Establishment of a National Specification for Use of LED Roadway Lighting

The lighting industry has changed dramatically over the past decade. Roadway luminaires have moved beyond the limits of a single lamp and reflector design into the vast possibilities presented by light emitting diodes (LED), which also boast lower energy usage and improved color. The optics of legacy high pressure sodium (HPS) full-cutoff luminaires that manufacturers had to work with were restricted to the lamp and reflector design in that lamps emitted light in almost every direction which was then reflected to get to the roadway. There was only so much control possible with this configuration, which resulted in a gentle gradient at the edges of the distribution pattern and “spill” light outside of the calculation grid. American Association of State Highway and Transportation Officials (AASHTO) target light levels are calculated over a grid limited to the traveled roadway. Any light that landed outside of the calculation grid is not quantified in the average and uniformity results, but is still present with the distributions of HPS cobra head luminaires. With the greater ability to control the distribution and sharp cutoff at the edges with LED luminaires, light levels beyond the calculation grid may be dramatically reduced but a design may still meet the AASHTO criteria. Therefore, this should be investigated and if the results dictate, AASHTO should provide specific light-level criteria for areas immediately adjacent to the traveled roadway when using LED. Additionally, the possibility of dimming introduces some liability, and the difference in spectral power densities of LED luminaires has shown other potential impacts involving both weather conditions and nature. Currently, there are no published recommendations by AASHTO regarding dimming in response to time of day or traffic volumes. Without further research into these issues, liability increases for departments of transportation (DOTs) using this technology. The objective of this research is to establish an application specification for LED roadway lighting addressing issues of liability for departments of transportation. This study is expected to build upon, complement, and advance the ongoing efforts of the AASHTO Roadway Lighting Committee revolving around the usage of LED lighting. This research is expected to include the following tasks: (1) Evaluate the off-axis lighting levels at both HPS- and LED-illuminated highway interchanges, including shoulders and the clear zone beyond the shoulders. Identify the average foot-candle (fc) and uniformity ratio for both systems, and identify whether there exists a difference in average fc and uniformity of the shoulder, and whether this negatively impacts the safety benefits of installing lighting. (2) Based on the results of Task 1, establish target light levels of average fc and uniformity for areas beyond the traveled lanes as to not decrease the level of safety afforded by legacy HPS systems. (3) Study the effects of white light sources in foggy conditions, where higher color temperatures and different wavelengths of light react differently than legacy HPS sources. Compare various color temperatures and spectral power densities over a range from 2200K HPS to 5700K LED. Use these results to develop guidelines for designing in areas with a high likelihood of foggy conditions. (4) Study the effects of various color temperature sources and the attraction of insects to these sources, specifically near bodies of water. Compare multiple LED cobra head luminaries to legacy HPS cobra head luminaires to determine if high color temperature LED luminaires attract insects which could negatively affect the safe travel of roadways. (5) Evaluate the liability of reducing light levels during times of traffic volumes lower than the design values. Provide recommendations in the application of dimming roadway lighting in order to limit liability to state DOTs.


  • English


  • Status: Proposed
  • Contract Numbers:

    Project 05-22

  • Sponsor Organizations:

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001

    American Association of State Highway and Transportation Officials (AASHTO)

    444 North Capitol Street, NW
    Washington, DC  United States  20001

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Project Managers:

    Harrigan, Edward

  • Start Date: 20160509
  • Expected Completion Date: 0
  • Actual Completion Date: 0
  • Source Data: RiP Project 40800

Subject/Index Terms

Filing Info

  • Accession Number: 01598919
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 05-22
  • Files: TRB, RiP
  • Created Date: May 8 2016 1:00AM