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Troy, N.Y. -  3/13/2009

ASSIST recommendation provides new evaluation metric for parking lot luminaires

Parking lot and outdoor luminaires are a rapidly growing market for the LED lighting industry, and many LED-based outdoor luminaires have entered the marketplace with claims of significant energy savings and life-cycle cost reductions compared to traditional luminaires. However, some of these LED systems are not realistically able to meet the requirements of good outdoor lighting, and no simple method exists to evaluate and compare the performance of outdoor lighting systems before selection and installation.

To help outdoor lighting designers and specifiers make optimum luminaire choices, the Alliance for Solid-State Illumination Systems and Technologies (ASSIST) has published a new volume in its ASSIST recommends series about parking lot lighting. The issue “Recommendations for Evaluating Parking Lot Luminaires” describes a new, alternative metric for evaluating parking lot luminaires based upon how well they cater to the application’s requirements. The metric was developed through previous research by the Lighting Research Center (LRC) and builds upon the concept of application efficacy.

The volume is available for free download from the ASSIST Web site: www.lrc.rpi.edu/programs/solidstate/assist/parkinglot.asp

Application efficacy and catering to an application’s requirements

The concept of application efficacy1 refers to only the flux leaving the luminaire in a particular direction, specifically toward the task area, rather than the total amount of flux exiting the luminaire or the light source’s luminous efficacy.

“We know that luminous efficacy and luminaire efficacy are not accurate gauges for how appropriately and efficiently a luminaire will meet an application’s lighting needs,” says Yutao Zhou, a research scientist at the Lighting Research Center and one of the designers of ASSIST’s new parking lot luminaire metric. “If a luminaire is not designed well to collect all the flux emitted by the light source and direct it to where it is needed, then the application may not be energy efficient,” he says. For example, a parking lot luminaire that loses some light upward to the sky will not be as efficient as one that directs more flux down to the parking lot’s pavement, from the standpoint of application efficacy.

Zhou notes that ASSIST is not questioning the relevance or appropriateness of existing standards for outdoor and parking lot lighting, but rather accepts the standards as they are and integrates them into ASSIST’s new, recommended metric for parking lot luminaires.

Metric definition

The application’s task area is of central importance to ASSIST’s new metric, and is defined as a function of the luminaire type and its mounting height. Once the task area is defined, it is divided into sections, or cells, and the illuminance reaching each cell is calculated from a given luminaire’s IES file. Cells that have illuminances falling above or below existing application standards (e.g., IESNA’s RP-20-98 Lighting for Parking Facilities) are discounted. The luminous flux of the conforming cells is then used to calculate the total useful luminous flux reaching the task area, which is then multiplied by the percentage of conforming cells in the task area and divided by the input power to obtain the final luminaire system application efficacy. The ASSIST publication provides step-by-step instructions for calculating the luminaire system application efficacy for parking lot luminaires, and may be used to calculate the efficacy of one luminaire or for an entire parking lot.

About ASSIST

ASSIST is a collaboration between researchers, manufacturers, and government organizations. Its goal is to identify and reduce major technical hurdles currently facing solid-state lighting. The Lighting Research Center conducts research, demonstration, and educational activities on behalf of ASSIST.

ASSIST is sponsored by Acuity Brands Lighting; Bridgelux; China Solid State Lighting Alliance; Cree; Everlight Electronics Co., Ltd.; Federal Aviation Administration; GE Lumination; ITRI, Industrial Technology Research Institute; Lighting Science Group; Lite-On; NeoPac Lighting; New York State Energy Research and Development Authority (NYSERDA); OSRAM SYLVANIA/OSRAM Opto Semiconductors; Permlight; Philips Color Kinetics; Photonics Cluster (UK)/The Lighting Association; Seoul Semiconductor; United States Environmental Protection Agency; USG; WAC Lighting.

About ASSIST recommends

ASSIST has developed a publication program called ASSIST recommends to provide a set of formal recommendations to the LED and lighting communities about issues important for the reliable performance of LED lighting and its comparison to other light source technologies. The publications include recommendations for LED life definition, testing and measurement, best practice guides for different lighting applications, and recommendations for selecting LED lighting. Unlike traditional test procedures that require products to be tested under standardized, ideal conditions, ASSIST recommends methods call for testing products under conditions similar to those found in the application environment, where the light source could experience many different temperatures and may perform poorly as a result. Testing products by intended application also allows for apples-to-apples comparisons of product performance because test methods have been developed from a technology-neutral standpoint. ASSIST recommends publications are developed under the guidance of ASSIST sponsors using research conducted by the Lighting Research Center (LRC). Each publication undergoes internal review, first by LRC researchers and then by ASSIST sponsors. Industry input also is gathered during the writing process through one or more roundtable sessions hosted by ASSIST and the LRC. Based upon this industry input, the publications are revised and then published online for free download.

As warranted, the publications are updated from time to time to reflect new research, technologies, methods, and equipment.


Rea MS, Bullough JD. Application efficacy. Journal of the Illuminating Engineering Society 2001; 30(2): 73–96


About the Lighting Research Center
The Lighting Research Center (LRC) at Rensselaer Polytechnic Institute is the world's leading center for lighting research and education. Established in 1988 by the New York State Energy Research and Development Authority (NYSERDA), the LRC has been pioneering research in solid-state lighting, light and health, transportation lighting and safety, and energy efficiency for nearly 30 years. LRC lighting scientists with multidisciplinary expertise in research, technology, design, and human factors, collaborate with a global network of leading manufacturers and government agencies, developing innovative lighting solutions for projects that range from the Boeing 787 Dreamliner to U.S. Navy submarines to hospital neonatal intensive-care units. LRC researchers conduct independent, third-party testing of lighting products in the LRC's state of the art photometric laboratories, the only university lighting laboratories accredited by the National Voluntary Laboratory Accreditation Program (NVLAP Lab Code: 200480-0). In 1990, the LRC became the first university research center to offer graduate degrees in lighting and today, offers a M.S. in lighting and a Ph.D. to educate future leaders in lighting. With 35 full-time faculty and staff, 15 graduate students, and a 30,000 sq. ft. laboratory space, the LRC is the largest university-based lighting research and education organization in the world.

About Rensselaer Polytechnic Institute
Rensselaer Polytechnic Institute, founded in 1824, is America’s first technological research university. The university offers bachelor’s, master’s, and doctoral degrees in engineering; the sciences; information technology and web sciences; architecture; management; and the arts, humanities, and social sciences. Rensselaer faculty advance research in a wide range of fields, with an emphasis on biotechnology, nanotechnology, computational science and engineering, data science, and the media arts and technology. The Institute has an established record of success in the transfer of technology from the laboratory to the marketplace, fulfilling its founding mission of applying science “to the common purposes of life.”