Field and Software Evaluation of Illuminance from LED Luminaires for Roadway Applications

Field measurements and lighting analysis software were used to conduct an evaluation of the illuminance of LED roadway luminaires. Three sets of recently developed LEDs and one set of high-pressure sodium luminaires were installed in the field, and data were collected separately for each luminaire according to Illuminating Engineering Society of North America (IESNA) LM-50-99. Photometric characteristics provided by the manufacturers of the luminaires were used to assess their performance with AGi32 lighting analysis software, and the results were compared with the field illuminance data. Results showed that field illuminance was sometimes lower than the illuminance indicated by the software; these differences varied in both magnitude and location, depending on the LED luminaire. Multiplicative factors to describe the differences were estimated and ranged from 0.96 (relatively small) to 0.57 (relatively large). Larger differences were located near the light poles and at the middle and third points of the span. These findings suggest that quick checks can be performed by taking illuminance measurements at key points along the span to provide an approximation of the differences between field and software data. Discrepancies between software and field data may be very important in the selection of luminaires for a given road and pedestrian conflict classification, as the field illuminance may not reach minimum levels required by public agencies. This point is illustrated with an example that uses minimum requirements from the Illinois Department of Transportation. Full sets of repeated field data points for state-of-the-art LED roadway luminaires, collected according to IESNA LM-50-99, are presented.