Research Project Summary Information
Innovative Energy-Efficient Lighting for New York Roadways(ST9815-1)
Rensselaer Polytechnic Institute-LRC
Lighting along roadway and highways serves a primary purpose of safety by supporting visibility of pedestrians, vehicles, and other potential hazards for drives. Lighting is used to illuminate intersections and crossings and sections of roadways located in rural and suburban areas where the recommended light levels are lower than in urban areas (IENSA, 2000). In New York State, an estimated 1.1 billion kilowatt hours (kWh) of electricity per year is currently used for roadway lighting, equivalent to burning approximately 320,000 tons of coal, with corresponding emissions of approximately 740,000 tons of CO2, 6200 tons of SO2, and 2700 tons of NOX compounds (EPA, 1993).
Under low-light, mesopic, conditions, the human visual system used both cone and rod photoreceptors for vision. Rods and cones respond differently to different parts of the visible light spectrum. At high light levels, the cone photoreceptors dominate vision and are most sensitive to the visible wavelength of 555 nanometers (yellow-green light). Rods dominate vision under low light conditions and are most sensitive at 505 nanometers (blue-green light). Sodium lamps (HPS) lamps are predominantly used for roadway lighting in New York State (ICF Consulting and LRC, 2001). Since HPS are yellowish in color, there may be significant opportunity for greater energy efficiency in roadway lighting applications with light sources more tuned to the blue-green wavelength.
The Contractor shall conduct the following tasks: (1) Review lighting policies and standards in New York State; (2) Conduct interviews and surveys with transportation engineers in New York State involved in lighting decision making to assess awareness of issues related to mesopic vision, light source spectrum (color), visibility, and roadway types; (3) Take field measurement of light levels and lamp types used on roadways in New York State; (4) Conduct human factors meta-analysis of lighting approaches to improve visibility and safety along roadways using innovative lighting systems.
Replacing sodium-based roadway lighting with lighting that is tuned to mesopic vision sensitivity may provide significant energy savings without sacrificing any night-time visibility. Field measurements were taken of light levels and lamp types installed in urban, suburban and rural regions of New York State. The field research showed that opportunities to reduce lighting levels without sacrificing visual performance are greatest in rural and residential locations where light levels are lowest and mesopic conditions exist. The research revealed the potential to significantly reduce light levels under low light conditions.
The review concluded that New York State Department of Transportation (NYSDOT) generally pays for the design and installation of lighting, and municipalities are responsible for maintenance and operation costs. NYSDOT publishes three documents relating to roadway lighting: Policy on Highway Lighting (1979); Highway Design Manual (1995); and Standard Specifications (2006). The Highway Design Manual prefers semi-cutoff (cobrahead shaped) High Pressure Sodium (HPS) luminaires for roadway lighting. Municipal codes typically limit glare and light trespass, and a few of the codes required minimum light levels for some outdoor/public lighting installations.
Sixty-five percent of the transportation officials surveyed were familiar with mesopic research and 25 percent had considered revising their lighting practices as a result of this research. Lamp efficacy and life maintenance typically dictate what lamps are used in roadway lighting, and 75 percent of respondents reported almost exclusively using HPS lamps for roadway illumination.
A comparison of the energy and economic performance of the two white light (bluer) sources, metal halide and induction, to HPS light sources, showed that HPS lighting systems are the least expensive option for most installations. HPS will continue to be the favored roadway lighting option until the price of the alternative white light sources (metal halide, induction, and light-emitting diode) can compete with the low cost of HPS roadway li
Rensselaer Polytechnic Institute-LRC
21 Union St
Troy, NY 12180
Rensselaer Polytechnic Institute
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