Interest in daylighting and lighting design has never been higher since physiologists discovered a new type of cell in the human eye in 2001. These cells send information about light intensity to the brain centres responsible for controlling circadian rhythms to patterns of light and dark. This tells our bodies when to sleep (“It’s dark!”) and when to awaken (“It’s light!).

This discovery and related research led the Commission Internationale de l’Eclairage (CIE) in 2004 to create five principles of healthy lighting. The principles interpreted the evidence to conclude that people living in industrialized countries receive both too little light by day and too much light by night for optimal well-being. One solution to this problem, the CIE suggested, was a renewed emphasis on architectural daylighting. Daylight is rich in the blue-green area of the visible spectrum (to which the newly-discovered cells are most sensitive) and bright at the times of day that seem most important to regulating circadian rhythms.

The rapid growth in knowledge has spurred the lighting industry and regulatory communities to develop novel lighting and daylighting products and to propose new standards and guidelines. Despite some excellent progress, industry still lacks impartial information to support their innovations and designs.

The VELUX Group recently commissioned NRC Construction to review the literature since the CIE report, this time focusing on the effects of daylight in residences. The conclusions may be broadly summarized as:

• Human well-being relies on regular exposure to light and dark each day.

• Daylight is the most energy-efficient means to deliver the light exposure.

• Uncontrolled daylight also can cause problems; glare from the sun reduces visibility and causes visual and thermal discomfort.

• The optimal pattern of light and dark exposure—as well as the limits at which daylight control is needed—varies by race, age, and individual differences.

• The desire for daylight also depends on how building openings affect the appearance of the space, on the function of the space, and on cultural norms about privacy, enclosure and view.

• A view of the outdoors is also a contributor to well-being, particularly if it is a nature scene or similar pleasing sight (Figure 1). Windowless spaces create monotonous conditions that may be stressful.

• Using daylight is sustainable only when balanced against the effects of windows and skylights on the building envelope, ventilation, and overall energy balance (Figure 2).

The NRC review includes the development of a detailed research agenda showing the information gaps impeding industry advances. Three research priorities were suggested:

• Establish the optimal daily pattern of light and dark exposures for good mental and physical health.

• Determine how our homes can help us to live in the healthy pattern of light and dark, taking into account the way we use windows and shading to control privacy, glare and temperature, as well as light exposures and view.

• Develop design solutions and technologies for different climates that deliver healthy light, warmth, view, and fresh air, with a minimum of energy use.

The results of this review, together with industry consultations, are guiding new research activities at NRC.

Jennifer A. Veitch, PhD, is best known for her research on lighting quality, individual controls, and environmental and job satisfaction in open-plan offices. Dr. Veitch is a Principal Research Officer at the National Research Council of Canada, where she has led research into lighting effects on health and behaviour for over 20 years. She is a Fellow of the Canadian Psychological Association, the American Psychological Association, and the Illuminating Engineering Society of North America. In 2011 she received the Waldram Gold Pin for Applied Illuminating Engineering from the International Commission on Illumination (CIE). She serves CIE as Director of its Division 3, Interior Environment and Lighting Design.

Executive Summary: The IESD were commissioned by the VELUX Group to carry out a parametric climate-based daylight analysis for two residential building types with various window congurations and external obstructions. Each of the ten building congurations was evaluated for all combinations of eight orientations and six climate zones. Thus there were 480 sets of unique climate-based daylight simulations. The evaluation was founded on the useful daylight illuminance (UDI) scheme which determines the occurrence of absolute levels of illumination within four ranges: less than 100 lux; 100 to 500 lux, 500 to 2,500 lux; and, over 2,500 lux. The limits of these ranges are founded on human factors data from occupant surveys. The key indicator for “good” daylighting is the degree of occurrence of illuminances in the range 500 to 2,500 lux (labelled the UDI-a metric) since this range: provides adequate illumination for the majority of tasks; is associated with a very low probability for the switching-on of electric lights; and, the higher values in this range are now believed to have benecial eects for both productivity and long-term health. This study has shown that the addition of skylights invariably improves the overall daylighting performance of the space. For some designs, the addition of skylights led to a typical increase in the occurrence of the key UDI-a metric from 12% to 45% of the occupied period of the year (i.e. 08h00 to 20h00).

John Mardaljevic (PhD, FSLL) is Professor of Building Daylight Modelling at the School of Civil & Building Engineering, Loughborough University. Mardaljevic pioneered what is now known as Climate-Based Daylight Modelling (CBDM- http://climate-based-daylighting.com). Founded on rigorous validation work, CBDM is now the basis for research and, increasingly, industry practice worldwide. Mardaljevic’s practice-based research and consultancy includes major projects such as the New York Times Building and The Hermitage (St. Petersburg). He currently serves as the ‘UK Principal Expert on Daylight’ for the European Committee for Standardisation CEN / TC 169 WG11, and on a number of International Commission on Illumination (CIE) technical committees. In 2012 Mardaljevic was presented the annual UK lighting award by the Society for Light and Lighting (SLL). He is CIE-UK Representative for Division 3 (Interior Environment).

The study uses a domestic dwelling as the setting to investigate and explore the applicability of daylighting metrics for residential buildings. The metrics address daylight provision for task and electric lighting usage. In addition to these it also investigates the formulation of preliminary metrics to evaluating the potential for non-visual eects. The setting, a residential building with and without skylights, was evaluated for all 32 combinations of eight European climates and four building orientations covering the cities of Hamburg, London, Madrid, Moscow, Ostersund, Paris, Rome and Warsaw. The evaluation is based on a real life renovation case in which new skylights have been added to the kitchen, living room, large and small bathrooms and staircase.

John Mardaljevic (PhD, FSLL) is Professor of Building Daylight Modelling at the School of Civil & Building Engineering, Loughborough University. Mardaljevic pioneered what is now known as Climate-Based Daylight Modelling (CBDM- http://climate-based-daylighting.com). Founded on rigorous validation work, CBDM is now the basis for research and, increasingly, industry practice worldwide. Mardaljevic’s practice-based research and consultancy includes major projects such as the New York Times Building and The Hermitage (St. Petersburg). He currently serves as the ‘UK Principal Expert on Daylight’ for the European Committee for Standardisation CEN / TC 169 WG11, and on a number of International Commission on Illumination (CIE) technical committees. In 2012 Mardaljevic was presented the annual UK lighting award by the Society for Light and Lighting (SLL). He is CIE-UK Representative for Division 3 (Interior Environment).

A look at three new daylight modelling techniques developed at the Institute of Energy and Sustainable Development, De Montfort University, Leicester, UK.

The modelling of illumination and of solar access/penetration are carried out using very different approaches. Daylight illumination is invariably assessed using the daylight factor method under standard overcast sky conditions. Solar access/penetration is typically evaluated using a series of images showing the pattern of direct sun illumination for certain times of the day or year. Both approaches, each over half a century old, were originally carried out using scale model techniques: in an artificial sky for daylight factors or with a heliodon for solar access/penetration. Although different, they share a common trait: at best they each give only a limited insight into the phenomena they are intended to characterize.

Consider first the daylight factor approach. It is readily apparent that illumination under standard overcast sky conditions presents a special case scenario: even in England we see the sun now and then. Northern European climates approximate to the standard overcast sky model for less than 50% of the actually occurring sky conditions. For sunnier climates the approximation is even less valid. For solar access/penetration, the images show only patterns of illumination relating to the sun position. They can indicate only when illumination of a surface may occur, but it is impossible to quantify the degree of illumination or its occurrence throughout the year.

More recently, computer simulation techniques have been successfully applied to both approaches. Daylight factors can be predicted using lighting simulation programs that accurately model inter-reflection, e.g. Radiance. Often the same simulation program can be used to render a sequence of images showing the patterns of direct solar illumination inside and on the facades of buildings. Although computer simulation may offer advantages over scale modelling, the fundamental limitations of the basic approach in each case remains.

Over the past five years, research in lighting simulation at the IESD has focused on developing a set of three simulation-based techniques that each offer a significant advance over the traditional approach. Outline descriptions of each are presented in this paper.

John Mardaljevic (PhD, FSLL) is Professor of Building Daylight Modelling at the School of Civil & Building Engineering, Loughborough University. Mardaljevic pioneered what is now known as Climate-Based Daylight Modelling (CBDM- http://climate-based-daylighting.com). Founded on rigorous validation work, CBDM is now the basis for research and, increasingly, industry practice worldwide. Mardaljevic’s practice-based research and consultancy includes major projects such as the New York Times Building and The Hermitage (St. Petersburg). He currently serves as the ‘UK Principal Expert on Daylight’ for the European Committee for Standardisation CEN / TC 169 WG11, and on a number of International Commission on Illumination (CIE) technical committees. In 2012 Mardaljevic was presented the annual UK lighting award by the Society for Light and Lighting (SLL). He is CIE-UK Representative for Division 3 (Interior Environment).

This project studied 13 Danish families in various homes and from various age groups, all residents on the island of Zealand (in both towns and the provinces). A total of 24 respondents were involved. The theme was what the window means to them, how they use it in daily life, and what they value and do not value about it. Analysis has revealed the general understanding of the ‘good window’. The report thus puts words and pictures to what the window means to ordinary people and gives new insight into the value of the window. It is important to stress that the window is far more than a purely functional tool only used to air out the home. The analysis found six themes that all describe what the window signifies to people – and what they do with it.

1. Daylight and kinds of light

2. View out and view in

3. Following the sun

4. The staging properties of the window: window frames, curtains and decoration

5. The role of the window in social life: absence and closeness

6. Safety and functionality

All themes were present for all informants, though 1, 2, 4 and 6 particularly so.

Bettina Hauge, DTU (Technical University of Denmark), MSc (anthropology), PhD (sociology), HD(A). For more information, please feel free to contact me at DTU, Management Engineering, Design & Innovation, behau@dtu.dk.

This research project has investigated 17 households in Germany (cities and rural areas). The main aim was to learn about the significance of the window to these people: What they think of their windows, how, when and why they use them in their everyday life, if they have a favorite window and why, as well as the opposite. The report also includes a special focus on overheating and people’s strategies against this. Knowing about what people appreciate in a window and their actual practices and the reasons for their behaviour may be useful in many different ways, for instance to inform public strategies for overheating or to communicate with people in a more user informed way.

The people participating in the study lived in different houses and had different backgrounds. They were involved in the project over a period of 3-4 months. The prolonged participation was facilitated through a variety of ethnographic tools that required their involvement, such as making a diary of their heating experiences during a random week in the summer of 2014, taking photos of windows and sending postcards with specific tasks.

Bettina Hauge, DTU (Technical University of Denmark), MSc (anthropology), PhD (sociology), HD(A). For more information, please feel free to contact me at DTU, Management Engineering, Design & Innovation, behau@dtu.dk.

This report presents the results of simulations of daylight conditions in three rooms with three different window configurations:

– an ordinary, vertical window,
– a dormer window, and
– a roof window.

The simulations were performed with the Radiance Lighting Simulation System (Ward Larson & Shakespeare, 1998) included in the AutoCAD Desktop program. The aim of this project was to compare daylight conditions in three rooms under overcast sky conditions and under sunny sky conditions at two different times of the day (12:00 and 15:00). These simulation times are a minimum set to represent daylight conditions in the rooms. The three rooms studied had identical floor area and floor to ceiling height and orientation (south). They also had identical glazings (area and glass combination), glazing height and identical wall, floor, and ceiling reflectances.

Impact of three window configurations on daylight conditions, Phase 2

This report presents the results of simulations of daylight conditions in three rooms with three different window configurations:

– a vertical window,
– a dormer window and
– a roof window.

The simulations were performed using the original UNIX-based Radiance Lighting Simulation System (Ward Larson & Shakespeare, 1998) as well as a Windows version included in the AutoCAD Desktop program. The aim of this project was to compare daylight conditions in three rooms under overcast, intermediate, and sunny sky conditions for different orientations at different months and times of the day. The three rooms studied had similar floor area and floor to ceiling height. They also had identical glazings (area and glass combination), glazing height and identical wall, floor, and ceiling reflectances. In order to establish a method for the assessment of daylight quality in a room, a number of daylight parameters were investigated:

– Horizontal illuminance and daylight factor
– Cylindrical illuminance, centre of room, horizontal and vertical plan
– Illuminance on cube, centre of room
– Vertical-to-horizontal illuminance
– Luminance distribution
– Luminance ratios, perspective view towards window
– Average luminance in the field of view, 40° band
– Daylight Glare Index (DGI)
– Luminance Difference Index (LD index)
– Scale of shadow

In addition, the need for using a solar shading device for each of the three windows was assessed over a whole year under typical weather conditions as defined in the Danish Design Reference Year (DRY). Finally, the differences in lighting conditions when using a 3-layer glazing unit with 2 low-e coatings, instead of a typical 2-layer low energy glazing with 1 low-e coating, were examined.

A strong focus on lighting quality and productivity as well as a renewed interest in energy efficiency in recent years has highlighted the lack of appropriate design guidance for architects, interior and lighting designers for creating glare-free daylit work environments, especially for offices. Well-developed design guidelines based on visual experience and careful monitoring of the design process from the start would likely go a long way in ensuring that daylit work environments are essentially glare-free. Extensive research on human vision and perception and innovation in architectural lighting design practice and technology have produced considerable opportunities for compiling a document aimed at providing useful design assistance for creating healthy and enjoyable work spaces. Work on a design guide is currently under way as part of the activities of the CIE Division 3 Technical Committee 3-39: Discomfort Glare from Daylight. It begins with the human visual senses and key parameters for describing and assessing visual environments. This paper outlines the approach taken and highlights the essential aspects considered.

Werner Osterhaus, Architect, Head of Lighting Design Research Laboratory, Department of Engineering, Aarhus University.

Daylight, rather a fact than a matter of discussion for many millennia, has lost its dominant role in architecture during the years 1950 till 1965. The artificial lighting of interiors had reached its long promised goal and was considered superior to daylighting in quality. In many countries, office buildings and even schools were built without windows because the new techniques of lighting and air conditioning were believed to perform much better than conventional lighting from windows and skylights and air supply through wall openings. Studies of the ERGONOMIC Institute, Berlin, in German office buildings, published first in 1990, revealed that almost 60 % of the workers considered lighting a health hazard, and, in addition, that in work spaces where artificial lighting dominates the self-reported state of health of workers was far below of those working in areas with daylight dominance. Since this was not only true for „vision-related“ symptoms like eye fatigue, but also with other health complaints related to temperatures or noise we assumed that the effects are likely to be caused by influences of lighting on the hormonal system. During the 1990s, a series of studies on the impact of lighting on humans were performed in the USA. They included offices, schools and retail buildings. The outcome in short is, that daylight was demonstrated to improve human performance, to change the state of health for the better, to help boosting sales in retail shops. In addition, other studies have demonstrated its impact on the energy efficiency of buildings.

Ahmet E. Çakir, ERGONOMIC Institut, Berlin.

Much focus on sustainable buildings has been on energy aspects. However, health is the most precious resource we have, and energy is only one aspect of sustainability. A primary goal for sustainability should be to sustain good health and a healthy living environment. This was the starting point for a series of workshops with international experts initiated by the VELUX Group, based on a wish to start a discussion on how to create healthier homes.

This document describes a comprehensive vision to realize healthy homes that support the different biological needs of their occupants, in particular including their circadian rhythms and sleep-wake cycles. It is based on discussions and findings of 5 workshops; ´Light and circadian rhythms´ (WS 1), ´Indoor climate´ (WS 2), ´The historical perspective´ (WS 3), ´ What to monitor and how´ (WS 4) and ´How to wrap-up the specifications´ (WS 5). The workshops were carried out by scientists and consultants specialized in healthy buildings, indoor environment, architecture and planning from November 2012 to August 2013.

Today, most residential buildings are designed or renovated in order to achieve a better energy performance. We acknowledge that there is an urgent need to transform our building stock to a better energy performance level, e.g. by increasing thermal insulation, installing better energy performing windows and improving energy efficiency of heating, cooling and ventilation systems. On the other hand, improving the energy performance of buildings should not result in a negative impact on health, wellbeing and comfort of building occupants. A successful design or redesign of a residential building should aim at the best health and comfort performance in addition to good energy performance. It is important to remember that dwellings are primarily meant to provide a safe and enjoyable living environment for their inhabitants. In that context, it is also important to consider that the primary purpose of Building Regulations is to provide for the health, safety and welfare of people in and around buildings.

The principles and guidelines in this document can be used to guide and improve the design of residential buildings of all types, including apartment buildings, and are applicable to both new and existing dwellings.