by Konstantinos Papamichael

To help architects, engineers, lighting designers, and consultants meet or exceed the increasingly stringent requirements of the California building energy efficiency standard known as Title 24, Southern California Edison and other utility companies have been developing tools for the Savings by Design program. These tools aim to help building designers, owners, and managers who often lack an easy way to assess daylighting and electric lighting performance.

Informed lighting decisions take into consideration key factors that affect energy use and the quality of the luminous environment. 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 often have long learning curves and may be time consuming to use, which can increase design costs.

To provide an option for assessing lighting designs without running detailed simulations, we at the Building Technologies Department of the Environmental Energy Technologies Division (EETD) at Lawrence Berkeley National Laboratory (LBNL) are 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.

Simulating Lighting Scenarios

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.

The new Web-based tool, known as the "Virtual Lighting Simulator," 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 current version includes two main modules, one for assessing daylighting in a small office space and the other for electric lighting in five space types: a classroom, a small office , a large open office with partitions, a large warehouse, and a small retail store.

Presenting Results

The Web-based user interface allows quick and easy selection of values for the key parameters that were varied in the simulations, and the tool provides an instant response in the form of a display of previously calculated images and data.

The user interface is designed to allow side-by-side comparisons of alternative scenarios or of the same scenario in different display modes. The four display modes are a "camera exposure" display, which is the equivalent of what a camera would produce in an average exposure mode; a "human perception" 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.

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 power used 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.

Future development of the tool will incorporate feedback from users.

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The Virtual Lighting Simulator allows users to modify lighting parameters and compare two scenarios. This example compares lighting systems for a large open office space. Image: EETD/LBNL A calculated view of a small retail space, displaying what a camera would see, with superimposed iso-contour lines of luminance or illuminance. Image: EETD/LBNL The Virtual Lighting Simulator displaying differences in daylight due to two glazing types in a small office. Image: EETD/LBNL A simulation of changes in electric lighting system and wall/ceiling reflectance in two small offices. Image: EETD/LBNL "False-color" display of the lighting differences between two configurations of a classroom setting. Image: EETD/LBNL Display of the difference between camera exposure (left) and human perception (right) in a warehouse space. Image: EETD/LBNL   Click on thumbnail images to view full-size pictures.