

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Solution
• Area
= 12 m x 10 m = 120 m2.
• Total lumens required
= 350 lux x 120 m2 = 42,000 lumens.
• 1 x 36 W Fluorescent lamp
= 75 lumens/W x 36 W = 2700 lumens.
• Gross lumens output by the lamps
= 42,000 x (1.2/0.6) = 84,000 lumens.
• No. of lamps
= 84,000/2700  32 lamps.

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