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Solid-State Roadway Lighting Design Guide: Volume 1: Guidance (2020)

Chapter: Chapter 9 - Roadway Sign Lighting

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Page 51
Suggested Citation:"Chapter 9 - Roadway Sign Lighting." National Academies of Sciences, Engineering, and Medicine. 2020. Solid-State Roadway Lighting Design Guide: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25678.
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Page 51

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44 Chapter 9 - Roadway Sign Lighting Current Guide The current AASHTO guide was updated to include sign luminance levels based on the visual complexity of the roadway surroundings. Uniformity levels are also given for the signs. The color of the light source as well as placement is also discussed. Additional Considerations for LED Sources Using an LED light source can provide additional options for sign lighting that are not available with traditional light sources. Light sources can be placed to use the sign sheeting retro-reflectivity to enhance the sign luminance and reduce the over-lighting and waste of light seen with traditional sources. LEDs can provide tight optical control that will limit the light output to the sign face itself. This will limit the amount of light spread past the sign. Consider also an alternative light source location. Using a very tightly controlled LED luminaire, the light source can be placed remote from the sign and the light projected to the sign face from up to 100 hundred feet from the sign location. Locate the source in the general direction of the driver’s approach aimed at the sign to see any retroreflective benefit. This installation method allows for the use of the sign reflectivity to better provide the sign luminance than in typical installations. This installation is more closely aligned with the headlamp performance, which is the design mode of the sign sheeting. This approach to lighting may also reduce maintenance issues because the LED can be serviced from the side of the road rather than over the roadway on the sign truss. Key Issues • Choose the LED source color to properly render sign colors. A higher CRI LED will provide the best color appearance. • Minimize over-lighting and waste of light beyond the sign itself by using a tight optical control limiting the light from the luminaire to within the sign extents from the LED.

Next: Chapter 10 Operations and Maintenance Considerations »
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The lighting industry has changed dramatically over the past decade. The optical system design of legacy high-intensity discharge (HID) luminaires was restricted to the lamp, refractor, and reflector design, which had limits in the distribution of the light, controls, and adaptability. Roadway luminaires have moved beyond this design methodology to include the vast possibilities presented by solid-state lighting (SSL). At present, in the form of light emitting diodes (LED), SSL uses lower energy, reduces maintenance, improves color, and can be easily dimmed and controlled.

The TRB National Cooperative Highway Research Program's pre-publication draft of NCHRP Research Report 940: Solid-State Roadway Lighting Design Guide: Volume 1: Guidance develops more comprehensive guidelines in American Association of State Highway Transportation Officials (AASHTO)-standard format for the application of roadway lighting related to the widespread adoption of SSL, and identifies gaps in knowledge where possible future research will enhance these guidelines.

Also see this guide's accompanying pre-publication draft, NCHRP Research Report 940: Solid-State Roadway Lighting Design Guide: Volume 2: Research Overview.

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