Does a light shine if no one sees it? Yes, and it wastes a lot of power, according to Dorukalp Durmus, assistant professor in the Penn State Department of Architectural Engineering, who was recently awarded a U.S. Department of Energy (DOE) Buildings Energy Efficiency Frontiers & Innovation Technologies (BENEFIT) grant.
With the $450,000 in funding over three years, Durmus will develop a framework to measure the relationship between electrical power used by lighting hardware and the amount of useful light generated for building occupants. His co-collaborators on the grant are Wendy Davis, associate professor of lighting, and Wenye Hu, associate lecturer of illumination design, both with the University of Sydney’s School of Architecture, Design and Planning in Australia.
“Lighting consumes approximately 18% of electricity in buildings,” Durmus said. “And there has been significant investments and efforts dedicated to improving the energy efficiency of lighting hardware, which has had some success — the widespread commercialization and adoption of light-emitting diodes (LEDs) has notably reduced energy consumed by lighting in the United States. However, there are physical limits to the efficiency with which light can be generated by electricity, so the strategy of improving lighting hardware alone cannot produce energy conservation gains indefinitely.”
Lighting energy efficiency is measured by luminous efficacy, or lumens per watt — the visible light produced by one watt of electricity. According to Durmus, the measurement provides a reliable metric to quantify the energy efficiency of individual lighting devices but does not address how light is used in buildings. To address this issue, Durmus proposed that the “application efficacy” may be a better way to measure the usable visible light produced by a unit of electrical power.
A person can visually perceive their space, which includes walls, objects and people, through light hitting the surfaces of things and reflecting to their eyes. But a person cannot see all of their space at once.
“Since only a fraction of light generated is seen by building occupants at any moment, significant electrical power goes to waste,” Durmus said. “Several modern lighting design practices perpetuate this problem.”
Decades-old lighting application performance standards recommend uniform lighting indoors, allowing an occupant to engage in a variety of visual tasks without needing to adjust the lighting — resulting in wasted light and wasted energy, according to Durmus. He pointed to more recent research that has produced such ideas as “smart” dimming systems and more advanced approaches that could tailor the spectrum of light to individual objects, reducing light absorption, or gaze-dependent lighting systems that illuminate only where the viewer is looking.
“These approaches could save substantially more energy but would require more drastic changes to both lighting product design and architectural lighting design practices,” Durmus said. “Yet, they still don’t necessarily quantify the power used to generate light used. The ability to measure application efficacy will drive the adoption of more energy-efficient design practices, foster product innovation and, ultimately, reduce the energy consumed by lighting.”
Durmus and his co-collaborators plan to develop a method for measuring lighting application efficacy, as well as a framework for improving the metric with future research.
“The model that will guide this research is based on the primary pathway of light in architectural settings: the generation and emission of light from a luminaire, the travel of the light through the space and into the eyes of occupants and the process of visual perception,” Durmus said.
The researchers will mathematically quantify how efficiently the lighting hardware outputs light, how efficiently that light illuminates space within an occupant’s visual field and how sensitive an occupant is to the light emitted. Once they develop the metric of lighting application efficacy, they will finetune it with experiments and computational modeling, including specific adjustments that can be made based on the efficiency changes in luminaires as a function of operating time.
“This work is intended to not only provide a functional measurement method and framework for future research in the area but to also facilitate advancement in lighting design practices,” Durmus said. “The proposed work will serve as an impetus for the lighting design community to critically examine standard practices and re-think the customs and traditions that are no longer advancing the field.”