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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 driverâs 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 â¢ Choose the LED source color to properly render sign colors. A higher CRI LED will provide the best color appearance. â¢ 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.