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Demonstration Assessment of Light-Emitting Diode (LED) Roadway Lighting

Host Site: I-35W Bridge, Minneapolis, Minnesota

Final Report prepared in support of the U.S. DOE Solid State Lighting

Technology Demonstration GATEWAY Program

Study Participants:

Pacific Northwest National Laboratory U.S. Department of Energy

Minnesota Department of Transportation Federal Highways Administration BetaLED

August 2009

Prepared for the U.S. Department of Energy by Pacific Northwest National Laboratory

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PNNL- 18687

Demonstration Assessment of Light-Emitting Diode (LED) Roadway Lighting at the I-35W Bridge, Minneapolis, MN

Final Report prepared in support of the U.S. DOE Solid-State Lighting

GATEWAY Technology Demonstration Program

Study Participants:

Pacific Northwest National Laboratory U.S. Department of Energy

Minnesota Department of Transportation Federal Highways Administration BetaLED

B.R. Kinzey M.A. Myer

August 2009

Prepared for the U.S. Department of Energy under Contract DE-AC05-76RL01830

Pacific Northwest National Laboratory Richland, Washington 99352

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Electronic copies of the report are also available from the DOE Solid State Lighting website at .

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Preface

This report documents observations and results obtained from a lighting demonstration project conducted under the U.S. Department of Energy (DOE) Solid-State Lighting GATEWAY Technology Demonstration Program. GATEWAY supports demonstrations of high-performance solid-state lighting (SSL) products in order to develop empirical data and experience with in-field applications of this advanced lighting technology. The program focuses on providing independent, third-party data for use in decision-making by lighting users and professionals. Before being extrapolated for use at other sites, this data should be considered in context with other information relevant to the particular site and application under examination.

GATEWAY evaluates and reports on the field performance of SSL products. Each demonstration typically compares one SSL product against the incumbent or otherwise standard technology used in that location. Depending on available information and circumstances, the SSL product may also be compared to alternate lighting technologies; however, the purpose of the GATEWAY program is not to provide an evaluation of all possible alternatives for a given site and should instead be considered only as a single data point for the technology(ies) specifically considered. Manufacturers and users seeking demonstrations of non-SSL products should look to opportunities in the many demonstration programs run by electric utilities, and state- and regionally-funded energy efficiency programs.

Though products demonstrated in GATEWAY have been prescreened and tested to verify their actual performance, DOE does not endorse any commercial product or in any way guarantee that users will achieve the same results through use of these products. Readers considering use of the technologies evaluated in GATEWAY reports must conduct their own due diligence before making decisions regarding selection of any particular technology, or developing expectations of the results to be achieved thereby.

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iv

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Executive Summary

This report describes the process and results of a demonstration of solid-state lighting (SSL) technology conducted in 2009 at the recently reconstructed I-35W bridge in Minneapolis, MN. The project was supported under the U.S. Department of Energy (DOE) Solid-State Lighting GATEWAY Technology Demonstration Program. Other participants in the demonstration project included the Minnesota

Department of Transportation (Mn/DOT), Federal Highways Administration (FHWA), and BetaLED (a division of Ruud Lighting). Pacific Northwest National Laboratory (PNNL) conducted the measurements and analysis of the results.

The primary impetus for using LEDs in this particular bridge installation included the desire to

maximize reliability, minimize the need for periodic lighting maintenance (such as relamping the fixtures), provide adequate illumination across the considerable roadway width while avoiding excessive energy use, and complement the state-of-the-art technological design of the bridge itself. DOE has implemented a three-year evaluation of the LED luminaires in this installation in order to develop new longitudinal field data on LED performance in a challenging, real-world environment. This document provides information through the initial phase of the I-35W bridge project, up to and including the opening of the bridge to the public and the initial feedback received on the LED lighting installation from bridge users. A final project report will be issued at the conclusion of the three-year evaluation period, providing documentation of all performance, cost and maintenance data developed over that period.

Mn/DOT has taken a bold step in implementing LED luminaires in this high-risk, highly-visible

application when there is still a notable lack of field experience with the technology due to its still relatively recent introduction to general illumination applications. It is anticipated that the results from this project will continue to serve as reference for many similar future installations.

As the bridge represents new construction rather than retrofit of an existing system, the base or

reference case for purposes of comparison had to be estimated through lighting simulation. Issues remain as to the precision of the base case design that are essentially unanswerable short of pursuing installation of an actual system. Nevertheless, initial findings of the evaluation are favorable, particularly for a lighting technology that is still in a relatively early stage of development. Table ES1 indicates a minimum energy savings level of 13% for the LED installation relative to the simulated base case using 250W HPS “Mongoose” fixtures.1

Table ES1. Energy Calculation

1

Actual savings may be greater, depending on uncertainties with the baseline. See related discussion.

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Illumination levels produced by the LED lighting compare favorably against the base case HPS

installation. Table ES2 lists the actual measured values for the LED installation, along with modeled values for a conventional HPS installation. Note that, when installed in a fully horizontal or level orientation, the 250W HPS base case fails to meet Mn/DOT’s uniformity criterion (indicated by the shaded cell), and that a 15° upwards tilt from horizontal is necessary to provide sufficient illumination across the entire width of the bridge roadway. The GATEWAY program believes that such a configuration would not be acceptable from either a light pollution or driver glare perspective; however, to expedite the evaluation process this design (i.e., the energy that would be used by it) was accepted as the base case. What this assumption means for the associated energy savings estimate is uncertain—other than suggesting that the 13% value may be

conservative, and perhaps significantly so if higher wattage HPS luminaires would in fact be required to meet the project specifications.

Table ES2. Illuminance Levels on the Bridge for Day 1

1Requirements LED HPS (Level)

3Maximum – 1.97 fc 5.17 fc 4Max:Min – 7.58 34.47

115° Tilt2

4.77 fc 11.63

1. be applied to the modeled values as desired.

2. Modeled with a 15° luminaire tilt upwards from horizontal, in order for the 250W Mongoose simulation to

meet Mn/DOT illumination requirements across the bridge roadway width. 3. Mn/DOT desired results towards the higher end of this range ≈ 0.8 – 1.0

4. Though this wasn’t an absolute requirement, Mn/DOT desired more stringent uniformity ≈ 3:1.

The LED luminaires commanded a significant price premium, costing about $38,000 more than the HPS base case installation. Evaluating the investment for simple energy payback yields a lengthy payback period, given the relatively small energy savings level of 13% and low price of electricity that Mn/DOT pays for illuminating the bridge ($0.0674/kWh). The bridge contractor had offered to include the LED

luminaires as part of the construction package at no additional cost, however, so that Mn/DOT’s decision was primarily based on other issues.

One potentially significant benefit of the LEDs in this installation is avoiding rolling lane closures on the heavily-traveled interstate bridge for the purpose of relamping the HPS fixtures. Rolling lane closures involve multiple crew members and various maintenance and safety vehicles, diversion of traffic, as well as related administrative tasks (e.g., approvals, scheduling, etc.). Mn/DOT records show an average cost of relamping fixtures along interstate roadways of between $130-150 per pole. The required frequency of relamping is affected by a number of factors, including the specific lamps used, vibration levels of the bridge from traffic and wind, power quality, and others. The previous bridge saw a lamp mortality rate of approximately 50% every two years, though an upgrade to the lamp manufactured by EYE2 improved this somewhat, and the

2

Specification sheet included in Appendix A.

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new bridge construction has likely eliminated many of the vibration problems experienced in the previous design. Figure ES1 below illustrates the impact of various relamping cycle times on the simple payback calculation, from the assumed maximum of five years down to one year.

Figure ES1. Simple Payback of the LED System vs. Frequency of Relamping a Conventional HPS System on the

I-35W Bridge.

Finally, the project conducted a voluntary Web-based feedback survey of nearly 500 self-described bridge users, who had driven or been passengers across the bridge during the hours of illumination. Users expressed strong preference for the LED lighting, compared to the conventional lighting installed at both ends of the bridge. In the section of the survey allowing open comments by the participants, for example, positive comments outnumbered negative ones by about five-to-one. Section 4.0 contains the feedback survey results, and all comments are listed in Appendix E.

All lighting-related experiences and expenses on the bridge will continue to be monitored over the next three years, with a final follow-up report issued at project conclusion.

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viii

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Contents

Preface.................................................................................................................................................................................iii Executive Summary ...........................................................................................................................................................v 1.0 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 3.0 3.1 3.2 3.3 4.0 4.1 4.2 5.0

Introduction.......................................................................................................................................................1.1 Methodology......................................................................................................................................................2.1 Site Description............................................................................................................................................2.1 Standard Luminaires....................................................................................................................................2.2 New Luminaires...........................................................................................................................................2.4 Installation.....................................................................................................................................................2.4 Power and Energy........................................................................................................................................2.5 Illuminance....................................................................................................................................................2.5 Future Illuminance Measurements............................................................................................................2.7 Economics.........................................................................................................................................................3.1 Product Costs...............................................................................................................................................3.1 Maintenance..................................................................................................................................................3.1 Simple Payback.............................................................................................................................................3.4 User Feedback...................................................................................................................................................4.1 Lighting Expert Review Panel...................................................................................................................4.1 Driver Questionnaire...................................................................................................................................4.2 Discussion..........................................................................................................................................................5.1

Appendix A – Lamp, Ballast and Meter Information..............................................................................A.1 Appendix B – Luminaire Photometric Testing Results..........................................................................B.1 Appendix C – BUG Analysis of 250W Mongoose Fixture ....................................................................C.1 Appendix D – Summary Simulation Results of 250W and 400W Mongoose Luminaires ...............D.1 Appendix E – I-35W Bridge Survey Comments.......................................................................................E.1

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Figures

Figure 2.1. Luminaires installed on the I-35W bridge............................................................................................2.2 Figure 2.2. Aerial view of I-35W bridge...................................................................................................................2.7 Figure 3.1. Simple Payback of the LED System vs. Total Cost of Relamping a

Conventional HPS System.....................................................................................................................3.5

Tables

Table 2.1. Power Calculations for the Bridge Span...................................................................................................2.5 Table 2.2. Energy Calculation.......................................................................................................................................2.5 Table 2.3. Illuminance4 Levels on the Bridge for Day 1..........................................................................................2.6 Table 2.4. Measured Illuminance at Three Roadway Locations..............................................................................2.8 Table 3.1. Cost of Products for the I-35W Bridge....................................................................................................3.1 Table 3.2. Assumptions for Estimation of Maintenance Savings...........................................................................3.3 Table 3.3. Simple Economic Payback for I-35W Bridge for Different Relamping Cycles.................................3.4 Table 4.1. Responses from User Feedback Survey...................................................................................................4.3

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1.0 Introduction

This report describes the process and results of a demonstration of solid-state lighting (SSL) technology in a roadway lighting application conducted in 2009 in Minneapolis, MN. The project was supported under the U.S. Department of Energy (DOE) Solid-State Lighting Technology GATEWAY Demonstration Program. Other participants in the demonstration project included the Minnesota Department of

Transportation (Mn/DOT), Federal Highways Administration (FHWA), and BetaLED (a division of Ruud Lighting). Pacific Northwest National Laboratory (PNNL) conducted the measurements and analysis of the results. PNNL manages similar demonstrations for DOE and represents DOE’s perspective in the conduct of the work.

DOE supports such demonstration projects to develop real-world experience and data with SSL products in general illumination applications. DOE’s approach is to carefully match applications with suitable products and form teams to carry out the needed project work. Other project reports and related information are available via DOE’s SSL website at .

The recently-reconstructed I-35W Bridge in Minneapolis, MN was designed to showcase state-of-the-art technology in all respects. In keeping with this approach, Figg Engineering Group (Figg), the design firm, included LED roadway luminaires by BetaLED in their proposal for the bridge. As LED technology is still largely unproven for such a demanding and critical application, its potential use represented a bold departure from established practice, and hence introduced an element of risk to the bridge reconstruction project. For this reason a number of the staff involved expressed reservations with regard to use of LEDs, and Mn/DOT approached the GATEWAY program to provide independent analysis and evaluation of the proposed lighting design.

One of the first concerns expressed by Mn/DOT was that the LED product, upon initial review, appeared to fail to meet a relevant Mn/DOT energy requirement. 2008 Minnesota Statute 216C.19 states:

No new highway, street or parking lot lighting may be installed in violation of these rules. Existing lighting equipment, excluding roadway sign lighting, with lamps with initial

efficiencies less than 70 lumens per watt must be replaced when worn out with light sources using lamps with initial efficiencies of at least 70 lumens per watt.3

Minnesota’s statute focuses on the light source (in this case, the lamp) because its efficacy is easier to verify. The obvious intent of the statute is to increase the use of high-efficacy sources, but the statute neglects to also look at the other relevant characteristics of the lighting system. All of the system variables must be factored in to provide an accurate comparison of the two technologies (i.e., HPS vs LED).

The LED luminaires that were under consideration for this project possessed an efficacy of 65-67 lumens per watt (LPW), initially appearing as insufficient to meet the statute. LEDs are different in many respects from other lighting sources, however, and considering the other relevant system characteristics showed them to easily meet the intent (if not the letter) of the statute.

3

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In this case, conventional high-intensity discharge (HID) lamps typically offer initial efficacies well in excess of 70 LPW (source efficacy). However, the statute only focuses on the lamp and does not mention system (lamp + ballast) efficacy. HID ballasts typically have a ballast loss (power consumed by the ballast in addition to the lamp) between 10%-20% of the rated lamp wattage, reducing the efficacy of the system. By focusing solely on lamp efficacy, the statute also neglects fixture efficiency (the ratio of the light emitted by the luminaire relative to the light created by the source), typically between 65%-90% for roadway luminaires (in this particular case, 72.8%). Therefore, although the 250W HPS baseline lamp for this demonstration has an initial source efficacy of 111 LPW, when the power for the ballast and the fixture efficiency are factored into the application, the initial luminaire efficacy is reduced to 71 LPW [28,500 (initial lamp lumens) / 291W (Ballast Input Power) x 72.8% (fixture efficiency)].

Statutes are generally written around lamp efficacy because lamps are largely interchangeable and often have different efficacies. Ballast losses and fixture efficiencies can also vary greatly between products, thus a considerable range of overall luminaire efficacy is possible with conventional products depending on the specific configuration of a given luminaire. This situation contrasts with that of dedicated LED luminaires, which are photometrically measured as complete luminaires (light source [LED]+ driver + fixture), thus yielding a luminaire efficacy value from the outset. The LED luminaires in this demonstration offered

luminaire efficacies of 65 and 67 LPW (distribution type III and type V, respectively), much nearer that of the baseline 250W HPS system than might be initially perceived.

In addition, no consideration is given in the statute as to the distribution or use of the lumen output. Efficient production of lumens is of little value when those lumens are sent in directions they are not wanted or not useful. Over-lighted areas (hotspots) and light trespass represent wasted light, and consequently, wasted energy. In comparison with the standard HPS lighting product, the LED system more effectively lights the task plane and thus significantly reduces such associated inefficiencies.

In the end, the results of DOE’s illumination modeling showed that the LED product was more than adequate to meet the intent of the statute, which allowed the project team to move beyond this initial

concern. “Early adopters” of SSL technology will likely encounter these discrepancies with regulations, codes and design specifications based on traditional light sources until they are updated.

DOE’s initial concern regarding the original proposed lighting installation design was that there were no energy savings apparent from the use of LED luminaires. Subsequently, the project team determined that the proposed LED luminaires were slightly oversized. Through the use of modeling software, the project team fine-tuned the design and was able to reduce the size of most of the luminaires while still meeting all

Mn/DOT illumination requirements, to achieve an anticipated energy savings level of about 13% relative to the assumed 250W HPS baseline.

After this slight adjustment in the design, DOE agreed to participate in the demonstration, which also encouraged Mn/DOT to move forward with using the LED luminaires in the installation. Mn/DOT continued to express concerns about both the performance of the luminaires as well as their longevity, however. These and other characteristics of the LED system will continue to be monitored by the GATEWAY program over the planned three-year evaluation period.

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2.0 Methodology

Because the I-35W Bridge was a new construction project, the project team’s lighting design and

evaluation relied heavily on computer-aided design (CAD) and lighting simulation software (AGi 32). Only the main span of the bridge was to be lighted by LEDs, with the approaches and the remaining portion of the roadway lighted by conventional HPS luminaires. A site visit to the bridge was planned for the period between completion of construction and its public opening to verify that illumination levels would in fact meet Mn/DOT requirements.

2.1 Site Description

The new bridge is comprised of two separate spans 1215’ long, each containing five 12’ wide lanes with a 14’ inside shoulder and 13’ outside shoulder. The 87’ overall width is somewhat larger than typical for Mn/DOT specifications. This unusual width and other factors resulted in modifications to the standard design practice.

For example, the bridge was designed with open outside shoulders as a result of a popular vote by Minneapolis residents. Instead of standard concrete barriers, the bridge has open metal guardrails which allow drivers views of the city and the river below as they cross the bridge. The open guardrails prevented the pole for the luminaires from being placed on the outside of the span as would be typical. Rather, the poles/luminaires run along the gap between the two spans (See Figure 2.1).

Next, locations of signs at the ends of the bridge and a power line at one end impacted the lighting design. In order to avoid large shadows on the roadway, the poles needed to be spaced a sufficient distance from the signs while not interfering with the routing of the overhead power line. These requirements constrained the location of the poles on either end of the bridge. Structural and aesthetic issues also

influenced placement of the poles. Whereas the main span of the bridge is lighted by luminaires mounted back-to-back between the main spans of the bridge, the ends are lighted by luminaires located along the outside of the bridge.

Mn/DOT provided guidelines for their desired levels of illumination on the bridge that included an average of between 0.8 and 1.0 footcandles (fc) across the main span and an average-to-minimum uniformity ratio of between 3:1 - 4:1.

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Figure 2.1. Luminaires installed on the I-35W Bridge.

2.2 Standard Luminaires

Mn/DOT provides specific information in the Mn/DOT Roadway Lighting Design Manual about selecting luminaires when designing a roadway. 4 These guidelines include the following information:

For roadway configurations with two or three lanes in each direction, the most common equipment used is the following:

250-watt HPS cobra head style luminaire 40-foot pole

Spacing of the 40-foot poles is usually 240 to 250 feet, depending on the desired footcandle level and the number of lanes.

When lighting a roadway configuration with three or more lanes, the following is used:

A mixture of 40-foot poles and 49-foot poles can be used 40-foot poles should be used on the ramps and loops

4

Which can be viewed at

.