Using Luminance for Design and Evaluation of Energy Efficient and Sustainable Luminous Environments to Supplement Current Illuminance-Based Design Codes

Abstract

Illuminance and illuminance-based metrics have been adopted in lighting design and field measurement over the past century to support the notion that the primary function of lighting is for task performance and visibility. However, illuminance and illuminance-based metrics, which are commonly measured on target planes, are only a portion of the lighting metrics necessary to quantify the luminous environment. There is a lack of direct relationship between light on surfaces and the vision of human eyes, which covers not only targets and surfaces but also immediate and far backgrounds. Therefore, illuminance and illuminance-based metrics are, by nature, not able to directly interpret visual performance of space occupants. However, luminance, the quantity of light reflected from a surface and transmitted into a space and eventually arriving at the eyes of space users, is a direct stimulus of vision. This study explored using perceivable luminance for design and evaluation of energy efficient and sustainable luminous environments to supplement current illuminance-based design codes. The relationship between task-based illuminance, as used in the existing codes, and the luminance of the environment perceived by a simulated space user was explored through computer simulations and field measurements using HDR imaging. The goal was to incorporate the use of luminance as the primary design metric for efficient lighting design. Evaluations were conducted for a personal office absent of daylighting. Computer simulations conducted in AGI32 were assessed to determine variance of lighting layouts possible with current illuminance-based design standards. A total of twelve lighting designs (six LED, six fluorescent) were considered and evaluated. Field measurement and HDR images obtained from previous studies were evaluated to recognize luminance preferences among 30 study participants. Results from the study indicate luminance distribution is dependent on lighting layout and directly affected by the light source. Decreasing general lighting levels and increasing task lighting levels could improve the satisfaction of space users and reduce lighting energy consumption.