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Quick and Easy Web-Based Assessment Tool for Day/Electric Lighting

To help architects, engineers, lighting designers, and consultants meet or exceed increasingly stringent Title 24 (California's building energy-efficiency standard) requirements, Southern California Edison and other California utilities have been developing tools for the Savings by Design program. This program aids building managers, who often lack an easy and quick means of assessing daylighting and electric lighting performance. When lighting decisions are made, key parameters that impact energy use and affect the quality of the luminous environment need to be taken into consideration. These factors include window size and orientation, glazing type, luminaire types and layout, and reflectance of interior surfaces, among others.

To consider daylighting and electric lighting performance properly, decision makers need to use lighting-simulation tools, which compute work-plane illuminance and, in many cases, surface luminance values. However, such tools have long learning curves and are time consuming, which increases design costs. There is a clear need to provide options for assessing quantitative and qualitative aspects of daylighting and lighting designs that beat Title 24 requirements but in a more cost-effective manner than through the conventional use of simulation tools.

To address this need, EETD's Building Technologies Department is developing a web-based tool that allows lighting and daylighting designers to quickly and easily assess the effects of key parameters on qualitative and quantitative aspects of daylighting and lighting performance. The tool uses a large database of images and statistical data, which were generated through many parametric lighting simulations in prototypical architectural spaces. The data were generated with the Radiance lighting simulation and rendering software (http://radsite.lbl.gov). The end result is equivalent to a web-based, virtual lighting simulator, which allows users to change the values of key design and context parameters and displays the corresponding images and data for qualitative and quantitative assessment of luminous performance. The tool, currently referred to as the "Radiance Image Database," is available at http://gaia.lbl.gov/rid. The current version includes two main modules, one focusing on daylighting in a small office space and the other on electric lighting in five space types: a classroom, a small office space, a large open office space with partitions, a large warehouse, and a small retail store. The web-based user interface allows quick and easy selection of values for the key parameters that were varied in the simulations and provides instant response by displaying the corresponding pre-calculated images and data.

The user interface is designed to allow side-by-side comparison of alternative scenarios or of the same scenario in different display modes. The display modes include a "camera exposure" display, which is the equivalent of what a camera would produce in an average exposure mode; a "human exposure" display, which adjusts the image to reflect the sensitivity and adaptation of the human eye; and "iso-contour" and "false-color" displays, for quantitative assessment (see Figure 1).

Room in camera exposure mode, based on average luminance Room in camera exposure mode with superimposed iso-contour lines of luminance or illuminance Room in human exposure mode, based on the sensitivity and adaptation of the human eye Room in false color mode, showing magnitude of luminance or illuminance

Figure 1. Each image is available in four display modes: camera exposure, based on average luminance (top left), camera exposure with superimposed iso-contour lines of luminance or illuminance (top right), human exposure, based on the sensitivity and adaptation of the human eye (bottom left), and false color mode, showing magnitude of luminance or illuminance (bottom right).

The output includes perspective views of the architectural spaces, showing luminance values, and plan views, showing work-plane illuminance values. Quantitative statistical information is also provided in the form of minimum, average, and maximum work-plane illuminance. The electric lighting module also includes quantitative information about installed and used lighting power density; the latter varies for scenarios with dimmed and/or switched lighting fixtures. All lighting designs are at least 10 percent more energy efficient than Title 24, to demonstrate the effectiveness and encourage the use of energy-efficient lighting designs.

Screenshot of the Radiance Image Database Browser

Acknowledgments

The development of the Radiance Image Database was supported with funding from Southern California Edison (SCE) through the California Institute for Energy Efficiency (CIEE), a research unit of the University of California. Publication of research results does not imply endorsement of or agreement with these findings by CIEE or any CIEE sponsor. This work was also supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Building Technology, State and Community Programs, Office of Building Systems of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098. The architectural and electric lighting designs were based on input from Lisa Heschong from the Heschong Mahone Group and James Benya of Benya Lighting Design. The development team included Judy Lai, Daniel Fuller, and Tara Tariq.

— Konstantinos Papamichael

For more information, contact:

  • Konstantinos Papamichael
  • (510) 486-6854; fax (510) 486-4089

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