ABA 2309:
BUILDING ENVIRONMENT
SCIENCE II - LIGHTING
Jerusha NGUNGUI, Architect
COURSE OUTLINE
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01. Introduction to Lighting Principles
02. Illumination for Human Comfort
03. Daylighting
04. Artificial Lighting
05. Lighting internal and external spaces
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LIGHTING P RINCIP LES
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1.1 ILLUMINATION
▰
Process of lighting an object – a visual
scene inside or outside a building.
▰
Light sources include:
▻
The sun – natural lighting
(daylighting)
▻
Artificial sources
In artificial lighting the light source itself is under the designers (users)
control. In day lighting the source (sun and sky) is given, thus if control is
necessary, it must be in transmission and distribution. Artificial lighting is
practically independent of location, climate or even of the building fabric.
Daylighting however, strongly depends on the externally given conditions
and its control is only possible by the building itself.
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Image © Jerusha Ngungui
1.2 THE NATURE OF LIGHT
▰
What we perceive as light is a narrow
wavelength band of electromagnetic
radiation from about 380 to 780nm (1
nm = 10-9m).
▰
The energy radiation consists of energy
particles (photons) but also shows
transverse wave motion properties.
▰
The wavelength determines its colour.
Light containing all visible waves is
perceived as white. The human eye’s
sensitivity varies with the wavelength,
and is greatest around 550nm (yellow).
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1.3 TRANSMISSION OF LIGHT
▰
Occurs when light passes through an
object / material.
▰
Transparent materials transmit a large
part of light. Opaque materials block the
passage of light. Translucent materials
transmit a part of the incident light by
breaking its straight passage and
scattering it in all directions, creating
“diffuse” light.
▰
Distribution of light: reflected, absorbed
and transmitted.
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1.4 REFLECTION
▰
Specular reflection is direct reflection
in one direction only. i.e. the angle of
incidence (i) equals the angle of
reflection (r).
▻ Convex mirror, the reflected rays will
be divergent
▻ Concave mirror they will be
convergent
▰
Diffuse reflection is reflection in which
the light is scattered in various
directions e.g. from a matt surface.
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Image © Jerusha Ngungui
1.4 REFLECTION (cont.)
▰
Reflectance is the ratio of the luminous
flux reflected from a surface to the flux
incident upon the surface.
▰
It ranges between 0 (dark, dull surfaces)
and 1.0 (light, shiny surfaces)
Typical reflectances of building surfaces
White emulsion paint on plaster
0.8
White emulsion paint on concrete
0.6
Concrete: light grey
0.4
Timber
0.3
Bricks: dark colours
0.2
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1.5 COLOURED LIGHT
a) Light Spectrum
▰
The range to which the retina is
sensitive is comprised between 380
and 780 nm.
▰
Within this interval, each wavelength is
attributed to a colour.
▰
The longest wavelength (which
corresponds to the lowest frequency) is
seen by us as the color red followed by
the known colors of the rainbow:
orange, yellow, green, blue, indigo, and
violet which has the shortest
wavelength (and highest frequency).
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But our eye is not equally
sensitive to all colours/
wavelengths: it is little sensitive
to blue-violet and red, while is
highly sensitive to yellow-green
about 555 nm.
Wavelengths which we are
unable to perceive (occurring
just below the red and just above
the violet area), are the infrared
and ultraviolet rays, respectively.
Good lighting should be based,
whenever possible and
appropriate, on natural light supplemented when necessary
by artificial light.
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1.5 COLOURED LIGHT (cont.)
b) The Munsell System
▰
HUE: The quality by which we distinguish one
color from another, as a red from a yellow, a
green, a blue or a purple but further
subdividing each into 5 categories.
PRINCIPLE HUES
INTERMEDIATE HUES
R
Red
YR
Yellow-Red
Y
Yellow
GY
Green-Yellow
G
Green
BG
Blue-Green
B
Blue
PB
Purple-Blue
P
Purple
RP
Red-Purple
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1.5 COLOURED LIGHT (cont.)
b) The Munsell System (cont.)
▰
VALUE: the quality by which we distinguish a light
color from a dark one according to a scale from 0
(black) to 9 (absolute white).
▰
CHROMA: Intensity of colour or the degree of
colourfulness, distinguishing 14 classes. A low
chroma would be almost grey; the brightest colours
have chroma of 12 – 14.
▰
The Munsell notation is given in 3 facts:
▻
Hue – value/chroma e.g. 5R – 4/10 i.e. Red of hue 5
– value 4 / chroma 10
▻
VALUE (V) is directly relevant to lighting design.
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1.5 COLOURED LIGHT (cont.)
c) Colour mixing
▰
Additive colour mixing: If coloured lights
are added together they will produce
other colors.
▰
When the three primary additive – RED,
GREEN and BLUE (RGB) colours are
mixed in equal proportions they add to
produce WHITE light.
▰
Applications of additive colour mixing –
Stage lighting, display screens, colour
printing etc.
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Image © Jerusha Ngungui
1.5 COLOURED LIGHT (cont.)
c) Colour mixing (cont.)
▰
Subtractive colour mixing: This is the kind of
mixing you get if you illuminate colored filters
with white light from behind.
▰
When the three primary subtractive – CYAN,
MAGENTA and YELLOW (CMY) colours are
overlapped in equal proportions, all the light
is subtracted giving BLACK.
▰
Applications of subtractive colour mixing –
paint pigments, colour photographs, colour
printing etc.
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Image © Jerusha Ngungui
1.5 COLOURED LIGHT (cont.)
d) Light refraction
▰
Light refraction is the reverse process of color mixing.
It occurs as light passes across the boundary between
two media.
▰
The bending occurs because light travels more slowly
in a denser medium.
▰
As visible light penetrates a glass prism, it is refracted,
and separated into an array of visible colors.
Beams with a long wavelength (the red beams) are refracted less strongly than beams with a short
wavelength (the violet beams), causing the colors to fan out.
Each beam of light, with its own particular wavelength (or color), is slowed differently by the glass.
Since violet light has a shorter wavelength, it is slowed more than the longer wavelengths of red light.
Consequently, violet light is bent the most while red light is bent the least
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1.5 COLOURED LIGHT (cont.)
e) Colour temperature
▰
▰
▰
▰ Light sources are divided into three
Color temperature relates to the fact
groups depending on the colour
that when an object is heated, it will emit
temperature:
a color that is directly related to the
temperature of that object.
▻ 3,000 – 3,500 K: warm white colour
The higher the color temperature, the
▻ 4,000 – 5,000 K: neutral white colour
more 'blue' the light, and the lower the
▻ 5,500 – 7,000 K: cool white colour
color temperature the more 'red' the
light.
SI unit is Kelvin (K).
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Image © Jerusha Ngungui
Light sources with a low colour
temperature help to create a “warm”
environment, if the lighting levels are low,
i.e. those typical of home interiors or
general lighting in offices. A pleasant
lighting of the interior is obtained with
light sources having a colour temperature
not higher than 3,000 K.
If the general level of illumination exceeds
500 lux it may be preferable to use 4,000
K sources. Sources with higher colour
temperature when used with lighting
levels below 500 lux create an
atmosphere “cold” and unpleasant. High
values of colour temperature should be
associated with high levels of
illumination: that is what happens with
natural light outdoors.
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Image © Jerusha Ngungui
1.5 COLOURED LIGHT (cont.)
f) Colour rendering
▰
This is the ability of a light source to
reveal the colour appearances of
surfaces.
▰
This ability is measured by comparing
the appearance of objects under the
light source with their appearance
under reference source such as
daylight.
▰
Colour Rendering Index: is a scale from 0
to 100 percent indicating how accurate a
"given" light source is at rendering color
when compared to a "reference" light
source.
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1.6 DEFINITION OF TERMS
Photometry
▰ Photometry is the science of the
measurement of light, in terms of its
perceived brightness to the human eye.
▰ The eye has different responses as a
function of wavelength when it is
adapted to light conditions (photopic
vision) and dark conditions (scotopic
vision).
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1.6 DEFINITION OF TERMS (cont.)
Solid Angle : This is the angle subtended by the
partial surface area of a sphere at its center. It is
measured in steradians ().
One Steradian is defined as the solid angle
subtended at the centre of a sphere of radius “r”
by a surface element of area “r2”.
NB: The total surface area of a sphere of radius “r” is 4πr2 and therefore there are 4π
Steradians at the centre of the sphere (4πr2/r2=4π Steradians)
𝑇𝑜𝑡𝑎𝑙 𝑆𝑜𝑙𝑖𝑑 𝑎𝑛𝑔𝑙𝑒 𝑎𝑟𝑜𝑢𝑛𝑑 𝑎 𝑝𝑜𝑖𝑛𝑡 =
𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑎 𝑠𝑝ℎ𝑒𝑟𝑒
𝐴𝑟𝑒𝑎 𝑔𝑖𝑣𝑖𝑛𝑔 1 𝑠𝑡𝑒𝑟𝑎𝑑𝑖𝑎𝑛
=
4𝜋𝑟 2
𝑟2
=4𝜋
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1.6 DEFINITION OF TERMS (cont.)
Luminous Intensity (I) : Power of a light
source, or illuminated surface, to emit light in
a particular direction. SI Unit – candela (cd)
Luminous Flux (F) : Also known as luminous
power, it is the rate of flow of light energy. SI
Unit - lumen (lm) which is defined as the
luminous flux emitted within one steradian by
a point source of light of one candela.
𝐼=
𝐹

Where:
𝐼 = mean spherical intensity of the source (cd)
𝐹 = luminous flux emited by the source (lm)
 = solid angle containing the flux (sterad)
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1.6 DEFINITION OF TERMS (cont.)
Luminance (L) : Intensity of light emitted from
a surface per unit area in a given direction. SI
Unit is candela per square meter (cd/m2).
Illuminance (E) : Total luminous flux incident
on a surface, per unit area. SI Unit is lux (lx)
where 1 lux = 1 lm/m2
Luminous energy: Energy emitted in the form
of light (also known as quantity of light). It’s a
product of luminous flux and its duration,
measured in lumen seconds.
Typical lighting values in lux
Moonlight
0.1 lx
Street lighting
10 lx
Office lighting
300 lx
Overcast day
10,00 lx
Direct sunlight
100,000 lx
𝐸=
𝐹
𝐴
Where:
𝐸 = illuminance on a surface (lx)
𝐹 = total flux reaching a surface (lm)
A = area of the surface (m2)
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1.6 DEFINITION OF TERMS (cont.)
Summary of lighting measurements
Luminous efficacy : is a measure of how well
a light source produces visible light. It is the
ratio of luminous flux to power. Measured in
lumen per watt (lm/W).
Luminous exposure : The total density of light
allowed to fall on the photographic medium
(photographic film or image sensor) during
the process of taking a photograph. Exposure
is measured in lux seconds.
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Worked Examples
1. A small lamp emits a total luminous flux of 1257 lm in all directions.
Calculate the luminous intensity of this light source.
Solution:
We know 𝐹 = 1257 lm,  = 4 𝜋, 𝐼 = ?
Using the formula for intensity and substituting
𝐼=
𝐹

=
1257
4𝜋
Total intensity = 100 cd
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Worked Examples
2. A small source of light has a mean spherical intensity of 100 cd. One
quarter of the total flux emitted from the source falls at right angles onto a surface
measuring 3 m by 0.7 m. Calculate:
a) The total luminous flux given out by the source; and
b) The illumination produced on the surface.
Solution (a):
We know 𝐼= 100 cd,
 = 4 𝜋,
𝐹 =?
Using the formula for intensity and substituting
𝐼=
𝐹

100 =
𝐹
4𝜋
or
𝐹 = 4 𝜋 x 100 = 1256.8
Total flux = 1256.8 lm
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Worked Examples
Solution (b):
We know
𝐹= 1256.8 X 0.25 =314.2 lm,
𝐴 = 0.7 X 3 =2.1 m2,
𝐸 =?
Using the formula for illuminance and substituting
𝐸=
𝐹
𝐴
E=
314.2
2.1
= 149.6
Therefore illuminance = 150 lx
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02
I LLU MINATION F O R
HUMAN CO MF ORT
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2.1 LIGHT AND THE EYE
The eye
▰ Light enters the eye through the pupil, an
opening in the iris which varies diameter to
control the amount of light admitted.
▰ The cornea and the lens focus the light by
refraction onto the retina, which is the light
sensitive surface on the rear of the eye.
▰ The light receptors (rods and cones) of the
retina send electrical messages via the
optic nerve, to the brain for interpretation.
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2.1 LIGHT AND THE EYE (cont.)
Sensitivity of vision
▰ Cone vision:
▻
Cones are light receptors that operate
when the eye is adapted to normal levels
of light. Are sensitive to colour and detail
but not to light.
▰ Rod vision:
▻
Rods are light receptors that operate
when the eye is adapted to very low levels
of light. Are sensitive to light but not to
colour and detail.
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2.1 LIGHT AND THE EYE (cont.)
The eye (cont.)
▰ The convex lens focuses light from a
scene to produce an inverted image of the
scene to the retina.
▰ When relaxed, the lens focuses on distant
objects.
▰ To bring closer objects into focus, the
ciliary muscles increase the curvature of
the lens (accommodation).
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2.2 VISUAL PERFORMANCE & COMFORT
Visual field:
▰ Visual field is the total extent in
space that can be seen when
looking in a given direction.
▰ It refers to the total area in which
objects can be seen in the side
(what we refer to as peripheral)
vision while you focus your eyes on
a central point.
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2.2 VISUAL PERFORMANCE & COMFORT (cont.)
Visual acuity:
▰ This is the ability of the observer to
distinguish fine details (i.e. The clarity or
sharpness of vision).
▰ It increases as the amount of available
light increases.
20/20 vision is a term used to express normal visual acuity (the clarity or sharpness of vision) measured at a distance of
20 feet. If you have 20/20 vision, you can see clearly at 20 feet what should normally be seen at that distance. If you have
20/100 vision, it means that you must be as close as 20 feet to see what a person with normal vision can see at 100 feet.
Having 20/20 vision does not necessarily mean you have perfect vision. 20/20 vision only indicates the sharpness or
clarity of vision at a distance. Other important vision skills, including peripheral awareness or side vision, eye
coordination, depth perception, focusing ability and color vision, contribute to your overall visual ability.
Some people can see well at a distance but are unable to bring nearer objects into focus. This condition can be caused
by hyperopia (farsightedness) or presbyopia (loss of focusing ability). Others can see items that are close but cannot see
those far away. This condition may be caused by myopia (nearsightedness).
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2.2 VISUAL PERFORMANCE & COMFORT (cont.)
Contrast sensitivity:
▰ Contrast is the difference in brightness
or colours between two parts of the
visual field.
▰ Contrast sensitivity is the ability of the
eye to distinguish differences in
luminance and is a function of task
illuminance.
The Pelli Robson contrast sensitivity chart tests your ability to
detect letters that are gradually less contrasted with the white
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background as your eyes move down the chart.
2.3 VISUAL ADAPTATION
Adaptation
Brightness constancy
▰ Adaption is the process occurring as ▰ This is the visual ability to perceive
the eyes adjust to the relative
objects as having the same level of
brightness or colour of objects in the
brightness even though the level of
visual field i.e. the process by which
lighting changes.
the eye adjusts itself to different
luminances.
▰ The cones and the rods on the retina
take a significant amount of time to
reach full sensitivity.
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2.3 VISUAL ADAPTATION (cont.)
Local brightness contrast
▰ Although the eye is capable of
adapting to wide variations in
luminance, it cannot adapt
simultaneously to two very different
levels. The eye minimizes the
problem by trying to focus on one
area of different brightness at a time.
▰
While the eye can adapt to either of
these brightness levels alone, the
adjacency of the two levels in the
field of view is the source of
discomfort and reduced visual acuity.
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2.3 VISUAL ADAPTATION (cont.)
Local brightness contrast (cont.)
▰ To achieve a comfortable brightness
balance, it is desirable and practical to
limit the brightness ratio between
areas of appreciable size (from normal
viewpoints) as follows:
Recommended brightness ratios
Between task and adjacent surroundings
3 to 1
Between task and more remote darker surfaces
10 to 1
Between task and more remote lighter surfaces
0.1 to 1
Between fenestration and adjacent surfaces
20 to 1
Anywhere in the field of vision
40 to 1
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2.3 GLARE AND ITS CONTROL
Glare:
▰ This is the discomfort or impairment
of vision caused by an excessive
range of brightness in the visual field.
▰ It is a visual sensation produced by
surfaces which produce high
luminance gradients within the field of
view.
Categories of glare:
▰ By origin (cause of glare sensation)
❑
Direct glare
Indirect (reflected) glare
By effect on people
❑
▰
❑
Discomfort glare
❑
Disability glare
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2.3 GLARE AND ITS CONTROL (cont.)
a) Direct glare
▰
▰
This is caused by light sources such as
candles, artificial light fittings, or windows
that are directly in the field of view.
It depends on the characteristics of the
space and of light sources (natural or
artificial) directly in the visual field of a
person.
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2.3 GLARE AND ITS CONTROL (cont.)
b) Indirect (reflected) glare
▰
▰
Indirect glare is caused by light that is
reflected to the eye from surfaces that
are in the field of view - often in the task
area.
Veiling reflection is a form of reflected
glare that occurs when the source of
illumination is reflected by a specular
task surface.
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2.3 GLARE AND ITS CONTROL (cont.)
c) Discomfort glare
▰
This is that which causes visual discomfort
without necessarily lessening the ability to
see detail.
▰
Measured by the glare index.
▰
The effects of discomfort glare can be mitigated
by reducing the luminance of the light source,
increasing the luminance of the object being
observed through a better distribution of light and
through the use of lighter colours for the walls,
whose reflection characteristics have a
considerable importance.
Image © Jerusha Ngungui
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2.3 GLARE AND ITS CONTROL (cont.)
c) Disability glare
▰
▰
This is the glare that lessens the ability
to see detail. It does not necessarily
cause visual comfort.
It results from areas in the field of view
of such brilliance that they cause
scattering of light within optical matter
of the eye causing a veiling effect. This
veiling effect reduces visual contrast to
such a degree the seeing is reduced.
Image © Jerusha Ngungui
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2.3 GLARE AND ITS CONTROL (cont.)
c) Disability glare (cont.)
Blinding glare:
is glare which is so intense that for an
appreciable length of time after it has been
removed, no visual perception is possible.
▰
Image © Jerusha Ngungui
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2.3 GLARE AND ITS CONTROL (cont.)
Glare index:
▰ A value for predicting the presence of
glare as a result of daylight entering
an area.
▰ The important variables of glare
index are:
❑
The luminance of the sky as seen
through the window (the larger the
window the higher the index)
❑
The apparent size of the visible area
of the sky (the larger the area the
higher the index)
❑
The position of the visible sky within
the field of view (the closer the
center of vision the higher the index)
❑
The average luminance of the room
excluding the visible sky (the darker
the room the higher the index)
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2.3 GLARE AND ITS CONTROL (cont.)
Strategies for reducing unwanted glare:
▰
limiting the luminance of the sources in the
direction of the eye;
▰
relocating or screening the sources from view;
▰
raising the back ground luminance against
which they are seen;
▰
▰
▰
repositioning the work station;
▰
parabolic louvers, special lenses or other
diffusing media on fixtures that diffuse the
fixture's light output;
▰
changing the surface reflectance of the task;
taking advantage of structural features, such ▰ use blinds or shades on windows to control
the amount or transmittance angle of sunlight
as down stand beams, to conceal fittings from
entering the space.
view;
use of indirect lighting that throws more light
upward than downward, diffusing the light and
reducing glare on computer screens;
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03
DAYLIGHTING
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3.1 DAYLIGHTING BENEFITS
▰
▰
▰
▰
▰
▰
▰
▰
Improved Life-Cycle Cost
Increased User Productivity
Reduced Emissions
Reduced Operating Costs
Provide visual comfort
Reduce amount of energy associated with lighting
Reduce thermal gains indoors caused by artificial lighting
Provide psychological benefit
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3.2 DAYLIGHT AVAILABILITY
Natural Light Sources
▰ Direct sunlight along a straight
path from the sun, through an
opening to a given point;
▰ Diffuse light through the sky
and clouds;
▰ Reflected (albedo) light –
either externally by the ground
and surrounding buildings or
internally by walls, ceilings and
other internal surfaces.
SC – Sky Component (Direct + Diffuse)
ERC – Externally Reflected Component
IRC – Internally Reflected Component
Diffuse
Direct
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3.3 DAYLIGHTING STRATEGIES
a) Side lighting
▰ Provides daylight through apertures
located in the perimeter walls of a
building.
▰ It improves the occupants’ comfort
by creating a visual connection to
the outdoors.
▰ The accessibility of daylight in this
strategy is highly dependent on
building's facade orientation.
▰
▰
Well-oriented apertures can
maximize the daylight harvesting
potential as well as minimizing glare
and solar heat gain.
Problems associated with this
strategy include:
▻
Direct solar heat gain which
may introduce heat gain and
glare issues hence use of
shading elements is important.
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Coca cola Building, Nairobi © Jerusha Ngungui
Strathmore Business School, Nairobi © Jerusha Ngungui
Library, The University of Nottingham, UK © Jerusha Ngungui
3.3 DAYLIGHTING STRATEGIES (cont.)
b) Top lighting
▰ Provides daylight through rooftop
apertures.
▰ These strategies can provide
uniform daylight distribution to the
entire top floor area if the entire top
floor uses rooftop apertures
distributed across the roof area.
▰
Applicable in single storey buildings
or the top floor of a multi-storey
building and they include:
▻
roof monitors
▻
sawtooth roofs
▻
skylights
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3.3 DAYLIGHTING STRATEGIES (cont.)
Roof monitors
▰ Consists of a flat roof section raised
above the adjacent roof, with
vertical glazing on at all sides of the
raised bay.
▰ This arrangement can provide
daylight in all directions, but may
result in higher heat gain.
❑
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3.3 DAYLIGHTING STRATEGIES (cont.)
Sawtooth roofs
▰ These consist a series of either vertical
or sloped glasses, which are separated
by sloped roof elements.
▰ This can be used to uniformly illuminate
a large floor area while minimizing
impacts on building's overall height.
▰ The orientation of the glazing can be
selected to maximize daylight level
while reducing direct solar radiation and
heat gain.
❑
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3.3 DAYLIGHTING STRATEGIES (cont.)
Skylights
▰ These can have many forms including
dome, pitched and flat panels that are
placed in the plane of the building's roof.
▰ Horizontal skylights can be an energy
problem because they receive solar heat
directly at midday.
▰ Integration of louver systems can
control solar heat gain as well as glare
in skylight.
❑
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3.3 DAYLIGHTING STRATEGIES (cont.)
▰
Problems associated with top lighting strategies include:
▻
▻
▻
potential leaks (in the case of poor detailing);
exposure to direct solar radiation (hence heat gains if not properly shaded;
and,
limitation of visual connection between indoors and outdoors.
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Sacred Heart Cathedral, Kericho © Jerusha Ngungui
Charles de Gaulle Airport, France © Zeltia Blanco
Barcelona-El Prat Airport, Spain © Zeltia Blanco
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UN-Habitat offices, Nairobi © UNON
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Library, Catholic University of East Africa © Musau Kimeu
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United Nations Office in Nairobi © Jerusha Ngungui
Ngurdoto Mountain Lodge, Tanzania © Jerusha Ngungui
Two Rivers Mall, Nairobi © Jerusha Ngungui
3.3 DAYLIGHTING STRATEGIES (cont.)
c) Other strategies
Other innovative strategies include the
use of:
▰ Atrium
▰ Light tubes
▰ Light shelves
▰ Anidolic ceilings
▰ Venetian blinds
▰ Translucent materials
Atrium
▰ An atrium designed for maximum
energy savings and efficiency should
incorporate daylighting, ventilation,
and passive heating and cooling
techniques as design features
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UN-Habitat Offices, Nairobi © UNON
3.3 DAYLIGHTING STRATEGIES (cont.)
Light tubes
▰ A light tube is a device used to
capture daylight and reflect it into
the building.
▰ It consists of an outside collector
(usually on the roof), a tube with
high reflectance on the internal
surface and a diffuser.
▰
By using light tubes, daylight can not
only be achieved through the perimeter
zones but also the deep regions of the
rooms.
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LIGHT
TUBES
Heliostats
Reflective tubes
Diffusers
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The University of Nottingham, UK © Jerusha Ngungui
3.3 DAYLIGHTING STRATEGIES (cont.)
Light shelves
▰ The “light shelf” is a well established
way to facilitate the penetration of
light into a room .
▰ The light shelf is generally made of a
horizontal or nearly horizontal shelf
arranged on the outside and/or
inside of the window, in its upper
part.
▰
It must be positioned so as to avoid
glare and maintain the view outside; in
general, the lower the light shelf, the
greater the glare.
76
77
3.3 DAYLIGHTING STRATEGIES (cont.)
Anidolic ceiling
▰ This strategy uses parabolic
concentrators to collect diffuse daylight
which is distributed to the back of a
room through a specular light duct
located above a ceiling plane.
▰ Outside the building, an optical anidolic
concentrator captures and focuses the
scattered light coming from the highest
part of the sky, which is the brightest on
overcast days;
▰
a light pipe arranged in the ceiling, carries
the light into the back of the room.
▰
Corresponding with the outlet of the pipe
in the back of the room, a parabolic
reflector distributes light into the lower
parts of the room
78
79
3.3 DAYLIGHTING STRATEGIES (cont.)
Venetian blinds
▰ Have dual purpose of providing shade
and indirect lighting.
▰ The slats may be flat or curved, and can
be placed outside, inside or in the cavity
of double glass (not recommended,
since they become very hot and reradiate towards the inner pane, which
warms up).
▰ In any of these positions, they must be
reflective in order to redirect light.
▰
There are several types of slats that
are able to redirect light:
▻
fixed or mobile,
▻
solid or micro perforated.
80
81
3.3 DAYLIGHTING STRATEGIES (cont.)
Translucent materials
▰ These may be used in place of
glass to admit diffused light
into a space with no direct sun.
▰ Common in warehouses,
factories etc.
Tile & Carpet Center Warehouse, Nairobi © Jerusha Ngungui
82
3.4 LIGHTING: PERIPHERAL + CORE ZONES
In any building, two separate problems can be distinguished:
▰ the lighting of the peripheral zones or premises, which have contact with the skin of
the building and therefore the possibility of direct access to the light outside; and
▰ that of the interior zones or premises, without contact with the shell, where the only
access to natural light is by means of some system of transportation..
CORE ZONE
PERIPHERAL ZONE
83
3.4 LIGHTING: PERIPHERAL + CORE ZONES (cont.)
General aspects that affect the buildings interrelation with light:
a) Compactness of the building:
▰ Establishes the relationship between the outer shell of the building and its
volume, i.e., the degree of concentration of the interior spaces.
84
3.4 LIGHTING: PERIPHERAL + CORE ZONES (cont.)
b) Porosity of the building:
▰ Refers to the existence within its global volume of empty spaces and points of
communication with the exterior, such as courtyards.
85
3.4 LIGHTING: PERIPHERAL + CORE ZONES (cont.)
c) Transparency of the skin of the
building:
▰ Varies from totally opaque buildings
to totally glazed ones.
▰ Although greater transparency
increases light in the peripheral zone,
good lighting depends more on the
appropriate distribution of light than
on quantity.
86
3.4 LIGHTING: PERIPHERAL + CORE ZONES (cont.)
d) Size of the building:
▰ Though the size of a building does not in principle have any influence on the
distribution of light in its interior; areas of identical shape but different size and with
their openings to scale with their size will have the same interior light distribution.
▰ Spaces with large surface area will have a dark central zone unless they preserve
their proportions by having a higher ceiling.
87
3.4 LIGHTING: PERIPHERAL + CORE ZONES (cont.)
e) Shapes and proportions of a building:
▰ Depending on the location of the windows, the shape and proportion of the
building is important.
▰ As a rule, irregular or elongated spaces with light entering at the end have a
rather irregular light distribution
88
3.4 LIGHTING: PERIPHERAL + CORE ZONES (cont.)
e) Shapes and proportions of a building (cont.):
▰ Lateral entry of light into a space causes a rapid decrease in light (i.e., illuminance)
the further we are from the opening, due to the fact that the angle of vision of the
sky (the main source of light) is soon lost. This results in peripheral zones and
premises easily being badly lit, even if the total amount of light present is
sufficient. The entry of zenithal light, on the other hand, tends to be more suitable.
Lateral light
Zenithal light
89
3.5 ENHANCING DAYLIGHT IN BUILDINGS
Through the use of:
▰ Exterior shading and control devices:
have a dual purpose of reducing heat
gain and diffusing natural light before
entering a space.
▰ Glazing materials are the simplest
method to maximize daylight within a
space is to increase the glazing area.
▻
U-value: represents the rate of heat transfer
due to temperature difference through a
particular glazing material.
▻
Solar Heat Gain Coefficient: the fraction of
incident solar radiation (for the full
spectrum) which passes though an entire
window assembly, including the frame, at a
specified angle. Range is 0-0.85. A higher
SHGC is preferred in solar heating
applications to capture maximum sun,
whereas in cooling applications, a low
SHGC reduces unwanted solar heat gain.
▻
Visible Light Transmittance: a measure of
how much visible light is transmitted
through a given glazing material.
90
3.5 ENHANCING DAYLIGHT IN BUILDINGS (cont.)
▰
▰
Other lighting control schemes:
Simple side lighting strategies allow
daylight to enter a space and can also
serve to facilitate views and
ventilation.
Reflectance values of room surfaces
should be kept as high as possible ceiling over 80%, walls over 50%, and
floors around 20%.
▰
Integration with electric lighting
controls (daylight controls) such as:
▻
Switching controls—on/off controls simply
turn the electric lights off when there is
ample daylight.
▻
Stepped controls—provide intermediate
levels of electric lighting by controlling
individual lamps within a luminaire.
▻
Dimming controls—continuously adjust
electric lighting by modulating the power
input to lamps to complement the
illumination level provided by daylight.
91
92
All images © Jerusha Ngungui
3.5 ENHANCING DAYLIGHT IN BUILDINGS (cont.)
▰
Other lighting control systems that
include:
Occupancy controls
▻
▻
using infrared, ultrasonic or micro-wave
technology, occupancy sensors respond to
movement or object surface temperature
and automatically turn off or dim down
luminaires when rooms are left unoccupied.
Typical savings have been reported to be in
the 10 to 50 percent range depending on
the application.
Timers
▻
These devices are simply time clocks that
are scheduled to turn lamps or lighting
circuits off on a set schedule.
▻
They are extremely cost effective devices
especially for spaces that are known to be
unoccupied during certain periods of time.
93
3.5 CONTROL ELEMENTS
▰
▰
Are specially designed to enhance and/or control the entry of natural light.
They can also serve other environmental purposes such as:
▻
ventilation,
▻
the possibility of a controlled view,
▻
the thermal protection of the interior or
▻
the safety of the building.
94
3.5 CONTROL ELEMENTS (cont.)
a) Separator surfaces
▰ These are surface elements of transparent or translucent material,
incorporated into a transmitting element that separates two different
environments.
▰ They enable radiation, and sometimes the view of the exterior, to pass through,
but block the passage of air.
▰ They can be transparent, chemically or mechanically treated surfaces, those
that follow a particular geometrical pattern and active enclosing surfaces.
95
96
Arab World Institute © Zeltia Blanco
3.5 CONTROL ELEMENTS (cont.)
b) Flexible screens
▰ These are elements that partially or totally prevent the entry of solar radiation
and make the light that shines through them diffuse.
▰ Depending how they are placed, they can allow ventilation and provide visual
privacy. They can be retracted, rolled up or folded away to remove their
influence when so wished.
▰ These screens can be placed over the external surface of a transmitting
element, so as to selectively prevent radiation passing prior to entry or, by
placing them over the interior of separator surfaces, control the radiation that
has already entered the transmitting element and is illuminating the interior.
97
© https://windowsdressedup.com
98
3.5 CONTROL ELEMENTS (cont.)
c) Rigid screens
▰ These are opaque elements that redirect and/or block the direct solar radiation
that might otherwise strike a transmitting element.
▰ Normally, they are fixed and unadjustable, though there may be exceptions to
this.
▰ Their main variable is their position with relation to the opening they protect.
99
100
Kenidia House (left) and Parliament Building (right) in Nairobi © Jerusha Ngungui
3.5 CONTROL ELEMENTS (cont.)
d) Solar filters
▰ These are surface elements that cover all, or nearly all, of the outer face of a
transmitting element, protect it from solar radiation and allowing ventilation.
▰ They can be fixed or movable (so that they can be removed and the opening
left free), and adjustable if the orientation of the louvers can be changed.
101
102
© http://www.fotoventasdigital.com/Ga/82715/u9ax0g-modern-sun-protection/82649/
3.5 CONTROL ELEMENTS (cont.)
e) Solar obstructors
▰ These are surface elements composed of opaque materials, and can be
attached to the opening of a transmitting element in order to completely seal
it.
▰ They are normally called shutters and can be located either on the exterior or
on the interior of a glass separator surface.
103
104
Technical University of Mombasa © Jerusha Ngungui
3.2 DAYLIGHT AVAILABILITY
105
All images © Jerusha Ngungui
3.6 Conditions of the sky
Luminance at point B = B cd/m2
a) Uniform Standard Sky (Overcast sky):
▰ This is an overcast sky that has the
same luminance in every direction.
▰ The relationship between the mean
luminance of the sky and the illuminance
of a horizontal plane without any
obstruction will be:
(It is taken to be constant for all angles as viewed by the Observer)
Illuminance (E) at Observer = πB lux
B
B
Eh= 𝝅𝑳
where:
Eh = illuminance on horizontal plane (lux)
L = mean illuminance of the sky (cd
m-2)
B
B
B
B
B
B
B
B
B
106
3.6 Conditions of the sky (cont.)
b) CIE (Commission Internationale d’Eclairage)
Standard Overcast Sky:
▰ This is a model of an overcast sky in
which the illuminance steadily rises
above the horizon.
Luminance at point BB= = BZ
(1 + 2 sin  )
Bz
3
(It is taken to be constant for all angles as viewed by the
observer)
Where:
B = Luminance at a height with angle  above the horizon (cd/m2)
 = Angle above the horizon
Bz = Luminance at zenith
Luminance at Zenith = 3 times brighter than at the horizon
107
3.6 Conditions of the sky (cont.)
Importance of CIE Model
▰ If the daylight level indoors is adequate on an overcast day, it is likely to be
sufficient on a sunny day too.
▰ It avoids the complication of taking orientation into account: on an overcast
day, the sky luminance pattern is independent of the compass point.
▰ Although the illuminance, inside and outside, varies continuously, the
illuminance at a given point indoors under overcast conditions is a fairly
constant fraction of the prevailing outdoor illuminance.
108
3.6 Conditions of the sky (cont.)
c) Clear sky:
▰
Considers the direct incidence of the sun,
with an intensity in the order of 100,000
cd/m2 and the position corresponding to
the time of the year and day.
▰
The rest of the sky dome and reflection
from other surfaces on the ground or other
external elements (albedo) can also be
considered as indirect sources.
▰
For the case of a clear sky dome,
luminance decreases as we move away
from the sun, with values varying between
2000 and 9000 cd/m2.
d) Cloudy sky:
▰
Cloudy sky has more than 70 % cloud
cover. It normally excludes the sun.
▰
In the case of a cloudy sky, intermediate
between a clear and an overcast sky,
hypotheses must be made which
correspond to a situation somewhere
between those considered in the above
cases.
109
3.7 Daylight Factor
▰
▰
Ratio between the actual
illuminance at a point inside a
room and the illuminance from an
unobstructed hemisphere of the
same sky.
Expressed as a percentage
𝐸𝑖
𝐷𝐹 =
𝑥 100
𝐸𝑜
Where:
𝐷𝐹 = daylight factor at a chosen reference point in the room (%)
𝐸𝑖 = illumination at the reference point (lx)
𝐸𝑜 = illumination at that point if the sky was unobstructed (lx)
110
3.7 Daylight Factor (cont.)
Daylight factor components
▰
▰
▰
Sky Component (SC)
Externally Reflected Component
(ERC)
Internally Reflected Component
(IRC)
𝐷𝐹 = 𝑆𝐶 + 𝐸𝑅𝐶 + 𝐼𝑅𝐶
SC – Sky Component (Direct + Diffuse)
ERC – Externally Reflected Component
IRC – Internally Reflected Component
Diffuse
Direct
111
3.7 Daylight Factor (cont.)
a) Sky Component
▰ Area of the sky visible from the
reference point inside the room and
its average altitude angle;
▰ Window size and position in relation
to the reference point;
▰ Thickness of window frame;
▰ Quality of the glass and its clearness;
▰ Any external obstructions.
112
3.7 Daylight Factor (cont.)
b) Externally Reflected Component
▰ The area of the obstruction as seen
through the window from the
reference point
▰ Includes the reflectance of these
obstructing surfaces.
Obstructions
(buildings, trees etc.)
113
3.7 Daylight Factor (cont.)
c) Internally Reflected Component
▰ Considers:
o
o
o
The size of the room;
Surface areas in relation to
the window / opening sizes;
Surface reflectance.
114
3.7 Daylight Factor (cont.)
1%
Window size, shape & position and DF
▰ The size of the window and its location
on a wall affects the light distribution.
▰ The taller the window for a given
width, the larger the sky component
and the deeper the daylight factors
contours are pushed back.
▰ Wide windows give better distribution
across the width of the room but do
not produce such high DF if their
height is limited.
21.4%
115
3.7 Daylight Factor (cont.)
A
Window design for tall
narrow windows
B
Window design for
long, high windows
116
3.7 Daylight Factor (cont.)
117
3.7 Daylight Factor (cont.)
118
3.7 Daylight Factor (cont.)
119
3.7 Daylight Factor (cont.)
DESIGN SKY
▰ Design Sky values are derived from a
statistical analysis of outdoor illuminance
levels.
▰ They represent the horizontal illuminance
that is exceeded 85% of the time between
9 am and 5 pm throughout the year.
▰ They offer a WORST CASE scenario that
you can design to and be sure you meet
the desired light levels at least 85% of the
time.
▰
❑
❑
❑
Typical Design Sky Illumination
values:
Nairobi latitude 10 S – 18,000 lux
Sydney latitude 330 S – 8,000 lux
London latitude 520 N – 5,000 lux
120
3.7 Daylight Factor (cont.)
Example
▰ Establish required illumination level, E;
▰ Ascertain local “Design Sky” illumination,
Eo
▰ Calculate necessary daylight factor.
▰ Manipulate the design variables (window
size etc.) to achieve this daylight factor.
IF:
𝐸𝑖 = 300 lx illumination at the reference point (lx)
𝐸𝑜 = 18000 lx (Nairobi)
Then:
𝐷𝐹 =
300
18000
𝑥 100 = 1.7%
121
3.8 Buildings and daylighting
a)
▰
▰
▰
▰
Building form + room dimensions
Well-oriented buildings maximize daylighting through building
facades reducing the need for artificial lighting.
Orienting the long axis of the building in the east/west
direction will maximize the amount of northern and southern
facades.
The form of the building determines the quality of daylight
experienced within the space.
Linear forms with narrow widths have a great potential for
daylighting through side lighting than square shaped plans.
122
3.8 Buildings and daylighting (cont.)
b)
▰
▰
Limiting depth
The depth to which natural
light penetrates into a room is
influenced by the window head
height.
Light penetration is twice the
head height of the window
(with shading).
123
3.8 Buildings and daylighting (cont.)
c)
Fenestrations
Some design considerations:
▰ The window head should be as high as
possible, say at least 2 m above floor level, to
enable one to see out when standing.
▰ The window sill should not be higher than 1 m
from floor level to enable one to see out when
sitting.
▰ The window surface area should be evenly
distributed over the outside wall and the
window heights and widths should not be too
small in relating to the window wall because
this reduces the uniformity of lighting and
produces undesirable shadows.
▰ Better lighting can be achieved with windows
on opposite walls since the illumination
produced by the individual windows are
superimposed. The region with the minimum
daylight factor is then displaced towards the
centre of the room. The usable depth of the
room thus increases.
124
3.8 Buildings and daylighting (cont.)
d)
▰
Glazing and reflectors
Clear glass is fairly uniformly transparent to all wavelengths of solar radiation:
❑ Good for natural lighting - An object inside looks - chromatically – the same as outside;
❑ Good for passive heating in cold climates/seasons. In hot climates/seasons, it has to be shaded to
minimize heat gains.
▰
Tinted glass changes the solar spectrum.
❑ Not only reduces natural lighting, but also increases the thermal discomfort of the occupants on
sunny days.
▰
Grey and bronze glass, reduce the effect of the radiation (low transmission), but
does not alter the spectrum in any appreciable way.
125
3.8 Buildings and daylighting (cont.)
d)
▰
Glazing and reflectors (cont.)
‘Heat-absorbing’ glass contains chemicals that react to heat by absorbing solar
energy. It also selectively reduces the transmittance of visible light.
❑ May result in energy savings.
▰
▰
▰
▰
Light reflecting film reduces heat gain without reducing the amount of incoming
natural light.
Room infrared reflecting films
Solar infrared reflecting films
IR transparent plastic
126
3.8 Buildings and daylighting (cont.)
e)
Obstructions
▰
Any obstruction (buildings opposite the window, trees, etc.) decreases the illuminance
in rooms.
▰
Obstructions which subtend elevation angles of more than 25-30° significantly reduce
the daylight penetration. This can be improved by increasing the height and width of the
window.
▰
If possible, the angle subtended by obstructions should not be greater than 30°.
▰
The minimum distances between adjacent building and the window as laid down in the
building regulations should be complied with.
127
3.8 Buildings and daylighting (cont.)
f)
▰
▰
Uniformity of lighting
Uniformity is essentially dependent on:
(a) the dimensions of the room, the windows and all the obstructions to light,
(b) the reflectances of the surfaces enclosing the room, the obstructions to
light and the room furnishings, as well as the type of glazing.
The uniformity of illumination is expressed in terms of the ratio of the minimum
illuminance in the room to the average illuminance measured on a horizontal
reference plane.
128
3.8 Buildings and daylighting (cont.)
g)
▰
Glare
The degree of glare thus depends on :
▻
▻
the luminance and the size of the light-emitting surface seen by the eye,
the ratio of this luminance to the luminance of this environment or
background,
the distance of the glare-producing surface from the eye and its position in
the field of vision.
All types of glare, both direct glare from the sun and glare from reflections, e.g.
from polished floors, are to be avoided.
▻
▰
129
3.8 Buildings and daylighting (cont.)
h)
▰
▰
▰
Shadow intensity and direction of incident light
For the perception of the solidity and surface texture of objects a reasonable
shadow intensity is required.
Adequate shadow intensity is generally provided by the lateral incidence of
daylight into rooms with side windows.
Working positions should be arranged so that hand and body shadows do not fall
on the working surface.
130
3.9 Climate and daylighting
Hot-Dry climates
▰
▰
▰
▰
Direct sunlight should be excluded from buildings for
thermal reasons and to avoid glare.
Internally reflected light is the best for natural lighting, a
window positioned high, i.e. above eye level for example,
will have the effect of reflecting the light towards the
ceiling.
A ceiling painted white will, in turn, provide adequate
diffusion of light inside, even if the openings are
relatively small.
Low windows are also acceptable if they face a shaded
courtyard or non-glaring surfaces.
131
3.9 Climate and daylighting (cont.)
Hot/Warm-humid climates
▰
The main source of glare is the sky.
▰
Direct sunlight should be excluded
for thermal reasons.
▰
Heat should be kept away through
cross ventilation via large openings.
▰
These openings should be positioned
in such a way that the sky is not
directly seen.
▰
Overhanging roofs, large verandas or
vegetation can be used for
obstructing the direct view of the sky.
132
3.10 Daylighting and shading
▰
▰
Well-designed sun control and
shading devices can dramatically
reduce building peak heat gain and
cooling requirements and improve
the natural lighting quality of building
interiors.
They can also improve user visual
comfort by controlling glare and
reducing contrast ratios.
▰
Solar control and shading can be
provided by a wide range of building
components including:
❑
Landscape features such as mature
trees or hedge rows;
❑
Overhangs or vertical fins;
❑
Light shelves;
❑
Low shading coefficient (SC) glass;
❑
Interior glare control devices such as
Venetian blinds or adjustable louvers.133
3.10 Daylighting and shading (cont.)
Light shelves
▰ The “light shelf” is a well established way to
facilitate the penetration of light into a room
▰ The light shelf is generally made of a
horizontal or nearly horizontal shelf
arranged on the outside and/or inside of the
window, in its upper part.
▰ It must be positioned so as to avoid glare
and maintain the view outside; in general,
the lower the light shelf, the greater the
glare.
134
3.10 Daylighting and shading (cont.)
The minimum depth of an external light
shelf is determined by the shading
requirements; the deeper the shelf, the
better it shades the window below,
preventing the penetration of direct
radiation, which causes glare and solar
gains.
For the interior light shelf, the limiting
factor is still the glare; i.e. it is necessary
to prevent the penetration of direct
radiation.
If the optimum depth of the external light
shelf is excessive in relation to other
needs, the same result can be obtained
by recessing the window; with this type
of solution the contribution of natural
light can be further increased by
appropriately tilting the sill.
135
3.11 PSALI
▰
▰
PSALI - Permanent Supplementary
Artificial Lighting of the Interiors
was developed to light deep rooms
that would not otherwise have
adequate daylight.
The objective of PSALI schemes is
to integrate artificial lighting with
daylighting in order to compensate
for the relative lack of daylight in
those parts of a room, which are
remote from the windows.
▰
PSALI is based on three principles:
❑
❑
❑
Utilisation of daylight as far as
practicable,
Use of electric lighting to
supplement the daylight in the
interior parts of the room,
Installation of the electric lighting
in such a way that the daylight
character of the room is retained.
136
3.11 PSALI (cont.)
Guidance on PSALI
▰ PSALI zone starts where the DF falls to
10% of that at a distance Hf/5 from the
window where Hf is the height of the
window head above the floor.
▰ Illuminance level (E) to be provided by
artificial lighting in the PSALI zone
based on the formula
𝑬 = 𝟓𝟎𝟎𝑫 𝑳𝒖𝒙
Where D = average DF in the PSALI zone
137
3.11 PSALI (cont.)
138