Conversion of Streetlights to Light-emitting Diode (LED) Type

doi:10.21203/rs.3.rs-5085635/v1

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Conversion of Streetlights to Light-emitting Diode (LED) Type

https://doi.org/10.21203/rs.3.rs-5085635/v1

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Due to the increasing need for energy conservation and improved outdoor experience, current streetlights require an upgrade to light emitting diode (LED) lighting. LEDs are well known for their better operating hours, brighter color temperature, and reduced energy consumption. According to the U.S. Energy Information Administration, lighting accounts for 17% of the energy consumption of commercial buildings [1]. Approximately 1–3% of the total electricity consumption comes from public street lighting and highway lighting globally [2]. There are several challenges associated with this large-scale transformation from high-pressure sodium (HPS) to light-emitting diode (LED) lights, starting with inaccurate or less information on the existing inventory, correct ownership determination, education on the use of LEDs, and financing/funding issues. In this paper, a methodology was presented to overcome the challenges of LED transformation. As a sample case based on the existing profile of high-pressure sodium (HPS), incandescent (INC), fluorescent (FL), metal halide (MH), and mercury vapor (MV) in the District of Columbia, energy conservation from the conversion of HPS to LED type was presented. Total energy savings and GHG reduction from this conversion yielded a positive outcome from large-scale replacements with LEDs. LED drivers are capable of withstand the stresses that streetlights are exposed to. However, additional considerations from a lighting equipment specifier to select drivers with more robust capacitors withstanding high heat and frequencies are needed. A simple evaluation of HPSs vs LEDs showed greater performance for lower-rated LED wattage luminaires.

Electrical Engineering

energy conservation

high-pressure sodium (HPS)

light emitting diode (LED)

This concept of providing energy-efficient lighting systems is predominant in building design in both new and retrofit projects. Both International Energy Conservation Codes and the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 90.1 mandate the need for energy-efficient lighting systems [3]. Lighting has evolved from incandescent bulbs, fluorescent materials, metal halides, high-pressure sodium, and mercury vapor to light-emitting diodes (LEDs).

Most applications for lighting include illuminating the interior and exterior areas of buildings. With minimum standards on average, uniformity, and veiling illuminance, designers tend to select suitable lumen packages for luminaires for a given application. For example, an indoor 36 W, 2’ x 4’ LED troffer offers up to 4000 lumens of output at a correlated color temperature (CCT) of 4000K. The criteria for CCT vary by type of application, as there are set standards for the acceptable range of CCT for a given application [4].

Indoor applications include illuminating office spaces, storages, electrical, IT, breakrooms, corridors, stairways, elevators, basements, and other room spaces. Similarly, outdoor applications include illuminating entrances, exits, building facades, parking garages, and lots. Street and roadway lighting is another primary outdoor application. According to the U.S. Energy Information Administration, lighting accounted for 6% of total energy consumption for residential (in 2020) and 17% for commercial (in 2018) applications in the U.S. [1]. Because of the significant contribution to energy consumption, the conversion of any non-LED type luminaires to LEDs becomes a viable choice when energy conservation is considered.

LEDs are known for their superior performance against conventional high-pressure sodium, mercury vapor, metal halide, mercury vapor, and fluorescent light. Some of the streetlights based on aesthetics are classified as colonials, period post tops, area, or flood types [5]. Some of these advantages include higher operational life, better light output, durability, and energy efficiency [5] [6]. The basic principle for semiconductors applies to LED lighting. The recombination of electrons and holes occurs at the depletion layer in a p-n junction semiconductor when forward biased [7]. Depending on the energy band gap (E_g), the amount of energy emitted in the form of light is determined. Figure 1 shows the characteristics of an LED and how an LED emits light when a battery is connected to diode terminals.

LED technology aligns with circadian rhythm, decreases headaches, reduces stress, and increases productivity [8]. A reduction in energy and environmental impacts are inherent to LEDs, and improved security makes them perfect candidates for outdoor application. Dimming of lighting based on ambiance for indoor applications is a known solution to saving energy [9]. However, during large-scale application of LEDs for street lighting, such an application has untapped potential. Although lighting design experts can specify outdoor luminaires that meet the required average illuminance and uniformity ratio, meeting exact requirements per standard with market-available products with a given lumen package luminaire results in little overillumination. Dimming technology in place allows streetlights to be configured to be dimmed to a level close to the standards.

With the increasing need for energy conservation by implementing energy-efficient lighting for both indoor and outdoor applications, this paper studies overall energy savings with large-scale adoption of LED lighting for street lighting applications. When the majority of the streets in the US continue to receive LED upgrades, there are a significant number of conventional luminaries that supposedly increase the energy demand. As per Eaton, there are approximately 45 to 55 million streetlights in the U.S., and a majority of them are either HPS or MH [10]. According to the District Department of Transportation and the US Federal Highway Administration, more than 75,000 streetlights on DCs will be modernized with LEDs [11]. With this move, a significant amount of energy reduction is anticipated, and this paper quantifies the energy savings with the replacement of an equivalent LED lamp for an existing HPS.

LED streetlights offer improved driver alertness because of the more comprehensive correlated color temperature range, thus offering better visibility than HPS lights. Like any other type of luminaire, LEDs start to degrade with time. The degradation analysis based on past research is given by equations (1) and (2):

1.1. LED degradation

The LED lighting output degradation is given by (1) [12]

$$\:\phi\:\:\left(t\right)=\left({\phi\:}_{0}-{\phi\:}_{e}\right).{e}^{-\alpha\:t}+\:{\phi\:}_{e}$$

where $\:\phi\:\:\left(t\right)$ is the luminous flux at a given time, $\:{\phi\:}_{0}$ is the initial luminous flux, $\:{\phi\:}_{e}$ is the end-of-life flux, $\:\alpha\:$ is the decay constant, and $\:t$ is the time. Similarly, it is also given by (2) [13]:

$$\:P\:\left(t\right)={P}_{o}{e}^{-\beta\:t}$$

where $\:P\:\left(t\right)$ is the light output at a given time $\:t$, $\:{P}_{o}$ is the initial light output, and $\:\:\beta\:$ is the degradation constant.

According to equations (1) and (2), the light output decreases exponentially with time. LEDs offer improved operational life in comparison to HPS lamps. The light loss factor (LLF) often accounts for the depreciation of light over time for light designers to account for design. The recommended LLF depends on the local codes and standards. However, for manufacturers, the objective is to provide products with low degradation over time. Lighting systems are often designed based on a recommended LLF ranging as low as 0.7 [14].

Table 1 shows the components of an LED luminaire and lists the life, weakest subcomponent, and countermeasures. The weakest part of the entire system is the LED drivers.

Table 1

Components
Component	Life Expectancy*	Weakest Subcomponent	Improvement Measures
LED Lamps	100,000 hours	Diode Connectors	Allow switching them off not required
Drivers	100,000 hours	Electrolytic Capacitor	Reduce abnormal on-offs
Internal Wires	20–30 years	Insulation	Reduce LED stress
Photocell	5–10 years	Electronic	Allow good contact
Casing/Fittings	30–50 years	Screws	Paint them
Lens	100,000 hours	Glass	Avoid Overheating
*Life expectancy is based on commercially available products

Table 2 shows the components of a voltage-controlled LED driver, wherein the major components comprise the power supply transformer and the rest are small electronic components.

Table 2

Voltage-controlled LED Drivers
Component	Purpose
Power Supply Transformer	Step Down to the required Voltage
Rectifier	Convert AC to DC
Voltage Regulator	Regulates to required Voltage
Inductor	Stores/Releases Energy
Capacitor	Filters both input and output
Feedback	Controls output
Protection Devices	For protection against surges and faults
Housing	Encloses together
Reflector	Reflects the light
Connectors	For connections

Normally, capacitors are major failure points in LED drivers [15]. This is due to high heat dissipation and operation at high frequencies. As an equipment buyer, one must look for LED drivers with high-quality capacitors. There are several types of drivers, either current or voltage controlled. There are specialized drivers, such as XVOLT by Acuity Brands, available on the market that can withstand poor power quality and offer applications for street lighting [16]. To study the performance of the HPS lamps against LED luminaires, the average illumination in the footcandles and the uniformity ratio were compared in the methods section. The performance of LEDs is better at a significantly lower wattage.

1.2. Concept of Energy-Efficient Street Lights

Solar Street Lighting with a local solar panel and battery pack mounted to a light pole offers reduced dependence on grid power. The reliability of this concept is questionable because of the risks of dirt and dust accumulation or shading due to overgrown vegetation. Dimming technology ensures that lights are dimmed to accommodate only the required illumination per local standards. Improving the streetlight by incorporating a minimum of LED replacement faces many challenges. A major challenge is preparing a replacement plan, which relies on the question of how recent the available inventory of streetlights was. Street light inventories are published for public use, but some jurisdictions have faced issues related to determining the ownership and responsible parties for the maintenance of the equipment [17]. For example, streetlights are either municipal, department of transportation, or utility owned but operated by themselves or by third parties.

1.2.1. LED Programs

In Maryland, 106,662 municipal streetlights out of a total of 354,352 were converted to LEDs as of 2019 [6]. In Virginia, 23,035 municipal streetlights out of a total of 741,039 were converted to LEDs as of 2019 [6]. The major challenges were related to a lack of education, inventory database, ownership details, financing options, and clear and transparent processes/cost structures for conversion [6]. New York achieved the goal of transforming 500,000 municipal streetlights into LEDs by partnering with more than 130 municipalities [18]. Kansas City plans for upgrades of 84,000 streetlights with LEDs and thus projects a total savings of $27 million by 10 years [19]. Along with the city of Auburn, Alabama Power replaced several streetlights with LEDs [5]. In the city of Phoenix, Arizona replaced 100,000 existing streetlights with LEDs [20]. Thus, improving participation in LED conversion is visible throughout the U.S.

2.1. Replacement Steps

The simple steps to allow a smooth transition to an LED are shown in Fig. 2. Inventory management is key to knowing the existing number of lights, technical specifications, and types of lights. It is crucial to know who the responsible parties are for the replacement based on ownership details (such as whether a municipality or utility owned). Once the responsible parties are determined, a preliminary assessment of LED replacement or retrofitting must be carried out. Then, the parties should be educated on the benefits of LED streetlights, and eventually, talks about available financing or funding opportunities should be initiated. The Department of Energy presents self-funding, utility financing, grants, rebates, and third-party financing. For instance, with the replacement of 3,750 lights with LEDs in Gaithersburg, MD was budgeted under Capital Improvement Funds [21]. Upon funding availability, detailed LED system designs with either replacement with LED luminaires or retrofitting must be carried out.

The street lighting design phase includes performing existing condition assessments. The existing conditions for the detailed design are listed in Table 3.

Table 3

Existing Conditions Checklist
Item	Field Data*
Location of Pole	Street Address
Pole Identification Number	12345
Owned By	Municipality
Maintained By	Municipality
Luminaire Number	15
Luminaire Type	HPS
Luminaire Wattage	250 W
Luminaire (Lamp) Condition	Fair
Voltage/Phase	277/480 V, 1 Phase
Pole Height	26 feet
Pole Type	Wooden
Pole Condition	Fair
Pole Spacing	60 feet
Luminaire Arm Length	4 feet
Lens Condition	Poor
Power Supplied From	Electrical Service A, Circuit 1
Size of Supply Conductors	2 #2 AWG & #6 AWG Ground
Location of Electrical Service	Street/Building Name
*Note: Field data are based on a general understanding of an existing lighting system

Existing conditions documentation is required for both planning and design. As an example, Fig. 3 shows an existing HPS lamp with minor corrosion to the housing, whereas Fig. 4 shows damaged lamps. Apart from documentation of the operational condition parameters mentioned in Table 1, a readily available database for public use becomes a valuable resource in the long term where both operations and maintenance are concerned. For example, DDOT maintains a publicly available GIS platform for all streetlights. Figure 5 is a schematic representation of the documentation of the location of the poles in map view along with the details from the Table 1 template.

The replacement type varies depending on the existing conditions. Some may require the replacement of defective pole structures with new LED luminaires, whereas many may require the replacement of existing non-LED types with LED-type luminaires. However, local standards may require upgrades to the electrical distribution system (especially overcurrent protection devices and conductors), as LEDs offer significant load wattage reduction. Additionally, pole spacings require re-evaluation when any of the standard parameters, such as uniformity ratios, are compromised with existing pole spacings.

Figure 6 shows a schematic diagram of the system of LED streetlights powered by a three-phase power source. The power conductors, overcurrent protection devices, and type of LED lamps are designed based on applicable standards within the local jurisdiction. For example, a 277/480 V, 3-phase system with three conductors of 8 AWGs and 10 AWGs will support 100 W LED lamps located within 150 feet of the power source. Photocell controls are attached independently to each LED light; therefore, switching is based on ambient lighting levels. Figure 7. shows a schematic diagram in which dimming controls were added. For example, when a similar system is provided with dimming control, either user-controlled or motion sensors, the level of lighting can be adjusted, which will reduce the power consumption when the dimming controller is set.

2.2. Impacts on human health

During the nighttime, the amount of artificial lighting that determines interference with the human circadian rhythm is the predominant factor [22]. Whereas indoor lights play a key role in ambient lighting levels, little is known about how streetlights interfere with circadian rhythm as they are located outdoors. However, light pollution from streetlights reduces the visibility of dark skies. Most people use curtains for windows to ensure enough darkness. However, reducing light trespass is another aspect of an effective street lighting system to ensure that there is no light pollution when shining on surfaces other than designated roadways. Melatonin is responsible for improving sleep performance in humans, but increased exposure to light results in melatonin suppression [23]. Additionally, increased correlated color temperature results in visual discomfort, and some individuals are photosensitive based on their eye color [24].

2.3. Comparison of Photometry Results

Based on the criteria for a straight continuous roadway section (Illuminating Engineering Society of North America RP-8), a comparison of the average illuminance and uniformity ratio can be performed using open-source simulation software for lighting analysis. For a roadway classified as a collector with low pedestrian conflict, the average illuminance required was considered to be 0.4 footcandles (fc), and the uniformity ratio was 4.0. Using commercially available luminaries for HPSs and their LED equivalents, a comparison was performed for 150-foot roadway sections. Figure 8 shows the layout of the cobra head luminaries mounted at 26 feet high. The 70 W LED with a Type IV distribution pattern average illuminance was 0.41 fc with a uniformity ratio of 1.97, whereas with the 150 W HPS, these values were 0.51 fc and 3.65, respectively. A comparison of LED lamp performance against HPS lamp performance with varying correlated color temperature was not considered because it becomes part of a subjective visual comfort level.

2.4. Replacement with LED for DC

Using the available street lighting GIS information from the DDOT website (as of July 2024) [25], all the existing non-LED light profiles were obtained. The total installed capacity of street lighting by type of lamp is presented in Fig. 9. These options were replaced with an equivalent LED option, as listed in Table 3; thus, their wattages were used to estimate total energy savings. Using a general rule of 12 hours of operation daily, a yearly operation duration of 4,380 hours was indicated. The energy savings were based on a given 4,380 hours of operation. The HPS replacement with LED is presented in Table 4.

Table 4

LED Equivalence Wattage of HPSs
HPS Luminaire Wattage (W)	*LED Luminaire Equivalent Wattage (W)	Rated Luminous Flux (Lumens)
70	55	6,300
100	84	9,500
150	130	15,800
175	125	14,400
200	150	22,000
250	200	29,000
400	300	50,000
1000	843	130,000
*Note: LED equivalence was based on market-available products

The annual energy consumption of existing HPS lights vs. replaced LED lights is presented in Fig. 9. Here, an annual energy consumption reduction of 12.12 GWh was obtained. As shown in Fig. 11, a majority of the HPS lights were rated at 250 W and 400 W, followed by 100 W, 150 W, and 70 W. A few lights were used: 175 W, 200 W, and 1000 W. The HPS lamps’ wattage typically ranged between 70 and 1000 W, and their replacement LED ranged between 55 and 843 W. According to the U.S. Energy Information Administration, 1 kWh of electricity produces 0.86 pounds of CO₂ emissions [26]. Thus, with a 12.12 GWh reduction in energy usage, a 5,213 US ton of CO₂ reduction is possible. The total cost of energy saved is $1.94 M at an assumed tariff of electricity of $0.16/kWh. Energy reduction, CO₂ reduction, and the cost of energy saved were obtained from equations (3), (4), and (5), respectively.

$$\:{E}_{annual}=\:\frac{{w}_{Lamp}\times\:\text{4,380}}{1000}$$

where $\:{E}_{annual}$is the annual energy consumption (in kWh) and $\:{w}_{Lamp}$is the lamp wattage (in watts).

$$\:{C}_{e}=\:u\:\times\:{E}_{annual}$$

where $\:{C}_{e}$ is the cost of electricity for the customer (in $) and $\:u$ is the cost of unit electricity ($/kWh).

$$\:{GHG}_{e}={E}_{annual}\:\times\:0.86$$

where $\:{GHG}_{e}$is the greenhouse gas emission in pounds of CO₂ equivalent.

Figure 10 shows that the annual energy consumption with existing HPS luminaires is 56.72 GWh, whereas it is 44.46 GWH with LED replacement. The equivalent annual GHG emission reduction was 5,213 US tons of CO₂. The equivalent annual cost savings for energy reduction were $1.94 M. Although the DDOT has already planned for the replacement of HPS lamps with LEDs, this paper presented equivalent energy savings because of this move. Grand Rapids invested approximately $10 M in the conversion of a total of 18,000 streetlights to LEDs [27]. Therefore, with the given cost approximation for the District of Columbia, at least $40 M will be needed. Additional consideration of whether providing dimming control to curb energy reduction with added cost is a feasible solution is a point for further study. As an equipment specifier, LED products with drivers capable of withstanding power quality issues were recommended.

As a challenging real-world situation, modeling an approach to initiating an LED improvement project was presented, starting with preparing an accurate inventory and documenting existing conditions to determine ownership, preliminary assessments, education of owners, and planning of financing/funding and detailed design. Special considerations were given to the selection of drivers and ensuring low light trespass from luminaires. Increased exposure to light during the nighttime affects the human circadian rhythm. Consolidation of large-scale LEDs when compromising the circadian rhythm requires evaluation. An approach to documenting existing conditions was presented. The use of available open-source lighting design software for the replacement of HPS lamps with LEDs indicated the superior performance of LED lights in terms of the average illuminance and uniformity ratio. Since HPSs composed a majority of the District of Columbia streetlights, the overall energy savings from LED replacement were 12.12 GWh, which equated to a 5,213 US ton of CO₂ reduction. The concept of implementing solar-powered streetlights offers a further reduction in energy demand. The selection of a suitable driver and its hardware becomes a choice for a buyer or lighting designer.

The failure rates of LEDs will start to improve as the technology starts to grow. With the given price, there will be a buyout between the types of components selected for LED drivers. With known failure points, there are excellent chances wherein cheaper-cost products are developed by avoiding such failures. As field conditions continue to let LED lamps and drivers burn out and dimming controllers fail, manufacturers can obtain excellent information from past experience for product improvement. Moreover, certain applications, such as light fidelity (Li-Fi), using streetlights might become popular and start offering better data connectivity than conventional Wi-Fi. Many applications of using LEDs for producing germicidal ultraviolet light (GUV) and their significant advancements in this technology help reduce viruses and bacterial growth in outdoor environments.

In the direction of sustainable futures, consideration of all three pillars—social, economic, and environmental factors associated with LED usage—must be considered. A reduction in energy demand by improving the lumen output at reduced wattage by improving with new materials does not add value unless it has any major positive social or economic impact. There will always be a buyout between the three pillars (social, economic, and environmental impacts) of sustainable development. Manufacturers to ensure sustainable development have become a topic of research.

As LED technology improves, there are possibilities for reducing blue light, essentially the harmful ultraviolet (UV) and infrared (IR) radiation to which human eyes are exposed. The human eye perceives colors based on this rendering, so the most suitable color rendering indices are used; thus, selecting the appropriate color rendering index (CRI) becomes a subject of subjective visual comfort. Artificial lighting has changed the way people lead their lives at night. Everyone has their own circadian rhythm. As people start to become aware of the effects of artificial lighting, more education on how LEDs interfere with the human circadian rhythm must be emphasized. The impact of artificial lighting on wildlife became another aspect of the study. For example, insects and bugs tend to be attracted to brighter lights. Like in humans, which have a circadian rhythm, sleep cycles occur in animals and birds and require further study.

Like interior lighting controls based on occupants, streetlights may go on-off or dim to a certain level when there is less pedestrian or road traffic. However, at the same time, considerations of public safety must be focused on reducing light levels during reduced occupancy. The large-scale adoption of LEDs and their controls requires study of both visual comfort and safety. The inherent advantage of being able to control lamps must be utilized because of their full potential, as LEDs continue to outweigh HPS lamps.

AC	Alternating Current
ASHRAE	American Society of Heating, Refrigerating and Air-Conditioning Engineers
CCT	Corelated Color Temperature
CRI	Color Rendering Index
DC	Direct Current
fc	footcandles
FL	Fluorescent
GGE	Gasoline Gallons Equivalent
GUV	Germicidal Ultraviolet
HPS	High Pressure Sodium
INC	Incandescent
IR	Infrared Radiation
LED	Light Emitting Diode
Lif-Fi	Light Fidelity
LLF	Light Loss Factor
MH	Metal Halide
MV	Mercury Vapor
UV	Ultraviolet
W	Watts

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The authors declare no competing interests.

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Conversion of Streetlights to Light-emitting Diode (LED) Type

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Abstract

Figures

1. Introduction

1.1. LED degradation

1.2. Concept of Energy-Efficient Street Lights

1.2.1. LED Programs

2. Methods

2.1. Replacement Steps

2.2. Impacts on human health

2.3. Comparison of Photometry Results

2.4. Replacement with LED for DC

3. Results

4. Conclusion

5. Future aspects

Abbreviations

References

Additional Declarations

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