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Illumination Engineering
J. Gregorio
I. L IGHT & L IGHTING F UNDAMENTALS
Light is ”the part of the electromagnetic spectrum
sandwhiched between ultraviolet (U.V.) & infrared
(I.R.). The visible portion of this spectrum has a wavelength between 380 nm to 780 nm. Formally, light
B. Infrared Radiation
Infrared radiation has wavelengths slightly longer than
that of visible light. the C.I.E. has also divided the I.R.
region into three sections:
IR-A (780nm-1400nm)
IR-B (1400nm-3000nm)
IR-C (3000nm-106 nm)
C. Types of Lighting
Fig. 1. The visible light spectrum
There are four major types of lighting used in Illumination Engineering:
• Direct Lighting
• Indirect Lighting
• Indirect/Direct Lighting
• Mellow Lighting
1) Direct Lighting: In direct lighting, light falls from
luminaires on the ceiling directly onto the workplace.
It is highly directional & glare suppression should be
considered under flat angles. The ceiling under this
conditions may appear dark, this is called the ”cave
effect”.
is defined by the Illuminating Engineering Society of
North America (I.E.S.N.A.) as ”a radiant energy that
is capable of existing in the retina & producing a
visual sensation”. This statement implies that light, is
not only a form of energy nor that it is only a visual
sensation, but is a combination of both.
A. Ultraviolet Radiation
U.V. has wavelength shorter than that of visible radiation. The Commission Internationale de l’Eclairage
(C.I.E.) divides U.V. radiation into three categories:
UV-A (400nm-315nm) The most common type of
U.V. radiation. Sometimes overlaps with the
shortest wavelengths in the visible portion of
the light spectrum.
UV-B (315nm-280nm) What is effectively the most
damaging U.V. radiation from the sun, as it can
penetrate the atmosphere & injure biological
tissue.
UV-C (280nm-100nm) Even more damaging than
UV-B, it comes from the sun but is blocked
by the ozone layer.
Fig. 2. Direct Lighting
2) Indirect Lighting: In indirect lighting, the light
is directed at the ceiling and the walls instead of the
workplace, allowing the reflected light from these areas
to illuminate the workplace instead. This creates a diffuse
effect on the workplace and makes the ceiling seem to
increase in height. The light in these areas would be
glare-free and there is a certain flexibility in where the
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workstations here can be arranged. This does come at
the cost of energy efficiency, however.
Fig. 3. Indirect Lighting
3) Indirect/Direct Lighting: A combination of the
two previous lighting schemes, it boasts pleasant room
visuals & high user acceptance. It also a lot more flexible
when layouting the workplace thanks to the indirect
lighting share of the area of about > 60%. It gives
us a good combination of energy efficiency & lighting
quality.
Fig. 4. Indirect/Direct Lighting
4) Mellow Light: Direct & Indirect lighting combined
in a single ceiling mounted luminaire. The use of these
allow for a free workspace layout without glare & while
still maintaining energy efficiency & lighting quality.
D. Basic Concepts in Optics
When light encounters a surface, it can either be
reflected or refracted. There are three types of reflection
a ”ray” of light experiences when it hits a surface:
Specular
where light is reflected away from the surface
at the same angle as the incoming light’s angle.
Spread
where light, when hitting an uneven surface,
reflects at more than one angle (but with
eachangle being the same as the incident angle)
Diffuse
a.k.a. Lambertian scattering. In this case, light
reflects in many angles.
Refraction, on the other hand, is the effect of a material
on the velocity & direction of the light as it passes
through the material. It is dependent on two major
factors: the angle of incidence (q), & the material’s
refractive index (n). ”n” is computed by dividing the
speed of light in a vacuum by the speed of light in the
material.
3 ∗ 108
n=
v
For all practical purposes, do note that since air has a
negligible effect on the speed of light travelling through
it, we will be assuming that it’s index of refraction (n)
is 1. Snell’s law is defined by the equation:
n1 sinθ1 = n2 sinθ2
A table of the index of refraction of common materials
follows below:
Fig. 5. Table of Index of Refraction Values for Common Materials
Due to the different wavelengths comprising white
light, a phoenomenon called dispersion occurs when it
passes through a material. Shorter wavelengths of light
bend more than the longer ones.
Another phoenomenon light experiences is transmission. Transmission describes the effect of the material
which light passes through to the ray of light itself.
Absorbption, on the other hand, is where all the colours
of light save for some select wavelengths are absorbed
(and usually turned into heat).
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3) Illuminance (E): The Illuminance is a quantity
which describes the amount of light which falls on a
surface. It is measured in lux (lx). Illuminance can be
computed using the formula:
E(lx) =
Fig. 6. Light passing through a material
luminousf lux(lm)
area(m2 )
Illuminance is affected by the inverse square law, which
states that the luminous flux falling on a surface is
indirectly proportional to the square of it’s distance from
the light source.
4) Luminance (L): Luminance is the lighting parameter which describes the brightness of the surface as
cd
perceieved by the eye. It is measured in m
2 . Luminance
is mainly affected by the reflectance of the object the
light falls on.
E. Basic Parameters used in Lighting
There are four basic parameters used in describing
lighting:
•
•
•
•
Luminous Flux (φ)
Luminous Intensity (I)
Illuminance (E)
Luminance (I)
1) Luminous Flux (φ): Luminous flux is the quantity
of light emitted by a light source. It is measured in
lumens (lm). An important quantity related to this is
the Luminous Efficiency, which is measured in lm
W .
The luminous efficiency is a good indicator of a lamp’s
economic efficiency.
2) Luminous Intensity (I): The Luminous Intensity
describes the quantity of light radiated in a particular
direction. It is measured in candelas (cd). It is of particular use when talking about directed lighting fixtures &
can be described by the use of the Luminous Intensity
Distribution Curve (L.D.C.).
Fig. 8. The different light Paramters
II. S OURCES OF A RTIFICIAL L IGHT
Fig. 7. A Luminous Intensity Distribution Curve
Electric light sources are probably the most commonly
used piece of electrical equipment. It serves to convert
electrical energy to light energy. Residential, Commercial, Industrial, & Institutional facilities all require different lights to accommodate their needs. In selecting a
light source, the following should be considered:
• Installation Requirements
• Life-Cycle Cost
• Colour Qualities
• Dimming Capability
• Other Required Effects
Some commonly used types of lamps include:
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Incandescent Lamps
which produce light by passing an electric
current through a filament, heating it up to
incandescence.
Electric Discharge Lamps
which pass an electric current through a vapor/gas, intiating discharge to flouresce. Some
electric discharge lamps include:
• Low Intensity Discharge (s.a. Fluorescent
Lamps)
• High Intensity Discharge
– Mercury Vapor
– Metal Halide
– High Pressure Sodium
– Low Pressure Sodium
A. Colour Characteristics of Artificial Light Sources
White light is comprised of a mixture of wavelengths
which we percieve as colour. The combination of such
wavelengths determine whether we percieve an environment as warm or cool, and determines how well
people and furnishing inside a room look. Some important quantities to consider when talking about colour
characteristics are:
• Colour & Efficiency
• Colour Rendering
• Colour Rendering Index (C.R.I.)
• Colour Temperature (Chromacity)
III. L IGHT S OURCES
In Pre-heat operation, the fluorescent lamp’s electrodes
are heated prior to initiating the discharge. A starter
switch closes and allows current to flow between the
electrodes, heating them up. Once the electrodes are
heated, the switch is then allowed to cool down, opening
it and simultaneously triggering the supply voltage to
initiate the discharge. No auxillary power is applied
across the electrodes during the operation. In Rapid
Start operation, on the other hand, the lamp’s electrodes
are heated before & during operation. The ballast
xformer also has two special secondary windings to
supply the proper low-voltage values to the electrodes.
Finally, Instant Start operation lamps forgo the preheating process and instead, have the ballast provide a
high (when compared to pre-heat & rapid start lamps)
starting voltage.
In general, we can describe a fluorescent lamp as a
glass tube containing argon, krypton & a small amount
f mercury gas. This glass tube has an internal coating
of phosphor as well. The electrodes (a.k.a. cathodes) are
located on each end of the tube. When a suitable enough
voltage is applied to these terminals, an electric arc is
produced, exciting the gas inside and producing light.
This also vaporizes the mercury in the tube, making it
emit U.V. light which is then converted to visible light
when it strikes the phosphor coating inside the tube.
Statisctically, discharge lamps comprise of about 80%
of the total artificial lighting needs. 95% of these are
low pressure mercury discharge lamps. Fluorescent lamp
sizing can be computed by their ”TX” designation, where
the diameter can be computed as:
A. Low-Intensity Discharge Lamps
Commonly referred to as Fluorescent Lamps, these
gas discharge lamps produce a good quantity of light
for little enrgy cost. Fluorescent lamps have various
operating modes, which mainly depend on how the
electrodes are brought up to their operating temperature.
These modes are:
• Current controlled pre-heating in choke/starter
mode.
• Voltage controlled pre heating with additional
xformer windings in ”rapid start” mode.
• ”Cold Start” ( no pre-heating )
Thanks to the use of the ”Electronic Ballast” ( a
device which controls the starting voltage and operating
currents of a lighting device ), a high working frequency
(between 35kHz & 50kHz) is achieved from the mains
(50Hz/60Hz), thus, removing any discernable flicker
in the fluorescent lamp. Fluorescent lamps have three
designations:
• Pre-heat
• Rapid Start
• Instant Start
Diameter =
X
8”
What follows is a list of common fluorescent diameters:
TX
T12
T10
T8
T5
T2
D(in)
12/8”
10/8”
8/8”
5/8”
2/8”
D(mm)
38mm
32mm
25mm
16mm
7mm
B. Linear/Tubular Fluorescent Lamps
Linear fluorescent lamps can easily be identified according to their designation code, which is broken down
below:
F − 40 − T 12 − ∗CW − /ES − /RE7 − 35
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Lamp Type
Wattage
Diameter
Lamp Colour*
Energy Saving*
C.R.I.*
Colour Temperature*
F/L - Fluorescent, FB/FU U-Bent Lamp, FT - Twin
tube T5
40
T12
CW - Cool White, WW Warm White, etc
ES - Energy Saving, HO High Output, VHO - Very
Hugh Output
RE7 (rare earth phosphors)
achieves a CRI of 70.
3500 K
Therefore, for a lamp designated as L18W/930, we
can say that this is a fluorescent lamp rated for 18W
with a CRI of 90% and a colour temperature of 3000
K. Some technical advantages of these types of lamps
include:
•
•
•
•
Lower depreciation of Luminous Flux
High Luminosity
Large selection of light colours & Optimum colour
rendering
More environmentally friendly
1) Colour Temperature: Color temperature is a metric
by which we can measure the degree of colour of a light
source. It is based on the Kelvin temperature required for
a black body to give off light of the same colour as the
sample. The table below shows the different temperature
ranges for common whites.
Color
Temperature
Light Appearance
2000K
-3000K
Warm
White
3100K
4500K
Cool
White
-
4600K 6500K
Daylight
IV. C ALCULATIONS IN I LLUMINATION E NGINEERING
(1) Luminous Flux (φ/F)
-the light energy radiated out per second from a luminous
body in the form of waves. Measured in lumens.
φ = I(∆W )
∆W is defined as ”a solid angle subtended @ the center
of a sphere.
∆W =
4πr2
A
= 2 = 4πsteradion(Sr)
2
r
r
∆φ = 4πI
(2) Luminous Intensity
-candle power of source in any direction (cd)
∆φ lumen
I=
∆W
Sr
(3) Mean Spherical Candle Power
φ lumen
M SCP =
4π
Sr
(4) Mean Hemi-Spherical Candle Power
φ lumen
M HSCP =
2π
Sr
(5) Illumination/Illuminance (E)
-is a measure of how much light falls on an area, its
units are dependent on the unit for area used.
lumen
• 1lux (lx)= 1
m2
lumen
• 1footcandle (fc) = 1 f t2
lumen
• 1 Phot (Ph) = 1 cm2
For light falling on a horizontal surface:
I
cos(θ)
d2
For light falling on a vertical surface:
E=
I
sin(θ)
d2
(6) Efficiency (Specific Output)
E=
lm
4πM SCP
=
W
W
(7) Principle of Photometry
η=
Eα
where r is also d
E=
Fig. 9. Colour Temperature Scale
I
r2
kI
r2
where k is:
• k = 1 (direct)
• k = cos(θ) (Horizontal)
• k = sin(θ) (Vertical)
• θ = angle of incidence beween Ep and the Normal
Line
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A. The Lumen Method
E=
N ∗ φ ∗ CU ∗ LLF
A
where:
• E = Illuminance
• N = No. of lamps
• φ = lamp lumens
• CU = Coefficient of Utilization
• LLF = Light Loss Factor
• A = Workplace Area