R ESPONSE TO THE I LLUMINATING E NGINEERING S OCIETY
R EQUEST FOR P ROPOSAL
S UBMITTED :
N OVEMBER 4, 2013
P ROPOSING A GENCY :
V IRGINIA P OLYTECHNIC I NSTITUTE AND S TATE U NIVERSITY
O
FFICE OF
S
PONSORED
P
ROGRAMS
N ORTH E ND C ENTER
300 T URNER S TREET , S UITE 4200
B LACKSBURG , VA 24061

Approximately 50 percent of all motor-vehicle fatalities occur during nighttime driving, while only 25 percent of travel occurs at night (Griffiths, 1994; Janoff et al. 1986; ANSI-IESNA RP-8, 2000). Roadway lighting provides drivers with the visibility needed to detect changes in roadway geometry, obstacles on or near the roadway, and pedestrians or other objects that enter the roadway. Studies have credited roadway lighting with lowering accident rates by 20 to 30 percent (Hasson and Lutkevich, 2002). LED
(Light Emitting Diode) lighting offers promises to further improve roadway safety and reduce power consumption due to the improved correlated color temperature availability. The whiter (cooler) color of
LED lighting and improved uniformity enables minimum luminance values to be achieved with lower lamp output while improving detection distance and thus improving safety. As a result, standards are being revised (such as RP-8-00) to include guidance for LED lighting. To fully appreciate the improved power usage and improved lighting quality, careful lifetime performance needs to be performed to ensure that the minimum lighting levels are met by the LEDs at the end of life (EOL) of the luminaires. This includes accounting accurately for light loss factors (LLF) such as luminaire dirt depreciation (LDD) which is not fully understood with respect to the wide variety of LED luminaires available for roadway lighting. This proposal will address the need for improved LDD factors for LED lighting.
The Virginia Tech Transportation Institute (VTTI) is pleased to respond to the IES (Illuminating
Engineering Society) Research Committee Request for Proposal (RFP) concerning the study and analysis of dirt depreciation on LED street lights. Leading the VTTI team as Principal Investigator (PI) and Project
Manager is Dr. Ronald Gibbons, Director of the Center for Infrastructure-Based Safety Systems (CIBSS).
For the past nine years, Dr. Gibbons has conducted multiple studies investigating safety systems that are constructed in the roadway infrastructure. In particular, he has focused on lighting and visibility in the roadway environment, especially concerning LED illumination. He has completed projects that consider the lighting requirements of pedestrians in mid-block crosswalks, the development of a model of visual behavior of a driver, and is currently PI of an FHWA-sponsored project that considers the spectral effects of a light source in the roadway environment and strategic efforts that evaluate use of lower light levels on roadways.
Based on the qualifications of the team that has been established, VTTI encompasses a significant skill set that will enable a response to all of the needs of the IES Research Committee during this project. VTTI’s team is also uniquely qualified for this project as they are currently testing a variety of luminaire types in a controlled environment.
Evaluation of VTTI Team against Proposal Evaluation Factors
1. Demonstrated
Technical
Expertise on the
Subject
The Project Manager, Dr. Gibbons, has managed more than $10 million in research at VTTI. Dr. Gibbons has performed research in the areas of roadway lighting and visibility for more than 20 years. He has investigated the impact of spectrum on roadway lighting, developed guidelines for midblock crosswalk lighting, and he is currently investigating the application of adaptive lighting systems to the roadway environment. Jason Meyer has developed instrumentation such as a luminance camera and a color camera and has performed photometric evaluations of lighting systems for D.C. and the Virginia Department of Transportation (VDOT); Matthew Palmer has developed fog measurement and robotic illuminance instruments as

Luminaire Dirt Depreciation from LED Luminaires VTTI
2.
3. Clear Proposal for
Research Methods
4.
Demonstrated
Understanding of the Problem
Resources to
Complete the
Project in a
Timely Manner within Budget well as harsh environment optical instrumentation and has 13 years of experience leading government R&D projects; and Travis Terry has performed significant photometric evaluations of lighting systems in Iowa,
Virginia, and Seattle, Wash. and is currently responsible for all lighting evaluations for the FWHA-sponsored study of roadway lighting for the
Adaptive Lighting Project.
VTTI is uniquely suited for this project as it is currently evaluating luminaire depreciation for a variety of projects. These projects include the measurement of light depreciation from luminaires both in-situ and in a laboratory setting. In fact, VTTI currently has complete control of two test locations, the Virginia Smart Road and a parking lot in Woodbridge, Va.
VTTI has complete records regarding the luminaire performance at installation and has monitored these locations for an extensive period of time. VTTI has also developed a sophisticated measurement system to perform the required data collection.
The methods we propose include an extensive evaluation of the dirt depreciation in a luminaire using the VTTI-developed RLMMS system.
This approach is unique; however, it minimizes manipulation of the luminaire while providing a superior stream of available data.
The project team has the available capacity. The team capacity allotted to this project and other commitments of the team are provided within this response.
Background
With the advent of any new light sources, the performance over time is critical to meeting the cost savings and performance predictions used to justify replacement of existing technology. Whether the source performance degrades as part of the wear and tear from the use of the system or whether it degrades due to dirt (and salt spray) and/or maintenance factors these must be accurately accounted for in the lighting design in order to meet the energy reduction goals while maintaining or improving roadway safety.
In the current lighting design approach, the dirt depreciation is applied as a component of the Light Loss
Factor (LLF) for the lighting design. This value is applied as a multiplier to achieve the maintained lighting level from the initial installed level. From ANSI/IES RP-8-00, American National Standard
Practice for Roadway Lighting:
LLF = LLD x LDD x LATF x LCD x HE x VE X BF
Where LLD is lamp lumen depreciation, LDD = Luminaire dirt depreciation, LATF is Luminaire ambient temperature affects, LCD = Luminaire component depreciation and also includes some optional factors such as voltage, transients, ballast factors, and heat extraction factors.
Of these, LLD is fixed by the lamp type (0.70 for LED). LATF is based on ambient temperatures and is usually 1.0 for most installations. LDD, however, can be quite low considering the installation environment as shown in Figure 1.
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Luminaire Dirt Depreciation from LED Luminaires VTTI
Figure 1: Luminaire Dirt Depreciation factors based on time and environment (ANSI/IES, 2005)
As all lighting designs are based on maintained lighting level, the LLF has a significant impact on the initial design. If the light loss factor from one design to another differs by 5 percent, the design with the higher light loss factor would require 5 percent more initial equipment, 5 percent more energy to operate, and 5 percent more maintenance. This means that the light loss factor and therefore the LDD factor has a significant impact on the overall cost of the project, which can mean the difference between new technology insertion or continued use of legacy systems at higher energy costs.
One of the shortcomings of the existing luminaire dirt depreciation factor is that it is assumed to be an equivalent multiplier across the luminaire output. However, this is not the case. In a small investigation using an HPS luminaire from the Virginia Smart Road operated by VTTI, a 400 Watt High Pressure
Sodium luminaire was removed from the road and photometered, then cleaned and photometered again.
The results (shown in Figure 2) indicate that the dirt depreciation is actually more significant in the extents of the light distribution than in the areas located more centrally under the luminaire. This makes sense, however, the tested luminaire was a flat lensed type II medium throw luminaire. For this distribution, there is a significant portion of the distribution that is projected at low angles through the edge of the glass. These low angles would be more significantly impacted by the dirt on the lens, and as such the throw of the luminaire would be diminished more than the central area. These results indicate that the application of a single factor for dirt depreciation is fundamentally incorrect.
One of the primary aspects of the LED luminaire in terms of dirt depreciation is that the optical components of an LED luminaire vary significantly from one luminaire design to another. Some luminaires are more traditional with the light sources and reflectors behind a glass panel whereas others use internal reflection to direct the light in a given direction and finally some aim the LED in the direction of the light distribution. Other variations include individual lenses for each LED which may or may not be behind another optical element sealed from dirt depreciation. Additionally, some optical elements may include many small prisms built into the outer surface to spread out the source of the light to reduce glare.
All of these light distribution features can cause dirt (and salt from spray) to accumulate at different rates.
Therefore, the impact of the dirt depreciation can vary depending upon the luminaire type. As a result, the
LDD is a significant topic for study with many variables to consider.
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Luminaire Dirt Depreciation from LED Luminaires VTTI
Figure 2: Photometric Dirt Depreciation Polar Distribution Showing Non-Uniform Luminaire Dirt
Depreciation
There is also an interesting possible outcome of this project which is a specification for cleaning a luminaire. Typically, a luminaire is maintained when the lamp is changed. Once the lens is open to access the lamp cavity, it is typically wiped with a rag before closing. As one might expect, the quality of the wiping, the cleanliness of the rag and the level of care varies by the maintenance worker. As a result, it is not likely that the maintenance of a luminaire will return it to a “like-new” condition. For LED luminaires, some are advertised as self-cleaning (which might require precipitation or water spray to activate) whereas others may be subjected to a similar cleaning method as the HID systems. By evaluating different cleaning approaches to the luminaire, it is possible to develop a specification for the maintenance of various types of LED luminaires.
Objective
The primary objective of this research is to establish the performance of various types of LED luminaires in terms of dirt depreciation. This performance will be established for various:
• luminaire optics types
• material types
• environment types
• luminaire IP ratings
A secondary outcome of this research may be a specification for the cleaning of LED luminaires.
Approach
Our approach to this project is slightly different than that specified in the RFP. We propose to use the
VTTI owned Roadway Lighting Mobile Measurement System (RLMMS) to measure the illuminance from the luminaires in-situ, then after cleaning the luminaires as would be performed in a maintenance operation, the luminaires would then measure the illuminance again. The RLMMS system is a unique
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Luminaire Dirt Depreciation from LED Luminaires VTTI data collection system that captures dense, accurate photometric data from a moving vehicle. Horizontal illuminance, vertical illuminance (glare), as well as roadway luminance are all collected along with corrected color temperature (CCT), and by nature of the measurement, the continuous variation
(uniformity) of the lighting.
The benefits of this approach are:
• The luminaires are not disturbed from their operating position thus reducing the potential to change the dirt distribution. This also minimizes risk to the roadway users by ensuring no luminaires are missing during nighttime driving. This also means there is no material handling requirements for the project;
• Multiple luminaires are measured rather than just one for each combination of parameters. The
RLMMS would measure the entire segment of a roadway rather than just a single luminaire in a goniophotometer. This allows for an evaluation of all of the metrics of the roadway including uniformity, glare and luminance. This will increase the statistical significance of the results as well;
• Luminaires on any public roadway, parking lot, etc. can be tested;
•
Permission to clean the luminaires will likely be much easier to acquire than permission to remove the luminaire for photometry;
•
A goniometer laboratory is not required, reducing project costs;
•
It provides for easy separation of some of the variables. Dirt deprecation (and salt) effects will be directly separated from other light depreciation factors – LLD and optical component effects. In addition, since the team will need to clean luminaires, the interior of luminaire can be checked for dirt ingress, and yellowing of some of the optics can be checked with a spectral transmission measurement; and
• Cleaning method efficacy will be determined as an added benefit of the study.
A previous example of a similar evaluation of LED luminaires is the work conducted as part of the U.S.
Department of Energy (DOE) Solid-State Lighting Technology GATEWAY Demonstration Program at the I-35W bridge location in Minneapolis, Minn. This was a demonstration of solid-state lighting (SSL) technology in a roadway lighting application conducted in 2009 in Minneapolis, Minn. With the reconstruction of the I-35W Bridge, LED luminaires were installed in order to investigate the efficacy as well as the efficiency of 20 LED luminaires over the course of three years. The proposed team assisted in the data collection utilizing the first prototype of the RLMMS system.
Test Sites
The potential test sites for this evaluation will be carefully chosen. Two of the test sites  the Virginia
Smart Road and the parking facility in Woodbridge  are a result of on-going work already underway at
VTTI. The other test sites will be selected based on the need to complete the range of luminaire types required for the study.
Virginia Smart Road, Blacksburg, Va.
The Smart Road is a controlled test bed designed for multiple lighting configurations and evaluations as well as other safety research. The road is built to Virginia Department of Transportation (VDOT) and
Federal Highway Administration (FHWA) standards. The Smart Road has a large number of features and capabilities and is highly adaptable. Included is a variable lighting test bed consisting of 38 overhead light poles that span a 1.1-mile section of the road. Fourteen luminaire poles, each installed with two
LED luminaires, are included in the test bed location. These luminaires will already have been installed for more than 24 months by the time the activities described in the current proposal will be conducted.
The luminaires in use at the Smart Road are shown in Table 1.
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Luminaire Dirt Depreciation from LED Luminaires VTTI
Table 1. Selection of Smart Road Luminaires
Manufacturer
Optical
Material
Optical Characteristics Ingress Protection (IP) Rating
Beta Acrylic
Molded lenses encasing each
LED within individual optics
N/A
Park-and-Ride, Woodbridge, Va.
Completed in September 2012, the Park-and-Ride location in Woodbridge, Va. features 25 luminaires provided by multiple manufacturers for the ongoing evaluation VTTI is conducting with VDOT. The luminaires were installed at the Park-and-Ride location following a laboratory evaluation at VTTI. Over the course of 24 months, the luminaires are inspected in terms of dirt buildup, luminaire temperature fluctuations, and CCT. Every three months, illuminance is measured horizontally at ground level, as well as vertically at a 1.5m height on 12x36 meter grids below the luminaires. Monitoring changes in the luminaire performance every three months is also accomplished through use of the VTTI-developed
RLMMS.
With these luminaires already installed in a location prone to dirt buildup through ongoing construction in the proximity, they will have been accumulating dirt for 24 months by the time the activities described in the current proposal will be conducted. This study will be completed by removal of the luminaires, which will be retested photometrically in the VTTI laboratory prior to cleaning and after.
Luminaires at the Woodbridge site that satisfy multiple categories indicated in the proposal request are listed in Table 2.
Table 2. Selection of Woodbridge luminaires
Manufacturer
Dialight
Philips
Lighting
Science
GE
Optical
Material
Optical Characteristics
Glass Flat lenses enclosing one or more LEDs
Glass Flat lenses enclosing one or more LEDs
Acrylic
Molded lenses encasing each LED within individual optics
Glass Flat lenses enclosing one or more LEDs
Ingress Protection (IP) Rating
6X
6X
6X
6X
Cree
Acrylic Molded lenses encasing each LED within individual optics
6X
Preliminary results of the performance of five different manufacturer LED luminaires are shown in Figure
3. The LEDs (luminaires “A” through “E”) are evaluated every three months, along with a high pressure sodium (HPS) luminaire (luminaire “F”). With corrections made for changes in ambient temperature, preliminary results indicate a slow decline in performance in some of the LED luminaires (such as luminaires “A”, “C”, and “E”).
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Luminaire Dirt Depreciation from LED Luminaires VTTI
Figure 3: Horizontal Illuminance Results
What is interesting to note is the steady increase in performance of the HPS luminaire (luminaire “F”).
While the dirt buildup on the luminaire lens has been observed to increase as time progresses, an explanation for the increase in horizontal illuminance can be attributed to how the dirt is distributed on the lens itself.
The project has an agreement with VDOT to test a variety of in-situ cleaning methods can be used and evaluated for this project.
Other Locations
The requirements of the RFP include multiple luminaire types to be measured and analyzed. The test sites will be selected to fulfill the requirements for the other luminaire types. The project team has extensive contacts in the industry to provide the required sites. These contacts, in both Cree and Parsons
Brinkerhoff, have committed to providing access to sites as required. Other locations under consideration include: o
Anchorage, Alaska both LED Commercial and Residential Lighting systems previously tested by VTTI o
Charleston, West Virginia – The project team has a commitment from the WV DOT to utilize their test area for our project. This test areas include 5 different luminaires on I-77 and 4.5 miles of luminaires on WV 61. o
Boston, Massachusetts Commercial Luminaires o
Cambridge, Massachusetts LED Commercial Luminaires
Analysis Methods
Using methods similar to the Woodbridge project, the VTTI team will use a combination of custom automated data analysis software combined with other analysis techniques optimized for the RLMMS system. The parameter of specific interest will be the performance change between a just cleaned luminaire and a dirty luminaire. This will be expressed as a ratio. Horizontal illuminance depreciation will be characterized at multiple locations relative to the luminaire position to obtain the distribution of the dirt
(salt) impact as well as the overall magnitude of the dirt depreciation. Direct separation of dirt depreciation from the other factors will enable easier data analysis and high statistical significance. The statistics of the other parameters will be analyzed as well as the significance. It is anticipated that the impact will be high due to the larger number of luminaires that can be tested with this approach

as opposed to removing and testing in a goniometer lab.
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