9789144125770

Daylighting and lighting UNDER A NORDIC SKY

Marie-Claude Dubois Niko Gentile Thorbjรถrn Laike Iason Bournas Malin Alenius

ARQ is a foundation that promotes scientific research in architecture, urban planning, building planning and design. ARQ acts as a link between academic researchers and researchers in private practice through cross-border studies and projects.

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Art. No 39919 ISBN 978-91-44-12577-0 First edition 1:1 © The authors and Studentlitteratur 2019 studentlitteratur.se Studentlitteratur AB, Lund Book design: Jesper Sjöstrand/Metamorf Design Cover design: Jesper Sjöstrand Cover photo: Mikael Rutberg (Umeå School of Architecture, White Arkitekter/Henning Larsen) Printed by Dimograf, Poland 2019

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CONTENTS

Preface 9 Acknowledgments 11 About the Authors 13 List of symbols 15 List of abbreviations 19

1 Introduction 25 1.1 1.2 1.3 1.4 1.5

Importance of light and daylight 27 Definition of good daylighting 28 Preference for daylight 28 Benefits of daylighting 29 Risks of daylighting 34

2 Historical perspective on daylighting 39 Vernacular architecture 41 Ancient civilizations 42 2.2.1 Ancient Egypt (3100 BC−332 BC) 43 2.3 Classical antiquity 43 2.3.1 Ancient Greek architecture (490 BC−30 BC) 43 2.3.2 Ancient Roman architecture (509 BC−4th century AD) 44 2.4 Middle Ages 49 2.4.1 Romanesque architecture (6−11th century) 49 2.4.2 Gothic architecture (12–16th century) 50 2.5 Renaissance (14−17th century) 52 2.6 Baroque architecture (17th century) 55 2.7 Industrial Revolution (1760–1850) 56 2.8 Modern architecture (1900−1980) 61 2.8.1 Modern architecture in the Nordic countries 65 2.9 Transition to sustainable architecture 69 2.10 Contemporary architecture 72 2.10.1 Building regulations 74 2.10.2 Voluntary environmental certification systems 75

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2.1 2.2

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Contents

3 Visual effects of light 79 3.1 3.2

Visual perception 81 Visual system 85 3.2.1 Human eye 87 3.2.2 Colour vision 90 3.2.3 Visual field 91 3.2.4 Adaptation 95 3.2.5 Accommodation 101 3.2.6 Glare 102 3.2.7 Veiling reflections 104 3.2.8 Flicker 105

4 Non-visual effects of light 109 4.1 4.2 4.3 4.4 4.5

Psychophysiological background 111 Practical implications 113 Subliminal flicker 116 View outdoors 117 Conclusions 118

5 Photometry 121

5.2

5.3

Definitions and units 123 5.1.1 Luminous flux 124 5.1.2 Luminous intensity 125 5.1.3 Illuminance 126 5.1.4 Luminance 127 5.1.5 Luminous exitance or emittance 128 5.1.6 Brightness 128 Laws of illumination 129 5.2.1 Inverse square law 129 5.2.2 Lambert’s cosine law 130 Reflection and transmission 130

6 Colour 133 6.1 6.2

6.3

Colour perception 135 CIE Colorimetry system 136 6.2.1 Correlated Colour Temperature 140 6.2.2 Colour Rendering Index 142 Colour ordering systems 143

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5.1

Contents

7 Fundamentals of daylighting 147 7.1

7.2

7.3

Daylight sources 149 7.1.1 Sunlight or direct light 149 7.1.2 Skylight or diffuse light 157 7.1.3 Reflected light 161 Standard sky models 164 7.2.1 CIE standard overcast sky (1955) 165 7.2.2 CIE standard clear sky (1996) 167 7.2.3 CIE standard general sky (2003) 168 7.2.4 Perez all weather sky model (1993) 171 Daylight performance metrics 172 7.3.1 Static daylight metrics 173 7.3.2 Dynamic Daylight Metrics 180

8 Daylight quality 189 8.1 8.2

8.3

8.4

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8.5

Daylight quality models 192 Visual model for light in space 196 8.2.1 Contrast and border 197 8.2.2 To perceive space and to see details 198 8.2.3 Seven basic visual terms for defining light in space 200 8.2.4 Visual appraisal – methods and tools used in the design process 204 Simplified quantitative daylight quality model for early design phase 204 8.3.1 Luminance 207 8.3.2 Illuminance 215 8.3.3 Glare 222 8.3.4 Directionality 226 Future of light quality assessment 228 8.4.1 Mean room surface exitance 228 8.4.2 Local contrast and luminance gradient 230 Conclusion 231

9 Daylighting design strategies 237 9.1

Side-lighting 242 9.1.1 Climate and site 242 9.1.2 Orientation 252 9.1.3 Room depth 259 9.1.4 Window size, shape and position 262 9.1.5 Window niche and frame 271 9.1.6 Window glazing properties 275 9.1.7 Visual protection devices 279

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Contents

9.2

9.1.8 Indoor and outdoor reflectances 283 9.1.9 Light distribution 287 9.1.10 Use of glass in intermediate partitions 289 Top-lighting 292 9.2.1 Atria 293 9.2.2 Skylights 305 9.2.3 Light wells 317 9.2.4 Tubular Daylighting Devices 318 9.2.5 Fibre optic lighting systems 319

10 Electric lighting 327

11 Measuring light 361 11.1 11.2 11.3 11.4

Measuring daylight illuminance and daylight factor 363 Measuring luminance 365 Measuring glare 366 Measuring surface reflectance and transmittance 369

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10.1 Electric light sources 329 10.1.1 Properties of light sources 330 10.1.2 Incandescent and halogen sources 332 10.1.3 Fluorescent and compact fluorescent sources 334 10.1.4 Light-Emitting Diode (LED) 336 10.1.5 Other light sources for indoor applications 338 10.2 Luminaires 339 10.3 Lighting control systems 342 10.3.1 Manual controls 345 10.3.2 Occupancy strategies 346 10.3.3 Daylight-linked systems 347 10.3.4 Colour tuning 348 10.3.5 Control networks and integration in the BMS 349 10.4 Strategies for saving electric lighting energy 350 10.4.1 Improvement in lamp and luminaire technology 351 10.4.2 Use of lighting controls 352 10.4.3 Use of Task/Ambient Lighting 353 10.4.4 Improvement in Maintenance Factor 354 10.4.5 Lighting in a circular economy 355

Contents

12 Introduction to daylight simulation 371 12.1 Background 373 12.2 Fundamental elements of daylight simulation 373 12.3 Daylight simulation scene 375 12.3.1 Surroundings 375 12.3.2 Ground 377 12.3.3 Analyzed building 378 12.4 Sky Model 380 12.5 Areas of interest 383 12.6 Space usage 384 12.7 Simulation engine 385 12.7.1 BRE split flux method 385 12.7.2 Rendering Equation 386 12.7.3 Radiosity 387 12.7.4 Raytracing 389 12.7.5 Photon mapping 391 12.8 Annual daylight simulations 392 12.8.1 Daylight coefficients 393 12.8.2 Bidirectional Transmittance Distribution Function 395 12.8.3 Matrix multiplication techniques 397 12.9 Simulation quality control 399

13 Observer based lighting assessment 405

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13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 Index 417

Human perception 407 Measurement 408 Quality of measurements 410 Development of an instrument for measuring light quality 410 Description of the instrument 412 How to use the instrument 413 How to interpret the data 414 Other methods 414

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PREFACE

After nearly a century of electric lighting dominating the design of building interiors, a return to the use of daylight as the main ambient light source in buildings appears motivated by energy, environmental, and health issues. This return to daylighting demands that we recall the old principles of building design, which have influenced the development of architecture throughout history. We must also take into consideration the new context of increasing urban density, demanding building regulations and certifications, evolving computer intelligence and simulation tools, in addition to state-of-the-art electric lighting technologies available today such as LEDs and advanced control systems.

This book was written to provide the minimum background and knowledge to be able to tackle the challenging endeavor of illuminating buildings with daylight as main light source supplemented by energyefficient electric lighting systems. We wrote this book with the intention to support our teaching of a course on daylighting and electric lighting of buildings within the international Master on Energy-Efficient and Environmental Building Design at Lund University. We hope that students will find this book both inspiring and helpful in their study of this vast and interesting subject. We also hope that this book will spark interest amongst building practitioners who wish to devote more time and space to good daylighting design.

Light is generally more important to people in the Nordic countries because it is scarce for a large part of the year and over abundant around the summer solstice. Our lives in the North are significantly influenced by the daily variations of daylight throughout the seasons. The unique character of daylight of the Nordic sky, with its weak intensity and thick cloud cover in the winter and sharp clearness in the summer with low sun angles and long sunsets, can be a great inspiration to architects and artists but it demands a more careful attention and study than in any other context. During the dark period, electric lighting also plays a significant role in our everyday lives, much more than in any other context since many of us have to live in darkness for a large part of the

Preface

day. Our dependency on electric lighting is apparent when considering energy use figures for electric lighting in buildings.

The first chapter of this book explains the benefits and risks of daylighting. The second chapter covers some key building innovations linked to daylighting through time with a focus on Western architectural history. The third chapter presents the main aspects of the human visual system to consider for satisfying illumination while the fourth chapter addresses the non-visual effects of light, which is a relatively recent topic. In the fifth and sixth chapters, basics of photometry and colour are introduced, which are essential to understand the fundamentals of daylighting, daylight metrics and light measurements presented in Chapters 7 and 11 respectively. Moving beyond the horizontal daylight level paradigm, Chapter 8 introduces notions of daylight quality, while Chapter 9 covers daylighting design strategies for side- and top-lighting.

Finally, electric light sources, light measurements, basics of lighting simulations and post-occupancy evaluations are developed in Chapters 10, 11, 12 and 13.

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ABOUT THE AUTHORS

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Marie-Claude Dubois, MArch, PhD, Associate Professor of Sustainable Architecture, Division of Energy and Building Design, Lund University Marie-Claude Dubois is an expert on sustainable design for White arkitekter (20%) and associate professor (80%) at the Department of Architecture and the Built Environment, Lund University, Sweden. She has previously been associate professor (2003-2010) at Laval University, Canada, and senior researcher (2001–2003) within the Daylight Group of the Danish Building Research Institute after completing a PhD at the Faculty of Engineering of Lund University (2001). She has contributed to more than 100 scientific communications in the field of daylighting, building simulation, energy and climatic design. She has previously been Subtask leader of International Energy Agency Task 50 and Task 41.

Niko Gentile, MSc, PhD, Senior researcher, Division of Energy and Building Design, Lund University Niko Gentile is a researcher and teacher at the Department of Archi­ tecture and the Built Environment, Lund University, Sweden. In the past six years, he has been working in the field of lighting and daylighting, mixing technical and observation-based evaluations. In 2017, he defended his PhD dissertation on lighting control systems for energy saving and user acceptance. He participated in the International Energy Agency (IEA) SHC Task 50 and is Subtask leader of IEA SHC Task 61 / EBC Annex 77 ‘Integrated Solutions for Daylighting and Electric Lighting: From component to user centered system efficiency’.

Thorbjörn Laike, MSc Psychology, PhD, Professor of Environmental Psychology, Lund University Thorbjörn’s research interest is in the field of human experience of the physical environment, with a special focus on the light environment. He has been project leader for several multidisciplinary research projects where the non-visual effects of light have been the main interest. He is

About the Authors

also engaged in supervision of doctoral students as well as education at the department of Architecture and the Built Environment. Another of Thorbjörn’s interests is to reach the public with his research results and he gives a large number of public lectures each year.

Iason Bournas, MArch, MSc, PhD Cand, Division of Energy and Building Design, Lund University Iason Bournas is currently pursuing his doctorate degree in architecture from Lund University, Sweden. Since 2016, his research has focused on daylight performance of residential spaces in Sweden and the implications of urban densification. He has authored scientific articles in the fields of daylighting and building performance simulation. His work has been recognized with various awards, among them the Simulation Award at the IBPSA Nordic 2017 conference. He previously earned his MSc degree from the Division of Energy and Building Design at Lund University, Sweden in 2016. He originally studied architecture at the National Technical University of Athens in Greece, where he worked for five years as an architect.

Malin Alenius, MArch, MSc, PhD Cand, Architect and lighting specialist, White arkitekter Malin Alenius is an architect and lighting specialist at White arkitekter and a PhD candidate in Architecture at the KTH Royal Institute of Technology in Stockholm, Sweden. Her research focuses on nonmeasurable qualities of daylight in architecture, with a special interest in methods and tools for architects to work with daylight as an integrated part of the design process.

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CHAPTER 1

Introduction MARIE-CL AUDE DUBOIS

‘Light is where we locate magic in architecture.‘ ANN MARIE BORYS, 20 041

‘Nowadays I don’t regard architecture as a building in itself; it is a means of revealing something else. For me, light is the most ecstatic architectural experience there is, and in many ways the best architecture is a preparation for the experience of light.’

JUH A NI PA L L A SM A A 2

THIS CHAPTER INTRODUCES THE FOLLOWING KEY TERMS AND CONCEPTS:

Daylight, electric light, sunlight, importance of daylight, spectral composition, variability, preference for daylight, daylight and health, daylight and productivity, shortwavelength light, circadian cycle, good daylighting, visual performance, blackbody, infrared radiation, vitamine D, seasonal affective disorder (SAD), benefits and risks of daylighting, luminous efficacy, flicker, visual and non-visual flicker, glare, daylight utilization, contrast, discomfort glare

1 Introduction

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1.1 Importance

of light and daylight

Light is important to people’s health and wellbeing. It significantly affects the mood, emotion and mental state of humans3. The two main sources of illumination in buildings are daylight and electric light, which are both addressed in this book. However, as expressed so rightly by Van Bommel (2009)4, ‘using lighting in the right way in buildings means principally starting by studying the possibility of daylight use’. The authors of this book agree with this statement and therefore, the topic of daylighting is addressed first followed by some chapters on electric lighting. Electric lighting should always be considered as a complement to daylighting.

In contrast to illumination from electric light sources, daylight varies in level and spectral composition with time and therefore provides an interesting variability in building interiors5. The dynamic changes in daylight ‘have positive influences on mood and stimulation’ 6, which has a positive effect on the activation state of people, particularly in indoor work environments7. The changing character of daylight and sunlight thus provides an interior space with ‘a dynamic quality not easily achievable with an electric illuminant’ 8. Daylight illumination levels in a space are ‘dynamic, constantly changing both in intensity and spatial distribution pattern as the two variable sources of daylight – the sun and the sky – interact with the geometry and physical properties of the space, the exterior context and interior conditions’ 9.

In the Nordic countries, the availability and character of daylight exhibits great variability from summer to winter. Daylight variability is particularly extreme at higher latitudes. Above the circumsolar polar circle, the sun hardly rises above the horizon for two months of the year around the winter solstice while in the summer; one can easily walk in a dense forest under the midnight sun. Even under the skies of Skåne in southern Sweden, the gloom is intense during the winter months as the overcast sky is predominant and a thick layer of clouds appears to float not far from the ground. Many days are foggy, and the sun shows up only a few hours each month. The absence of snow as a natural light reflector makes the winter gloom even worse than in Northern Scandinavia, where the snow cover somewhat compensates for low exterior daylight levels. These dark winter skies create very difficult psychological and physiological conditions for the population living at high latitudes. Low levels of vitamine D are predominant in the population and winter depression and the so-called Seasonal Affective Disorder (SAD) affect many people. In the summer, the general mood and atmosphere change dramatically as people can enjoy abundant

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1 Introduction

daylight and sunlight, both before and after work each day. It is not a coincidence that Midsommar (Midsummer) is such a strong tradition in Nordic countries as it falls around the longest day of the year.

Daylight is ‘one way to provide healthy lighting in buildings; it is energy-efficient, rich in short-wavelength light, and available much of the time at high intensities’ 10. Designing buildings that make greater use of daylight and recognize the additional benefits of natural light could have great benefits for the occupants because solar radiation is naturally rich in the short wavelength (blue) radiation that regulates the circadian system11.

In addition, it is worth noting that in non-residential buildings, daylight availability coincides with normal work hours and therefore could displace a considerable part of the energy consumption for electric lighting 12 . Previous research has indicated that ‘standard daylighting techniques can provide illumination which is three to 20 times cheaper than electric lighting with best performance reached by daylight through roof apertures’ 13.

1.2 Definition

of good daylighting

Good daylighting has been defined as ‘the conscious usage of glare-free natural light to illuminate a building’s interior’ 14. There is probably a general acceptance that ‘a space with good daylighting is one that minimizes visual discomfort and provides high levels of visual quality under solely or predominantly daylight conditions frequently throughout the year’ 15. More recently, Reinhart and Wienold (2011)16 proposed a definition of (good) daylighting, i.e. a ‘space that is primarily lit with natural light and that combines high occupant satisfaction with the visual and thermal environment with low overall energy use for lighting, heating and cooling’. These authors added that daylighting design thus becomes a compromise between optimizing the annual daylight availability within a space while making sure that the space is energy-efficient and provides high occupant satisfaction.

1.3 Preference

for daylight

Daylight is invariably promoted as a ‘good thing’, and the literature contains abundant articles in support of the intent to provide ‘good daylight’ for buildings17. Several studies have emphasized the importance of daylight and windows and the numerous positive effects of daylighting on building occupants have been demonstrated by research.

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In work environments, it is generally admitted that daylight is preferred to electric lighting18. Boubekri (1995)19 found that satisfaction with the lighting of workers occupying stations near windows was significantly higher than of work stations located in the core areas, which may also be due to access to a view. Roche, Dewey & Littlefair (2000)20 claimed that people expect good natural lighting in their working places. Escuyer & Fontoynont (2001)21 found that 44 percent of the respondents in a French working environment reported that ‘having plenty of daylight’ was one very important characteristic of their office.

Galasiu & Veitch (2006)22 found a consistent strong preference for daylight when they made a review of 60 peer-reviewed research studies of subjective issues linked to the use of daylighting in office buildings.

Even in residential buildings, recent research indicates that daylight is preferred to electric lighting. A recent survey 23 to inhabitants of a multi-family residential building in Malmö, Sweden indicated a strong preference for daylight in the dwellings.

Bluish morning light has biologically an activating (alerting) effect, while the red sky that we see more often in the early evening has a relaxing effect. In a work environment, both activating and relaxing moments are required 24. In Sweden, the Swedish Work Environment Authority25 states that ‘in areas with continuous working stations, in work rooms and in personnel rooms where people are supposed to stay continuously, there should normally be a satisfying amount of daylight and the possibility for a visual contact with the outside’. One European standard26 stated that daylight may provide all or part of the lighting for visual tasks and windows may provide visual contact with the outside world, which is preferred by most people. A Swedish professor27 even recommended working within two meters from the windows to avoid health related effects of long-time exposure to electric lighting.

1.4 Benefits

of daylighting

Generally, research has demonstrated the benefits of daylight and sunlight for the health and well-being of building inhabitants, including its necessity for the regulation of circadian rhythms28. The most obvious benefits of daylighting in buildings are listed below and further discussed in the following sections: 1. better visual performance,

2. stimulation of the circadian cycle (night/day),

3. reduction of stress, feeling of security and connection,

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1 Introduction

4. increased productivity (relevant for workplaces and schools),

5. flicker-free,

6. high luminous efficacy (lumens/Watts) resulting in energy

savings, 7. improved architectural quality and improved space perception, 8. improved image of the building (through environmental certification), 9. higher building and rental value, 10. positive effect on sales.

The first obvious benefit of daylight is its ability to provide a continuous spectrum of light, which provides a high level of visual performance.

Daylight thus allows a natural representation of colours in the world as seen by the human eye. This is not strange since humans have evolved under the influence of daylight and the light–dark cycle29. Electric lighting is a relatively recent invention. As expressed by Baker (2000)30, ‘fifteen generations ago, a period of little consequence in evolutionary terms, most of our ancestors would spend the majority of their waking hours outdoors, and buildings would primarily provide only shelter and security during the hours of darkness’. A continuous spectrum is one in which energy is present in each portion of the spectrum, as shown in Figure 1.1, which means that all subtle colour shifts can be seen by the eye. This is also probably why people tolerate much lower illuminance levels of daylight than electric light, particularly in diminishing daylight conditions at the end of the day31. Note that fire and tungsten incandescent and halogen lamps (blackbody radiators) also have a continuous light spectrum but their radiation is mostly in the red and infrared portions, see Figure 1.1.

The second benefit of daylight is its capacity to adequately stimulate the human circadian system, which is the cycle of day and night.

Daylight is sufficiently intense in terms of illumination level to stimulate the state of wakefulness while absence of light or darkness leads to sleep.

Recent research showed that the human circadian system requires high retinal exposures from short-wavelength light to be activated32. Recent research has also demonstrated that good sleep requires exposure to high levels of light (especially daylight rich in short wavelength) during daytime. Daylight also provides a colour spectrum which is coherent with respect to time of day. For example, the reddish evening sky is excellent as a cue to prepare for sleep while the bluish morning light has an activating effect. Hence, daylight provides environmental cues to the human brain through visual and non-visual pathways, telling the

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1 Introduction

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Relative power

1

0.8

DAYLIGHT 0.6

0.4

Figure 1.1 Spectral power distribution of daylight versus incandescent, compact fluorescent, fluorescent and LED light sources.

0.2

0 380

420

460

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Incandescent

500

540 580 Wavelength (nm) Fluorescent

620 LED

660

700

740

Low pressure sodium

brain when it is time to wake up and prepare for activities and when it is time to relax and prepare for sleep.

Thirdly, by providing ideal conditions for the visual system and strong environmental cues to the brain related to timing and activities, daylight provides a reassuring and natural biological environment for humans, which most probably has a mitigating effect on stress. Lam and Ripman (1992)33 speculated that ‘there is a sound, viable approach to the design of the luminous environment − a qualitative approach with universal validity because it is derived from fundamental human needs for visual information which are an inalienable part of man’s biological nature’. Among these fundamental needs, these authors mentioned the need for information about the time and environmental conditions, and about weather as it relates to how one should dress or behave. The same authors also mentioned the need for a connection to nature and the need for relaxation and stimulation of the mind, body and senses. Daylight obviously provides the appropriate conditions meeting these basic human biological needs and in absence of these conditions, one may speculate that humans most probably experience a form of environmental stress.

Other research suggests increasing evidence of direct links between the presence of daylight in working environments and productivity34.

Daylighting research has linked increased comfort and self-reported productivity with window size and proximity, as well as with view out,

Marie-Claude Dubois, MArch, PhD, Associate Professor Lund University; environmental specialist, White arkitekter. Niko Gentile, MSc, PhD, engineer, expert in lighting control systems. Thorbjörn Laike, PhD, Professor in Environmental Psychology, Lund University. Iason Bournas, MArch, MSc, PhD Cand., Architect, digital environmental designer. Malin Alenius, MArch, MSc, PhD Cand, Architect and lighting specialist, White arkitekter.

Daylighting and lighting UNDER A NORDIC SKY After nearly a century when electric lighting has dominated the design of building interiors, a return to the use of daylight as the main ambient light source is motivated by energy, environmental, and health considerations.

Good daylighting of building interiors not only promotes low energy use, it has the potential to (re)connect humans to the natural cycle of day and night, which promotes health and well-being. Light is especially important to people in the Nordic countries because it is scarce for a large part of the year and over-abundant around the summer solstice. The unique character of daylight provided by the Nordic sky – with its weak intensity in the winter and low sun angles in the summer – demands careful study and attention, as it is more precious than in any other location.

The current context of densifying cities makes it increasingly difficult to provide sufficient amounts of daylight in buildings under Nordic sky conditions, especially in winter. Analyses using advanced building simulation programs are often needed to predict daylight levels and adjust the building design accordingly. The relevant building regulations and certification schemes need to be understood in depth if they are to be followed by design practitioners. In addition, state-of-the-art electric lighting technologies such as LEDs and advanced control systems require a good integration with daylighting design. Addressing these issues, this book provides the essential knowledge and background to students and practicing professionals who wish to tackle the challenging endeavor of illuminating buildings under a Nordic sky using daylight as the main ambient light source, supplemented by energy-efficient electric lighting systems.

Art.nr 39919

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