Chapter 14 - Lighting

14.4. Lighting Calculations

As part of the steps for determining the appropriate lighting system for a particular project, the lighting designer must calculate the required illumination.  Various factors are considered when making this determination, such as roadway width, lighting setback and mounting height, and the type of lighting system to be used.  The designer determines the lighting calculations for a particular project by using a computer program, such as AGi32 by Lighting Analysts, Inc..  The calculation shall show illuminance values on the roadway with point to point intervals of 6-ft. longitudinally and transversely.  Also, when a section of roadway is being analyzed, the entire section of roadway that is being illuminated shall be analyzed completely as a self-contained area.

The lighting calculations shall show the tabulated values for average, minimum and maximum footcandles, uniformity and veiling luminance ratios.  The lighting designer shall submit files of the complete roadway or area under consideration with point by point illuminance values in Adobe Acrobat (.pdf) format.  It may be necessary for the lighting designer to consider other lighting options and to substantiate that the lighting design is optimum and cost effective.   The lighting designer shall be prepared to explain the lighting system choice and present all documentation to GDOT to substantiate the lighting recommendation.