Many design professionals have adopted daylight integration strategies within buildings, thanks to the acceptance of sustainable building principles and the recognized benefits to occupants. Building owners are now creating and retrofitting facilities that effectively introduce daylight where the occupants need it most. While bringing more natural light in is encouraging, there is such a thing as too much daylight. The best way to achieve daylight integration is through a balanced approach.
You can introduce natural daylight into a building through a variety of means - each with its own strengths and weaknesses. The most common daylight delivery strategies include side-lighting (vertical glazing), top-lighting (skylights, roof monitors and tubular daylight delivery systems), and directional daylight systems (prismatic or sunlight concentrating systems). Developing a balanced daylighting design will most likely include more than one (or all) of these common delivery strategies.
Balanced daylight design is a selective and methodical approach that delivers more light consistently throughout a space with lower lighting level fluctuations during the day and the seasons. Good daylight design can achieve lighting power reduction from 30 to 65%. To know which strategies will best serve your project, examine how well your space has access to unobstructed exposure to the sky. While daylight levels change constantly, the sky – excluding direct exposure to the sun – provides the most consistent indirect daylight, which is easier to design for.
Gain a better understanding of how daylight may be introduced within your building by performing an assessment of the surrounding built environment. Study how the sun moves across the sky during the day. Evaluate seasonal weather and local climate patterns (cloudiness in winter, etc.). If your region is cloudy majority of the time, your space will receive a lower amount of overall daylight so your strategies may need to be more aggressive.
Daylight quality is a direct product of how light is reflects off surfaces. That’s why both interior and exterior surfaces play such a big role in how we interpret if a space is well lit. Surface color and texture greatly influence how light is distributed throughout a space. Higher reflective surfaces reflect light so the space appears brighter, while darker surfaces absorb more light and may make a space seem poorly lit.
Strategically locate higher reflective surfaces within a room to best enhance daylight distribution. For example, vertical surfaces adjacent to a window typically should be lighter in color so the eye is capable of adjusting between the lighting levels coming through the window and other surfaces. Typically the first 15 feet of the wall surfaces perpendicular to the side lighting or top lighting glazing surface should be light colored. Be mindful that lighter colored flooring or polished surfaces, such as marble, may cause unwanted glare problems due to the mirror-like surface. Try to find wall finishes with reflectance values of 55% or higher. Keep in mind that wood surfaces, even ash and pine, will have reflectance below 50% and will get darker as the wood patinas over time.
Proper daylight harvesting can reduce the need for electrically supplied lighting during daytime periods, which will also reduce a space’s cooling demand. However, you need to select the right strategy to realize those interactive savings. For instance, a new skylight may bring in more light in, but if the location and size are not chosen properly, then the skylight may be a source of unwanted heat gain in summer and heat loss in winter. Factor in all of the effects your daylight strategy will have on the performance of your HVAC system when determining the overall savings of that strategy. In existing facilities, the introduction of additional daylighting strategies may put unwanted burdens on existing HVAC systems, causing higher energy and maintenance costs.
When installing a daylight system, consider how the strategy can satisfy multiple purposes and positively influence building performance. Leverage your capital investment so that the daylight system will also accomplish another energy or comfort-related measure. One example is to design the skylight or roof monitor with operable windows to encourage passive exhausting and/or the introduction of natural ventilation.
Allowing daylight into your building is just one of part of the solution. Another aspect is how to control and manage the daylight so it doesn’t cause glare or visual discomfort. You can incorporate fixed controls, such as an exterior shading device or an interior lighting shelf, to shade unwanted direct sunlight penetration from entering through vertical glazed fenestrations. Other controls, like retractable blinds and shade clothes, electro-chromatic glazing, etc., can be activated automatically or through occupant input. Due to human nature, however, occupants that lower shades or close blinds to block out glare often forget to raise them again, which essentially undermines your daylight strategy and negates any electrical lighting savings.
Effective daylighting can enhance a building’s spatial qualities; reduce the load on electric-supplied lighting; and provide significant occupant benefits, such as increased productivity, better employee retention and increased retail sales. As you retrofit your space or work with a design team to build a new one, seek out opportunities to incorporate daylight and gain the benefits in energy reduction and occupant satisfaction.
Eric McDaniel, Associate AIA, LEED AP, is a Technical Consultant at Green Building Services Inc.He specializes in energy and daylight modeling, simulation and analysis for clients throughout the U.S. He can be reached at 866-743-4277 or [email protected].