Daylighting is a critical element that influences every design decision. It uses natural light from the sun and sky to illuminate interior spaces. An economically and environmentally responsible lighting technique, daylighting can reduce electrical lighting energy use by up to 40 percent and reduce peak cooling demand. It is critical to achieving sustainability goals set by the United States Department of Energy (DOE) and the United States Green Building Council (USGBC), as well as initiatives proposed by Architecture 2030.
Turning off or dimming electric lights when natural light is available are fundamental to reducing electrical energy use. So are using lighting controls. A good design should document daylight zones and independent control zones. Plans should also show where photosensors should be located and identify the light fixtures that are controlled by individual sensors.
To reap the benefits of daylighting, use lighting controls that either manually or automatically switch off or dim the electric lights in response to available natural light. Control technologies include sensors, dimmers, and switches. Photocontrols are a basic control technology for daylighting. Components include the light source, the control unit (dimmer or switch), the photo sensor, and the controller. Other control strategies include using time clocks or occupancy sensors. These technologies turn off lights gradually or automatically depending on the strategy chosen.
The electric lighting system should be designed with daylighting in mind. The system should be laid out in a pattern that coincides with the available daylight and is circuited parallel to the daylight contours. Aligning the circuits with daylight provides more ability to control the electric light in response to available natural light. All lights that are going to be controlled together should be organized into control zones. Ideally these zones will have uniform daylight levels and similar lighting needs. All the luminaires in the control zone should be on one lighting circuit or subcircuit to simplify installation and provide flexibility for future changes.
The type of system dictates where the photosensor must be mounted to accurately read light levels and control the electric light accordingly. In a closed loop system the photosensor monitors the total light level (daylight and electric light) within the space (usually the light levels at the worksurface, such as a desk or table). The best location for a photosensor is above an unobstructed location above a workstation. Beware of cubicle office environments that can cause shading problems.
In an open loop system the photosensor monitors the available daylight level at the daylight aperture (window, skylight, clerestory). The photosensor should be placed within the window frame or extremely close or within the skylight well.
Successful Daylighting Control
Ensuring that a daylight-designed building achieves both the promised energy savings and occupant benefits requires good planning, coordination, and communication. Successful control systems are not simply a matter of choosing products from a catalog of options. The architect must select the appropriate strategies and equipment for the application. Decisions about the electric lighting, daylighting, and control systems should not be made independently of one another. Nor should they be made independently of decisions such as building orientation, window and/or skylight design, and building use and occupancy schedules.
An integrated design process can be used to create a building that performs as promised. So can commissioning building systems, including daylighting controls. Ideally, the lighting system should be calibrated after the building is occupied. Architects can achieve the potential energy savings and related environmental benefits of daylighting design. A little research and education on controls can make a design a performance success and a beautiful space for occupants.
A good resource for more information is the Daylighting Collaborative website or the Advanced Lighting Guidelines, 2003 (Section 8.4 Daylighting Controls, pages 8 to 34).
Abby Vogen Horn (email@example.com) is a senior project manger with the Daylighting Collaborative, a project of the Energy Center of Wisconsin. She has been working in the field of daylighting for more than 10 years.