Between February and March 2010, the National Lighting Product Information Program (NLPIP) at Rensselaer Polytechnic Institute’s Lighting Research Center purchased six streetlights identified by manufacturer representatives as equivalent to a 100-watt (W) high pressure sodium (HPS), Type II, medium, full cutoff cobra head. One used an HPS lamp (the base case model), one used an induction lamp, and four used light-emitting diode (LED) modules. NLPIP determined how many of each type of streetlight were needed to illuminate one mile (1.6 kilometer) of a local road in an urban residential area to meet the roadway lighting design criteria specified in the American National Standards Institute (ANSI)/Illuminating Engineering Society of North America (IESNA) RP-8-00, American National Standard Practice for Roadway Lighting (referred to as RP-8 below). NLPIP then calculated power demand and life-cycle costs per mile for each streetlight. For a more complete understanding of this application, additional analyses were conducted related to white light benefits, discomfort glare, absolute photometry, manufacturer-supplied photometric data, higher light output streetlights, higher mounting heights, wider roads, and volume discount pricing.
Using a GE Lighting 100 W HPS streetlight as the tested base case, NLPIP found that:
- The tested LED streetlights required 3% to 92% (average 40%) more poles per mile than the base case to meet the RP-8 design criteria. The tested GE Lighting induction streetlight required 64% more poles per mile than the base case to meet the RP-8 criteria. One tested LED streetlight, the Beta Lighting STR-LWY-2M-HT-04-C-UL-SV, was able to provide pole spacing similar to the base case.
- The tested LED streetlights required 41% less to 15% more power per mile than the base case (average 6% less per mile for a staggered layout and 24% less per mile for a single-sided layout) to meet the RP-8 criteria. The tested induction streetlight required 51% and 41% more power per mile than the base case in staggered and single-sided layouts, respectively, to meet the RP-8 criteria.
- The life-cycle costs per mile for all of the tested streetlights were dominated by the capital and installation cost of the poles and streetlights. The life-cycle costs per mile of the tested LED streetlights ranged from 0.98 to 2.84 times as much as the base case because of the pole spacing required by the tested LED and induction streetlights to meet RP-8. For an assumed LED module replacement interval of 25,000 hours, the average tested LED streetlight life-cycle cost per mile was 1.9 times that of the base case. For an assumed LED module replacement interval of 50,000 hours, the average tested LED streetlight life-cycle cost per mile was 1.6 times that of the base case. The average life-cycle cost per mile of the tested induction streetlight was 1.8 times that of the base case.
- NLPIP identified one tested LED streetlight that met RP-8 and could have a lower life-cycle cost per mile than the base case in one scenario largely because its pole spacing was close to that of the base case, and therefore, had a similar pole cost. With a volume discount of 50% for the streetlights and replacement modules (and lamps for the base case), the tested Beta Lighting STR-LWY-2M-HT-04-C-UL-SV streetlight in a single-sided layout would have a lower life-cycle cost per mile than the base case if it were to have a life of 50,000 hours (12 years) or longer (or at single-unit pricing, 113,000 hours [27 years] or longer).
- Some streetlight system owners may be able to obtain financial incentives for installing LED and induction streetlights. In order for the tested LED (with a life of 25,000 hours or longer) or induction streetlight systems to have a lower life-cycle cost per mile than the base case, the required incentives would have to range from $250 to $1,550 per streetlight, in addition to a volume pricing discount.
- At the RP-8 local road illuminance levels, additional power reductions of up to 15% were possible for the LED and induction streetlights under the CIE model of mesopic photometry. These power reductions would not change the rank ordering of the streetlights based on the life-cycle cost results.
- In addition to the streetlights tested for this study, NLPIP analyzed streetlights with higher light output offered on the manufacturers’ websites in November 2010 to determine if they could have the same pole spacing provided by the base case and meet RP-8 criteria. Since the LED streetlights with higher light output were limited by RP-8’s uniformity and disability glare ratio criteria, none of these streetlights were able to have the same pole spacing as the base case at a 25-foot (7.6-meter) mounting height.
These results are for the streetlights evaluated in this study, for the roadway and mounting height geometries used in the analyses, and for streetlight systems that meet the RP-8 lighting design criteria. Surveys of municipality and utility representatives, and outdoor lighting specifiers and manufacturers, by Mara et al. (2005) showed that, on average, only 25% of local roads are continuously lit as recommended by RP-8. Although 75% of streetlight system owners do not light their local roads to RP-8 recommendations, NLPIP followed the RP-8 performance criteria because no other national lighting standard exists, and because there is high variability in the pole spacings prescribed by municipalities. The low adoption rate of RP-8 nationally could indicate that this national standard is not meeting the needs of streetlight system owners.