Daylighting for Laboratories
Julia C. Neville, LC, LEED AP, Newcomb & Boyd
Daylighting is one of the most practical options for conserving energy in laboratories. Reducing a laboratory's lighting power density (LPD) has a positive impact on building HVAC loads, as well.
Laboratories frequently have a minimum average lighting requirement of 100 footcandles (fc) on work surfaces. Reconciling luminance requirements with energy usage limitations and LEED® criteria can prove a formidable task. An appropriate use of daylighting will reduce the need for artificial light, without increasing cooling or heating loads. There are many daylighting considerations to review throughout the laboratory design process, including:
1. Building fenestration and orientation, with regard to excess solar gain and glare. Since daylight will only penetrate approximately 1.5 times the window height, windows must be properly sized and specified to strike a balance between visible light transmittance and solar gain—maximizing the former, while minimizing the latter. These designer-selected variables change, based on building location and orientation, window configuration and whether or not additional structures, such as light shelves are used to reflect or "bounce" light deeper into a space. North facing windows provide for the most consistent amount of indirect daylight and while easterly, southerly, and westerly fenestrations are more challenging, they can be an integral part of a daylighting design, when due consideration is paid solar gain and room size. It is particularly important to remember that solar gain increases with window size. It is equally important to consider the benefits of light and views—the human factor.
2. Controls. In new laboratory facilities, controls are at the heart of energy management. This usually means dimmable fluorescent ballasts communicating with daylight sensors (photocells) through a back-of-house control "brain." To be effective without being distracting, a gradual dimming sequence that ignores passing clouds is desirable. Otherwise, a partly cloudy day may be very distracting for workers and occupants.
3. Energy usage. The ANSI/ASHRAE/IESNA Standard 90.1-2004 allows for l.4 watts per square foot (w/sf), which is ample for most daylighting schemes. For day lit or non-day lit facilities where required light levels are higher than recommendations by the IESNA, providing task lighting via individually switched luminaires can be a way of reducing the LPD.
Julia C. Neville, LC, LEED AP, is an Associate with Newcomb & Boyd in Atlanta, Georgia and specializes in lighting design for educational, commercial, and institutional facilities.
Julia graduated from the University of Alabama at Tuscaloosa, where she received a Bachelor of Science degree in interior design. Prior to joining Newcomb & Boyd in 2005, she worked as a lighting designer with David A. Mintz, Inc., New York, New York; Oxford Lighting Consultants, Oxford, Mississippi; and with Gewin Tucker and Associates, a lighting sales agency in Birmingham, Alabama. She was named an Associate of the firm in 2007. Ms. Neville co-authored the article "Green Security: Working Together," which was published in the September 2007 edition of American School & University magazine. In addition, she has presented on the topics of lighting sources and lighting design to groups such as IESNA and architectural firms.
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