In a new report entitled Specifier Reports: Streetlights for Local Roads, the Lighting Research Center (LRC) evaluated four LED-based street lights, and one induction light, relative to a baseline high-pressure sodium (HPS) light. Only one of the solid-state-light (SSL) luminaires matched the HPS light in terms of pole spacing when tested to ANSI/IESNA RP-8 requirements.

The LRC evaluated the lights based on a theoretical one-mile stretch of residential roadway, and determined the number of lights (and therefore poles) that would be required to meet RP-8 illumination levels. The results are stated in terms of poles per mile required to meet RP-8 and the research also includes energy consumption expressed in watts per mile. The report also includes life-cycle cost per mile data.

The LRC purchased the LED and induction lights after asking manufacturers’ representatives to recommend lights equivalent in illumination to a 100W HPS light. The purchased lights emit a Type II beam pattern based on a full cutoff cobra-head design.

The different LED lights tested required 3% to 92% more poles relative to the HPS baseline. The induction light from GE Lighting required 64% more poles.

In power consumption, the LED lights range in usage from 42% less than the HPS case to 15% more wattage per mile. While all of the LED lights were lower in power consumption than the HPS light, the need for more lights per miles resulted in the LED lights needing more power in some cases. The induction light required 41% to 51% more power based on whether the installation used lights staggered on both sides of the roadway or installed on a singles side.

As a previous LRC report found, the life-cycle costs were dominated by the pole and installation costs. For an assumed LED module replacement cycle of 25,000 hours, the average life-cycle cost for the LEDs was 1.9 times greater than for the HPS light. That premium drops to 1.6 based on a 50,000 hour life cycle for the LEDs.

The good news, from the LED perspective, is that one luminaire came close to matching the HPS performance. The BetaLED STR-LWY-2M-HT-04-C-UL-SV luminaire supported 96% of the pole spacing achieved by the HPS light in a single-sided layout with both products approaching 200-ft spacing. In a staggered layout, the BetaLED product can span close to 350 ft, while the HPS light can support spacing greater than 400 ft.

The report concluded that the BetaLED luminaire could offer lower life-cycle cost than the HPS light if the LED life was 50,000 hours (12 years) or more. Moreover the cost estimate assumed that the buyer would pay 50% of list cost based on a volume purchasing discount.

It will be interesting to see industry reaction from this second LRC report on street lights relative to RP-8 requirements. The report on collector-road lighting last fall generated significant controversy with some companies and even the DOE questioning the methodology behind the data.

The LRC is a part of the Rensselaer Polytechnic Institute (RPI). The LRC’s National Lighting Product Information Program (NLPIP) performed the street light research and published the specifier report.