Detail of Mini Optical Light Shelf daylighting system, MOLS 51 Design. Source: Architectural Energy Corporation
Interior view of open office area, with redirected daylight illuminating the ceiling. Photo: Architectural Energy Corporation

Project: Xilinx Development Center, Longmont, CO

Owner: Xilinx Corporation

Architect: Downing Thorpe James (Design Architect)
The Neenan Company ( Architect-of-Record and General Contractor)

Energy, Daylighting and Sustainable Design Consultant: Architectural Energy Corporation

Mechanical/Electrical Engineer: BCER

Automated Shading


Typical Vision WindowsProperties:
Clear insulating low-solar-gain low-E glass

Typical Daylight Window Properties:
Clear insulating high-solar-gain low-E glass

Xilinx Development Center

Effective daylighting requires attention to a myriad of issues, with building orientation and massing, site climate, interior spatial organization, appropriate glazing location and selection, and integration with the electric lighting and HVAC systems among the more important considerations. The Xilinx Development Center is an excellent example of how these factors were addressed by the design team, especially the "details," which often do not receive adequate attention.

The Center houses the software development activities of Xilinx Corporation. It is the first building on Xilinx's new Colorado research campus, and established a design benchmark for architectural, landscape, and sustainable design. Sustainable design concepts incorporated into the Center include indigenous landscaping, underfloor air distribution, direct/indirect evaporative cooling, and low-environmental impact materials.

Campus master planning placed the Development Center in the center of the site on an east-west axis. This building orientation resulted in perimeter open offices on the south and the north, with a core zone of support spaces and common areas, facilitating the use of daylight to provide ambient lighting of the perimeter open office areas.

Exterior view of south fenestration with shading device between the lower "vision" glass and upper "daylighting" glass. Photo: DTJ Design

Within the integrated design approach, perimeter windows were conceived as "vision" glass from 3 to 7 feet above the floor, and "daylight" glass from 7 feet above the floor to the 10-foot ceiling. The vision glass has a relatively low visible light transmission and a low solar heat gain coefficient. The daylight glass has the same U-factor as the vision glass, but a high visible light transmission and a high solar heat gain coefficient.

The high visible light transmission of the daylighting glass provides adequate daylight onto Architectural Energy Corporation's innovative, patented Mini Optical Light Shelf (MOLS) daylighting system, which shades occupants from direct sunlight while redirecting daylight deep into the open office space. Each MOLS unit consists of a frame which supports a series of fixed horizontal reflective louvers, of a unique compound geometry, that redirects daylight uniformly across the ceiling surface. The illuminated ceiling surface provides ambient light to the space below. Photosensors determine the ambient light from daylight and raise or lower the indirect electric lighting to maintain the minimum ambient lighting level.

The excellent daylighting strategies within the overall Xilinx architectural scheme were reinforced through effective window design and glazing selection, integration with the electric lighting design, and implementation of effective shading and lighting control elements, including the MOLS daylighting system.

Interior view of Architectural Energy Corporation's patented Mini Optical Light Shelf daylighting system, MOLS 51 Design. Photo: Architectural Energy Corporation

An important factor in Xilinx's energy efficiency is the lighting approach. Beyond the careful integration of daylighting and electric lighting, the design team employed an ambient, task, accent lighting strategy to provide only the required amount of light:

  • Daylighting and indirect (pendant) electric lighting provide 20–25 fc of ambient illumination, with photosensors raising or lowering electric light levels as required to maintain the minimum ambient light level.
  • Furniture-mounted fluorescent lighting provides task lighting requirements of 40–50 fc with accent lighting highlights on specific areas, such as break rooms and wall-mounted art.

Carmody, J. S. Selkowitz, E. Lee, D. Arasteh, T. Willmert. Window Systems for High-performance Buildings. Norton, 2004.


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