Integrated Daylighting Systems

This report summarizes an assessment of integrated daylighting systems (IDS) at 13 Federal building sites in California, Nevada, Illinois, Indiana, and Washington, D.C. These Federal buildings were retrofit between 2009 and 2012 as part of the U.S. government’s American Recovery and Reinvestment Act (ARRA). 

Lighting is often the single largest end use in commercial buildings and directly impacts heating and cooling, total energy use and load shape so it is an important focus of GSA’s energy efficiency programs. Windows and their associated external and internal shading systems help “shape” the quantity and quality of daylight and sunlight entering the building, which also varies with climate, site, orientation and other building parameters. “Daylight dimming” as an electric lighting control strategy is implemented via set point tuning – regulating electric lighting output according to target light levels at the work location – and daylight dimming – allowing electric lights to dim dynamically in response to available natural light. As a result, electric lighting supplements daylight when needed, rather than operating at a constant level. The consequence is a reduction in electric lighting operation, which results in energy savings. 

IDS have the potential to save significant energy in the perimeter areas of buildings. This perimeter area is also referred to as the daylit zone, and is defined here as being within the distance of two times the maximum window height from the window wall. Single story spaces can be entirely daylighted with skylights, but were not examined in this study. Other daylighting benefits are more difficult to quantify but include: providing building occupants with a pleasant, dynamic, and more comfortable working environment; and the psychological and physiological benefits associated with a direct connection with views outdoors.