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For Immediate Release

Contact:   Rebekah Mullaney
Lighting Research Center
518.687.7118
mullar2@rpi.edu
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Troy, N.Y. -  10/30/2009

Proven Method Available to Significantly Reduce Energy Consumption in Street Lighting

Improved measurement techniques could cut costs and improve visibility perception

LRC experts estimate that about half of the approximately 13 million streetlights in the United States have the opportunity to significantly reduce energy consumption by as much as 50 percent, translating to an annual savings of 1 billion kWh, and a reduction in power plant CO2 emissions of 546,000 tons per year.

LRC researchers demonstrated in multiple field tests that, by using what they describe as a Unified System of Photometry, a street lighting system can be designed to reduce energy use while maintaining or improving perceptions of visibility, safety, and security.

“In nighttime conditions, the human eye is more sensitive to short-wavelength light, which produces ‘cool’ tones like blue or green, as opposed to long-wavelength light, which produces ‘warm’ tones like yellow and red,” said LRC Director of Energy Programs Peter Morante. “By replacing traditional, yellowish high-pressure sodium (HPS) lights with ‘cool’ white light sources, such as induction, fluorescent, ceramic metal halide, or LEDs, we can actually reduce the amount of electric power used for lighting while maintaining or even improving visibility in nighttime conditions.”

The eye has two types of visual receptors in the retina, cones and rods. The current system of photometry—the measurement of visible light in terms of human perception for certain activities like reading and seeing fine details—is based on how some cones respond to different wavelengths. Cones are the dominant visual receptor under photopic (daylight) lighting conditions. Rods function primarily under very dim conditions. According to Morante, it is necessary to redefine the luminous efficacy functions needed for nighttime applications where electric lighting is used and both rods and cones contribute to vision The LRC’s Unified System of Photometry was designed to characterize light at any level, including the mesopic level where both rods and cones operate.

LRC field demonstration results from the past few years in rural and suburban areas of Connecticut, Massachusetts, and Texas verified that by implementing the Unified System of Photometry the street lighting system consumed 30 to 50 percent less electric power and the residents believed they could see better and said they felt safer, when compared to lighting systems designed using the traditional system of photometry. The Unified System of Photometry provides an objective method for optimizing light source spectra for minimal energy use while maintaining good visibility, according to the LRC researcher team.

There is now renewed interest in the research, according to Morante, as an increasing number of cities and towns across the country are examining ways to save energy either through a reduction or a change in outdoor lighting. And the interest seems to be spreading.

According to LRC Director Mark Rea, Ph.D., researchers around the world are also concluding that the current system of photometry could use some updating to better characterize light source performance under nighttime conditions. The International Commission on Illumination, also known as the CIE from its French title, the Commission Internationale de l'Eclairage, will be releasing its own form of unified photometry for outdoor lighting, explained Rea, a long-standing CIE member.

A full report detailing energy use, consumer acceptance and perceptions, visibility, and light levels for one of the LRC’s field tests in the City of Groton, Connecticut, was published last year and is available for free download.

In the LRC field studies, the mesopic street lighting system met all utility requirements and, in addition to significant reductions in energy consumption, was preferred by residents over the yellow-appearing HPS system.

The following technical papers explain the Unified System of Photometry:

  • Rea, M., J.D. Bullough, J.P. Freyssinier, and A. Bierman. 2004. A proposed Unified System of Photometry. Lighting Research and Technology 36(2): 85-111.
     
  • Rea, M., Z. Yuan, and A. Bierman. 2009. The Unified System of Photometry Applied to Remote Airfield Lighting. Lighting Research and Technology 41(1): 51-70. 

In January 2009, the Alliance for Solid-State Illumination Systems and Technologies (ASSIST) published a volume in its ASSIST recommends series, “Outdoor Lighting: Visual Efficacy,” which also describes the Unified System of Photometry. The publication can be downloaded for free.

Learn more about LRC’s outdoor and street lighting research at these LRC Program pages:


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 energy and the environment, light and health, transportation lighting and safety, and solid-state lighting for more than 25 years.
In 1990, the LRC became the first university research center to offer graduate degrees in lighting and today the LRC offers both a M.S. in lighting as well as a Ph.D. to educate future leaders in lighting. Internationally recognized as the preeminent source for objective information on all aspects of lighting technology and application, 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). LRC researchers are continuously working to develop new and better ways to measure the value of light and lighting systems, such as the effect of light on human health, and the effect of light on plant physiology.
The LRC believes that by accurately matching the lighting technology and application to the needs of the end user, it is possible to design lighting that benefits both society and the environment.

About Rensselaer Polytechnic Institute
Rensselaer Polytechnic Institute, founded in 1824, is the nation's oldest technological university. The university offers bachelor's, master's, and doctoral degrees in engineering, the sciences, information technology, architecture, management, and the humanities and social sciences. Institute programs serve undergraduates, graduate students, and working professionals around the world. Rensselaer faculty are known for pre-eminence in research conducted in a wide range of fields, with particular emphasis in biotechnology, nanotechnology, information technology, and the media arts and technology. The Institute is well known for its success in the transfer of technology from the laboratory to the marketplace so that new discoveries and inventions benefit human life, protect the environment, and strengthen economic development.