Course: Climate Responsive Design (3672) Semester: Spring, 2020

ASSIGNMENT - 1

Q.4 “Lighting is a significant factor to achieve Visual Comfort.” Explain the

statement with examples focusing on natural light optimization.
1. Introduction
Natural light is irreplaceable because it is a full spectrum light, it changes during the day and
it is different every day of the year. A variable illumination throughout the day, in terms of
intensity and colour temperature, creates dynamic indoor environments that are more pleasant
for people. Daylight needs to be controlled, especially in office buildings, to avoid discomfort
glare and high luminance reflections on display screens, to provide a good lighting level even
in the deeper part of a room and to reduce cooling loads. To improve the quality of light, of
visual comfort and to minimize lighting, heating and cooling loads advanced daylighting
systems (such as BMS, Building Management Systems) and external shadings should be
used. The aim of this study is to optimize the availability of glare-free natural daylight in a
building’s interior, in order to create spaces of high visual quality, where the energy demand
for artificial lighting and cooling can be reduced by means of control strategies and shading
devices. The same office room has been supposed at different latitudes, since each latitude
needs a specific shading system. The lighting simulation has been carried out with the
software Daysim, developed by the National Research Council del Canada and by the
Fraunhofer Institute for Solar Energy Systems and the software Radiance, developed by Greg
Ward and by the Lighting System Research group of the Lawrence Berkeley Laboratory.

People spend large amount of their time indoors and, without proper light, they may have
physiological and psychological problems, which in some cases can cause sickness (Boyce,
1998; IEA, 2000). Many studies have demonstrated that if daylight is the primary source of
lighting, there is a great improvement in productivity, performance and wellbeing in general
(De Carli, De Giuli et al., 2008). Natural light, in fact, has both direct and indirect effects on
human beings: the direct effects are caused by chemical change in tissues due to the energy of
the absorbed light, while the indirect ones concern the regulation of the basic biological
functions and the production of hormones, connected to light exposure. Therefore, to improve
well-being, satisfaction and productivity, especially in office buildings, it is very important to
project indoor spaces with specific attention to workers’ comfort. This paper shows the
results, in terms of visual lighting requirements, of the application of some shading devices in
a office room, located in five different latitudes: Stockholm (59°65' N), Venice (45°50' N), El
Cairo (30°13' N), Bombay (19°12' N) and Colombo (6°82' N). Solar shading devices are
often used in buildings to reduce overheating, to control glare from windows and to provide
privacy. The control of daylighting is very important especially in office buildings because of
its relationship with occupants’ satisfaction and performance. On the other hand, lighting and
blind control systems can reduce energy demand for artificial lighting, which can contribute
to the development of environmentally sustainable buildings.
Day lighting is the controlled admission of natural light, direct sunlight, and diffused skylight
into a building to reduce electric lighting and saving energy. By providing a direct link to the
dynamic and perpetually evolving patterns of outdoor illumination, day lighting helps create

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a visually stimulating and productive environment for building occupants, while reducing as
much as one-third of total building energy costs.

Figure 1: Use of Natural light at some working station

Visual Comfort
The analysis of energy savings obtained by different lighting and shading control strategies,
the dynamic daylight performance parameters and the annual illuminance profiles inside the
office have been performed with the software DAYSIM (Reinhart, 2005). The model
DAYSIM can predict the energy requirement for artificial lighting and indoor illuminance
profiles under all appearing sky conditions throughout the year – the so-called “All weather
sky model” (Perez et al., 1993). These profiles are based on a weather climate file and they
can be coupled with a stochastic user behaviour model, to predict some daylight performance
indicators, such as daylight autonomy, annual light exposure and lighting energy use for
different lighting and shading control strategies. The energy requirement for artificial lighting
depends on the user behaviour and on the control strategies for lighting and shading systems.
The user behaviour implemented in DAYSIM is based on a model, called Light switch
(Reinhart, 2004), which is the result of some studies in buildings throughout the Western
world. These behaviour models mimic how users interact with personal controls (light
switches, blinds, window opening). In this study three different user behaviours have been
considered, for both lighting and blind control: passive, active and mix. A passive user is
defined as a “user who keeps the electric lighting on throughout the working day and keeps
the blinds partly closed throughout the year to avoid direct sunlight”. An active user is a “user
who operates the electric lighting in relation to ambient daylight conditions, open the blinds
in the morning and partly closes them during the day to avoid direct sunlight”. The mixed
user behaviour is the mix of both active and passive behaviours. For each different user,
different lighting control strategies have been considered.

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 Figure 2: A sample of Visual Comfort Lighting Environment

A day lighting system consists of systems, technologies, and architecture. While not all of
these components are required for everyday lighting system or design, one or more of the
following are typically present:
 Daylight-optimized building footprint
 Climate-responsive window-to-wall area ratio
 High-performance glazing
 Daylighting-optimized fenestration design
 Skylights (passive or active)
 Tubular daylight devices
 Daylight redirection devices
 Solar shading devices
 Interior designs (Plantation, furniture design, space adjustment planning, room
finishes etc)

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 Figure 3: Visual Comfort supporting Room Sitting Arrangement

daylighting systems are necessary to control visual environment, because they provide solar
shading, protection from glare and redirection of light. Each latitude needs different shading
devices: in high latitudes (Stockholm), cloudy skies are predominant and the exterior
illuminance on winter days at noon is often even less than 5000 lux, while a realistic
horizontal illuminance for a brightest overcast sky is about 10000 lux. In these latitudes light
shelves are not enough, while for low latitudes they can correctly control visual comfort in
indoors. On the other hand, daylighting systems can reduce peak demand especially during
summer peak periods, when there is a good daylight availability: if no shading device is
provided, solar heat gains can increase the cooling load. The optimization of the use of BMS
system, integrated with daylight, can save energy, both for artificial lighting and cooling
demand: they can reduce electric power for artificial lighting from 31 % to 73 %, supposing a
mixed user behaviour, depending on control strategies and site latitude. The evaluation of
sustainable buildings cannot be drawn without considering how the occupant behaves and
interact with the environment, in terms of shading and lighting control. In many office
buildings it happens that people work with the light switched on, leaving the blinds down,
even when there is no possibility of glare appearance (Rea, 1984). Simulations carried out in
this work, confirm that the combination “passive user” and “manual control” is responsible of
a non efficient building. For that reason an automated lighting and shading control system
should be provided. The actual Standards evaluate the amount of daylight entering a space by
means of the daylight factor, a parameter that is just a “quantitative” information, not
sufficient to evaluate the “quality” of light (i.e. a complete glazed building would reach a
very high DF, but it would have many problems, in terms of thermal comfort and energy
consumption). The software DAYSIM is very useful, since it includes a behaviour occupancy
model and it can help the designer to analyse and compare critically the impact of different
shading devices and control strategies, by means of some dynamic daylighting metrics.
Finally, the concept of visual comfort depends on people and a lighting condition can be
acceptable for a person but not for another. The Standards try to give some suggestions with

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the purpose to create a acceptable and safe environment, but they miss many aspects (i.e.
people preferences and behaviour, etc). It would have been interesting to compare these
simulation results by directly measuring the illuminance values in a real office room, asking
the occupants, by means of questionnaires, how they feel in those conditions, which shading
they prefer and how and if they operate the lighting and shading systems.

Reference:
1. http://www.ibpsa.org/proceedings/BS2009/BS09_1797_1805.pdf
2. Class Lectures

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