Daylight is a highly cost-effective means of reducing the energy for electrical lighting and cooling. But architectural education often reduces the aspect of daylight to eye-catching effects on facades and scarcely discusses its potential effects - not just on cost, but on health, well-being and energy.
This Light Matters will explore the often unexplored aspects of daylight and introduce key strategies for you to better incorporate daylight into design: from optimizing building orientations to choosing interior surface qualities that achieve the right reflectance. These steps can significantly reduce your investment as well as operating costs. And while these strategies will certainly catch the interest of economically orientated clients, you will soon discover that daylight can do so much more.
More Light Matters with daylight, after the break…
1. Optimize urban design and building orientation
The large scale design for daylight starts with urban planning. Create districts and buildings in a form that people receive daylight as their source of light and heat as well as views where and when they want it. This strategy is of course dependent on the specific climate and location. A careful design of a building height forms the basis for avoiding excessive shading from nearby buildings or from different building wings. The next factor is the orientation of the architecture to maximize exposure, for example a south direction for the northern hemisphere. In addition northern exposure should be optimized for indirect diffuse lighting. Finally, enlarge as much as possible the perimeter footprint in order to maximize the daylight for interior spaces. For harvesting daylight, long and narrow building forms work better; atriums offer additional possibilities.
2. The perfect size, form and glazing treatment for windows
Analyse your climate regarding the four forms of daylight for each façade - including the roof: 1. Direct sun, 2. Indirect sun due to reflection from other buildings, 3. Direct cloudy sky and 4. Indirect cloudy sky, which is reflected on the ground. In the northern hemisphere, the south windows should not be oversized and they need protection against direct sunlight to avoid glare and heat. In contrast, the cool north façades mainly receive diffuse light and require window treatments with low heat losses.
When it comes to the aperture itself, differentiate between daylight and the view to optimize the functions individually: Select a clear window for the upper part to increase daylight penetration and use a tinted glass for glare reduction on the eye level. Don’t underestimate the potential of diffuse light from an overcast sky through windows positioned high on the wall or through toplighting options in the roof.
When you begin the glass selection consult a technical expert to find the right glazing treatments regarding the solar heat gain coefficient, the U-value to avoid heat loss and light transmission for good visibility. Finally, ensure that the thermal break of the window frame construction is effective.
3. Shading for visual comfort and cooling
The intense rays of sunlight are critical for visual and thermal comfort. Therefore block the direct sunlight for workplaces and provide screens for glaring sources like neighbouring glass facades, which reflect the sunlight. In summer daylight could easily lead to overheating in buildings with large glass façades. This results in higher energy consumption for cooling. For that reason shading is essential to control thermal comfort. Take a tree to reduce glare and heat in the summer and let the rays of sunlight warm up your building in the winter when the leaves have fallen. For technical solutions, prefer exterior shading elements, which are much more effective than interior, because they keep the heat directly out of the building. In addition, plan movable shading elements for the daily and seasonal changes and let sensors and control systems help you optimize shading for visual comfort and cooling.
4. Work with bright interior surfaces
Design your interior surfaces with high reflectance to increase the daylight level in the depth of the space. Be careful with shiny and very bright surfaces that could cause glare. Therefore use matte light colours to improve the visual comfort. For a bright room impression, keep away from dark surfaces, especially on the back wall.
5. Move task areas close to windows
Detect functions that would benefit the most from daylight in relation to the time of occupation. Offer workplaces access to daylight and keep service rooms in the core of the building. Make sure that furniture does not block the daylight. You could even provide daylight to corridors by using translucent partition walls.
6. Consider daylight reflector systems
Direct sunlight can be easily reflected onto the ceiling for indirect lighting. Use light surface colours for the reflecting surface and the ceiling. Increase the reflectance in front of the window to make it more effective. If you locate the reflector system above eye-level, you can better avoid glare.
7. Energize your building with solar radiation
Beyond improving the light situation within the building, you could also use the power of the sun for solar water heating and install photovoltaic systems for electric devices. The sun is a cost-free medium to cut down your carbon footprint.
Daylight beyond energy
Despite the focus of this list on energy solutions, using daylight is definitely much more than a strategy to optimize the energy-saving potential of buildings. The sun provides basic information like time and weather and supports visual performance as well as comfort. Daylight triggers our circadian rhythms and contributes thereby to our health and well-being.
Of course one should not forget that an optimized engineering solution is not necessarily an aesthetic one. Often hardware, like add-on shading devices, does not create visual interest points out William Lam, a pioneer in the field of architectural lighting and former teacher at MIT, Harvard and Yale: “Designers should be able to use sunlighting strategies without creating a conspicuous ‘sunlighting building’ look.” Daylight design needs to be planned in the concept stage, as part of an integrated design approach. Consequently it’s well worth spending more time on daylight in architectural education and in the design process in general.
Light matters, a monthly column on light and space, is written by Thomas Schielke. Based in Germany, he is fascinated by architectural lighting, works for the lighting company ERCO, has published numerous articles and co-authored the book „Light Perspectives“. For more information check www.arclighting.de or follow him @arcspaces