Why Use Daylight?

A model of the library at Sauk Intermediate School, Central School District.

Lighting a space with daylight can make people happier, healthier, more productive; and if you turn the electric lights off, you can also save a great deal of energy. Recent studies, correlating lighting with productivity, show that integrating daylight with electric light in schools, offices and retail stores has a positive impact on a business’ bottom line. As important as being better places to work is, these daylighted high performance buildings offer an increased return on an owner’s investment through the building’s increased overall asset value at no additional total construction cost.

In the United States, access to daylight, views to corridors to the outside and the rejection of glare in the workplace are key components for compliance with the United States Green Building Council’s (USGBC) Leadership in Energy and Environmental Design (LEED1) sustainable green building standards. Daylighting goals such as these are formgivers for architecture and hallmark a new era of high performance and highly productive building designs. They reveal the ecology of a building’s landscape setting and attempt to reconcile its development through sustainable design.

In Europe, countries such as Denmark require employees to have access to daylight in their offices as a matter of health and safety. Most Danish schools have excellent daylit classrooms, less for the students but more from an awareness of how important it is to maintain the most productive and healthful workplace for its teachers.

Increased Productivity: Learning and Retail Sales

The overwhelming results from worker satisfaction, retail sales floor preference and student performance research indicates that people prefer to work, buy and go to school in spaces illuminated with glare-free daylight.

Because occupants feel better in their space, they can concentrate better and longer, which can lead to greater productivity. Many business-oriented periodicals over the last two years have begun to underscore the role of daylighting in the results of recent workplace productivity research. Business Week and Fast Company have both highlighted the role of the built environment in attracting and retaining workers. The financial impact on the economy’s bottom line is substantial considering the fact that when amortizing the 30-year cost of operating a business, where office work is the dominant activity, employee-related costs are generally 15 times the costs associated with building operation and nearly 50 times the capital cost of construction.

A study of three school systems in Washington, Colorado and California found that students in classrooms with the most diffuse and glare-free daylight improved their performance on standardized tests by up to 26 percent over classrooms without daylight, and 10 percent over average classrooms.2 A second peer review of this study confirmed and extended its results in 2001.3

Retailers such as Walmart and Costco have been implementing skylighting strategies for more than a decade. More recently researcher Lisa Heschong took a close look at a single retail grocery chain in California where skylighting was used in 60 percent of the 100 or more stores reviewed. She discovered that the skylighted stores had 40 percent higher sales that were attributable to their use of daylighting. Because of these indicators, single-story high-bay retail store roofs are quickly becoming a sea of skylights.

Energy Savings

The library at Sauk Intermediate School, Independence, Oregon designed by BOORA Architects, utilizes the aforementioned daylighting technologies.

The majority of commercial space in the United States is either one-story or within 25 feet of an exterior wall. This means nearly every commercial building is a potential daylighting project, not only for designing a quality daylighted workplace, but also designing electric lighting systems where the lights are dimmed with the availability of daylight. With fluorescent lighting systems, often 75% of lighting energy consumption can be saved. In a good daylighting design, additional energy savings can be gained by minimizing solar heat gain by carefully designing the windows for controlling the glare of the sun. Many of the daylighting projects that I work on at the BetterBricks Daylighting Lab come into the lab with too much window area relative to a baseline building. By showing designers that daylit buildings don’t require more glazing, but simply the re-proportioning of it related to the availability of daylight and the zoning of the occupants, we are able to make them understand that daylit buildings don’t need to have greater capital costs over other buildings of the same type. Buildings with natural daylight use less energy and are healthier and more productive to work in. Many have smaller refrigeration and heating loads, thus smaller and less expensive HVAC capital costs.

Increased Asset Value

Exterior rendering of the Seattle Justice Center, Seattle, Washington. Design by NBBJ Architects.

Although a high-performance daylighting design should not cost more than a standard building project, it may require some re-proportioning of the standard capital budget lines. For instance, the reduction of lighting, cooling and 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 commercial building). The money can then be put towards the building skin and lighting systems. Thus, some daylighting projects may have slightly higher initial capital lighting system and building skin costs associated with design, lighting controls and improved window systems. These costs will be offset by decreased air conditioning equipment costs, much lower operating costs and finally, significant productivity gains. High performance building features offer an increased return on an owner’s investment, which over the life of the building can enhance its income and increase the overall asset value of the property.

Recent Trends: Better Ideas About Daylight

The west interior of the Seattle Justice Center model with double skin.

By including daylighting as a building design goal, building owners and architects attempt to admit the diffuse light of the sun or overcast sky, proportional to the needs of the people in its workspaces.

Counterposed to generously opening a building to the sky in order to maximize the penetration of diffuse light is the need to diffuse or block direct rays of the sun. Glare and overheating from the sun’s direct rays is debilitating in areas where critical visual tasks are common. In offices, classrooms and other similar spaces, the direct rays of the sun can seriously distract from the work at hand. Studies in elementary school classrooms have shown up to 15 percent decrease in learning when direct sunlight is present. In order for spaces to be considered daylit, The USGBC LEED Standard requires that no direct sunlight be admitted to critical task areas.

So, what is the definition of daylight? Daylight, the diffuse light of the overcast sky, similar in all orientations, bright above and dark at the horizon, is soft and cool of both temperature and color. We think of it as the winter “gloom” in many northern regions of North America. The bluish-gray blanketed overcast sky typifies the Pacific Northwest and the Atlantic Northeast.

Sunlight, as it sounds, is the direct rays of the sun. It is the Colorado desert, the great western basins, the rolling hills of California and even the seasonal short bursts of sunlight associated with the summers of the Pacific Northwest - like tanning at the beach. Rays of sunlight are directional, warmer of both temperature and color, piercing and very strong. Sunlight gives shape to a building through its control of direct penetration into critical visual task areas. The 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. 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. As previously mentioned, studies in classrooms show that learning decreases where sunlight predominates. The different climates of North America produce a variety of sky conditions, which makes daylighting design a challenge. Almost every part of the continental United States is a great region to use daylight. Even the dark and gray overcasts in the northern coastal region offer abundant diffuse light—an ideal condition for daylighting design.

Daylighting design is the use of good design sense, not the application of technology. Daylighting design is the pattern of light in the sky told as a story in the building’s form and details. To save lighting energy, the appropriate electric lighting systems and controls must be designed, installed and commissioned, but the basic “technology” of good daylighting is good design that is well tested in daylighting simulation facilities by the architectural team.

Today’s Advances: Testing Daylighting Projects For Performance

Until most recently, many design teams have not commonly tested daylighting decisions. This has produced spaces that are very poorly daylit. As with most other systems in buildings, a design hypothesis MUST be rigorously tested for its efficacy. Given the constraints of time and materials, daylighting design proposals are generally best tested with physical models of the building or space in question.

The Betterbricks Daylighting Lab in Seattle, Wash., is working on more than 150 projects a year with architects in the Pacific Northwest. The Lab also tests a significant number of the most developed projects with physical models. This represents a huge advance in design team priorities for most architects. Since the Daylighting Lab facility and expertise is easily accessible and comes at little or no cost, hundreds of architects with projects in the Pacific Northwest have demonstrated a high interest in the lab by bringing in projects and design problems. The Northwest Energy Efficiency Alliance funds the BetterBricks Daylighting Labs through a daylighting and commercial building initiative now under the identity of BetterBricks. BetterBricks is a network of information and resources designed to help to meet the real-world needs of Northwest building professionals.

Three to four new projects come into the Daylighting Lab every week. There is a ground swell of daylighting projects occurring in the Pacific Northwest and design teams are testing their daylighting schemes and adjusting their design according to a primary tool—the physical model.

Working closely with the Betterbricks Daylighting Labs, these physical models are carefully designed and constructed to be of a scale and detail that is appropriate to the precision of the questions being asked. Larger scale physical models in the range of 3/8 to 3/4 inches to the foot are excellent for testing the precise questions that are asked during the final stages of design development of contract drawings. Smaller scale models with much less detail are excellent tools for testing general concepts of daylighting and sun control. Most of these model studies occur during schematic design and the earliest stages of design development.

Daylighting Design: How To Make It Happen

Start early in the design process with setting daylighting goals while scoping the project, programming and more generally during pre-design. Set the stage in a request for qualifications (RFQ) that sends the message, “We want a design team that is experienced in daylighting design.”

Assemble an experienced design team. The team should be experienced in the early integration of the building forming aspects of daylighting, electric lighting and HVAC design and testing with the more traditional aspects of building design.

Build your proposals on the patterns of light. Well-planned daylighted buildings happen at schematic design. Their overall form responds to the pattern of the path of the sun to eliminate its penetration and to maximize the distribution of gentle, diffuse daylight from the overcast sky.

Test your design ideas by modestly simulating your earliest proposals with physical models, or possibly on more a limited basis with digital simulation tools. Follow these early assessments with ever more complete simulations of your proposals through design development and contract drawings.

Commission your building upon project completion.