Daylighting 101

by Joel Loveland and the New Buildings Institute

The following information presents a quick overview of the basics of daylighting design. It is not intended to cover all the design issues, but instead to highlight some of the key ones.

A good daylighting design
What do we mean by daylight? Inside a building, daylight performs the same way as diffuse light from the overcast sky. Good daylight is soft and cool, both in temperature and color. If a building owner or an architect sets daylighting as a design goal, the building will admit this diffuse light, proportioned to the needs of the people in its spaces.

Diffuse Daylight not sunlight
Sunlight -- the direct rays of the sun -- may be welcome on a day at beach, but not inside offices and classrooms. Architects want to avoid generously opening a building to the sky in ways that give access to the sun's direct rays. Glare and overheating from the sun's rays are debilitating in areas where workers perform critical visual tasks. In offices, and classrooms, direct rays seriously distract from the work at hand.

Instead, architects seek to maximize the penetration of diffuse light and block the direct sunlight. The U.S. Green Building Council's LEED™ standard requires that no direct sunlight be admitted to critical task areas in order to be considered as daylit.

The many different climates of the Northwest produce a wide diversity of sky conditions and therefore daylighting design challenges. Every area of the region has great potential for using daylight. Even the dark and gray overcast of the coastal Cascadian region of the Northwest offers abundant diffuse light, an ideal condition for daylighting design.

Daylight varies by season and time of day During the day, daylight changes in both direction and intensity. A good daylighting design is one where the patterns of light and the patterns of work follow the movement of light in the sky. A building that uses daylight effectively also accounts for changes in seasonal cycles.

Building shape and orientation
Buildings can be shaped, however, to take maximum advantage of sunlight's benefits. Rays of sunlight are directional, warmer of both temperature and color than daylight, and piercing and strong. Architects create designs that enable sunlight to give shape to a building at the same time they control its direct penetration into areas where critical visual tasks are performed.

Sunlight from the sun's relatively horizontal movement across the southern sky is reasonably simple to control. Spaces illuminated with diffuse southern sunlight change on a seasonal basis and are adaptable to critical visual tasks. However, spaces illuminated by the rays of eastern and western sunlight radically change on a daily, hour-by-hour basis and are extremely difficult to adapt to critical visual task environments.

Buildings which set daylighting as a high priority will begin to take on particular shapes. A building that is well daylit will most probably become thinner and with less surface. It will feature less window area to the low and glaring sunlight of the east and west, while opening its windows to the bright zenith of the overcast sky and to the controllable sunlight of the southern and northern sky. The form comes from the intrinsic difficulty of conveying the soft gray-blue light of the zenith deeply into a building -- most probably from a vertical window with a limited view of the brightest upper portion of the sky vault.

An example is the Emerald Public Utilities District building in Eugene. The building was recognized as a model for daylighting and energy efficiency, winning the AIA's Architecture + Energy (A+E) Award in 1999. Its overall form was shaped by an interest in admitting the diffuse light of the overcast sky, opening itself to the controllable northern and southern sunlight, and minimizing its exposure to the east and west.

The Seattle Port Authority Headquarters at Pier 69 has been recognized as a state-of-the-art daylit office building. Built on the foundation of an existing pier, the two-story open office area is elongated to the east and west with its only windows facing north and south, with a series of northern-sloped roof skylights. The building, quite deep from north to south, opens through the center with an atrium to allow for the penetration of daylight into the deepest recesses of the first floor of office space.

Such design ideas are not entirely new. The Seattle School District's Wilson Elementary School, designed and built in the mid 1950's represents an unpretentious expression of simple daylighting ideas. Planned to maximize the north and south windowed surfaces, each classroom is no further from the window than 26 feet. Clerestory windows wash the interior wall opposite the windows with abundant daylight.

Windows and Skylights
The windows emphasize daylight and refine the view, skylights, light-shelves, clerestories, light wells and other devices.

The most critical visual tasks should take place near controllable daylight from the north or south, the roof, and possibly the west. Rarely should these tasks take place in light from the east unless it is shaded by the building itself or some other vertical element.

Depending on the climate and building type, western orientations can be good surfaces for daylight windows. Roofs can offer excellent daylight opportunities through vertically windowed monitors, sloped clerestories and diffusely glazed skylights.

The window needs to illuminate the walls and ceiling and thus indirectly light the space. Windows should be designed to admit daylight while limiting or controlling sunlight. The building, window and room become integrated as a single light fixture. The window should allow for the penetration of visible light, not heat. Heat from windows is rarely needed in most commercial buildings in the Northwest.

Features such as skylights, clerestories, light-shelves and high, light-colored walls and ceilings bring the light deeper into the building, balancing the brightness of the sky and windows.

Turn off the Lights!
The electric lighting system, most likely a florescent system, should be oriented parallel to the source of daylight. This electric lighting design when integrated with dimming ballasts and daylight-sensing electric light controls and wiring will allow for the electric lights closest to the windows to be dimmed on or off as the daylight becomes more or less available.

Daylighting design process
The most effective daylighting designs ensure that electric lighting is only needed at night and on very cloudy winter days. This does not mean that we can simply add many windows, allowing the penetration of the sun into the building.

How can building designers and owners introduce effective daylighting to their interior spaces? They should:

Start early in the design process with daylighting goal setting. Set specific design goals that acknowledge the value of daylighting in all parts of the building.
Assemble an experienced design team, one skilled in daylighting design and modelling.
Test your design ideas by simulating your proposals with physical models, or possibly on more a limited basis with digital models.

While a high-performance daylighting design need not cost any more than a standard building project, it may require the re-proportioning of the standard capital budget line items. For instance, the reduction of lighting, cooling and or heating loads which correspond to a good daylighting design should release money from the HVAC equipment budget, often 30 percent of the total construction cost of a building. These funds can then be redirected to the building skin and lighting systems.

Some daylighting projects may have slightly higher initial costs for the lighting system and building skin associated with design, lighting controls, and improved window systems. These costs will be offset by decreased air conditioning equipment costs, lower operating costs and finally, significant productivity gains.

Testing the performance of the design
Testing is one of the most important aspects of daylighting design, but until recently, most design teams have not tested daylighting decisions. This has led to a poorly informed decision making process that has produced some very poorly daylit spaces.

Daylighting design proposals are best tested with physical models of the building or space in question. These physical models should be constructed to a scale and detail that is appropriate to the precision of the questions being asked. Smaller scale models with much less detail are excellent tools for testing concepts of daylighting and sun control. These model studies often occur during schematic design and the earliest stages of design development. Larger scale physical models in the range of 3/8 to 3/4 inches to the foot are excellent for testing the more precise questions that are asked during the final stages of design development of construction drawings.

Get help
Daylighting decisions can be explored though the professional staff at the Network of BetterBricks Integrated Design Labs. The services of the Daylighting Advisors are a free resource for Northwest building owners, architects, lighting designers and engineers. Each Lab includes a daylighting laboratory where consulting staff can help design teams develop daylighting schemes, and assist in the production of small-scale physical models, digital models and full-scale mockups.