Web-Based Training for FHWA Roadway Lighting Workshop

Module 2: Lighting Hardware and Light Source 

Considerations for Roadway Lighting
Web-Based Training for FHWA Roadway Lighting 

Workshop 

Participant Workbook 

Module 2: Lighting Hardware and Light Source 

Considerations for Roadway Lighting 

(Other modules include: 

Module 1: Roadway Lighting Design Overview 

Module 3: Street and Roadway Lighting Design 

Module 4: Other Roadway Lighting Topics) 

May 2018 
NOTICE 

This document is disseminated under the sponsorship of the U.S. Department of 

Transportation in the interest of information exchange. The United States Government 

assumes no liability for its contents or the use thereof. This Report does not constitute a 

standard, specification, or regulation. 

The contents of this Report reflect the views of the contractor, who is responsible for the 

accuracy of the data presented herein. The contents do not necessarily reflect the official 

policy of the U.S. Department of Transportation. 

The United States Government does not endorse products or manufacturers named 

herein. Trade or manufacturers’ names appear herein solely because they are considered 

essential to the object of this report. 

QUALITY ASSURANCE STATEMENT 

The Federal Highway Administration (FHWA) provides high-quality information to serve 

Government, industry, and the public in a manner that promotes public understanding. 

Standards and policies are used to ensure and maximize the quality, objectivity, utility, and 

integrity of its information. FHWA periodically reviews quality issues and adjusts its 

programs and processes to ensure continuous quality improvement. 
TECHNICAL REPORT DOCUMENTATION PAGE 

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 

FHWA-SA-18-034 

4. Title and Subtitle 5. Report Date 

Web-Based Training for FHWA Roadway Lighting Workshop 

Module 2: Lighting Hardware and Light Source Considerations for May 2018 

Roadway Lighting 6. Performing Organization Code 

7. Author(s) 8. Performing Organization Report No. 

Daniel C. Frering, John D. Bullough, Kevin Chiang, Leverson Boodlal 

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) 

KLS Lighting Research Center, 11. Contract or Grant No. 

Engineering, Rensselaer Polytechnic 

LLC (Prime), Institute (Subcontractor), 21 DTFH6116D00017, TOPR No. 16-16 

45155 Research Union Street, Troy, NY 12180 

Pl, Suite 200, 

Ashburn, VA 

20147 

12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered 

Federal Highway Administration Report (2016-2018) 

Office of Safety 

1200 New Jersey Ave. SE 14. Sponsoring Agency Code 

Washington, DC 20590 

FHWA 

15. Supplementary Notes 

Joseph Cheung from FHWA served as the Project Manager. Cathy Satterfield, George Merritt, Michelle Arnold and 

Wilmari Valentin Medina from FHWA provided helpful technical comments. 

16. Abstract 

This document serves as a participant workbook for Web-Based Training for FHWA Roadway Lighting Workshop, 

Module 2: Lighting Hardware and Light Source Considerations for Roadway Lighting. Module 2 covers light 

sources, roadway luminaire classifications, luminaire poles, and lighting controls. Other modules include Module 

1: Roadway Lighting Design Overview, Module 3: Street and Roadway Lighting Design, and Module 4: Other 

Roadway Lighting Topics. 

17. Key Words 18. Distribution Statement 

No restrictions Roadway lighting, safety, visibility, crash avoidance

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price 

Unclassified Unclassified 89 

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
List of Acronyms and Abbreviations

AASHTO American Association of State Highway and Transportation Officials 

AlInGaP Aluminum indium gallium phosphide 

ANSI American National Standards Institute 

APL Advanced plasma lighting 

BUG Backlight-uplight-glare 

CCT Correlated color temperature 

cd/m2 Candela per square meter 

CRI Color rendering index 

DC Direct current 

DOE Department of Energy 

EMI Electromagnetic interference 

EPA Environmental Protection Agency 

HEP High efficiency plasma 

HID High intensity discharge 

HPS High pressure sodium 

IES Illuminating Engineering Society 

InGaN Indium gallium nitride 

K Kelvin 

L70 70% lumen maintenance 

lm lumen 

LED Light emitting diode 

LEP Light emitting plasma 

LPS Low pressure sodium 

LRC Lighting Research Center 

MH Metal halide 

MPH Miles per hour 

MV Mercury vapor 

PC Phosphor converted 

PIR Passive infrared 

RF Radio frequency 

RP Recommended practice 

W Watt 
Module 2: Lighting Hardware and Light Source Considerations for Roadway 

Lighting 

Roadway Lighting Design Overview 

Module 2, Slide 1 

This section of the Participant Workbook will help you review the content for Module 2, 

entitled "Lighting Hardware and Light Source Considerations for Roadway Lighting." 

The top of each workbook slide will indicate the module slide title and slide number in 

order to help you locate content within the workbook that matches content in the online 

modules. 
Navigating This Course 

Module 2, Slide 2 

This slide in the online module describes how to navigate through the course module. It 

is similar to the instructions in this workbook. 
Course Objectives 

Module 2, Slide 3 

Following completion of this module, the user will be able to accomplish the following 

objectives: 

 Select characteristics of roadway light sources 

 Evaluate luminaires based on luminaire classifications 

 Identify appropriate mounting hardware and equipment 

 Determine when adaptive lighting control is appropriate and quantify its benefits 
Table of Contents 

Module 2, Slide 4

Section 1: Light Sources - high pressure sodium (HPS), mercury vapor (MV), low 

pressure sodium (LPS), metal halide (MH), plasma, induction, light emitting diodes 

(LEDs) 

Section 2: Roadway Luminaire Classifications - luminaire classification system 

“BUG” rating, luminaire light distribution classifications, luminaire shapes and sizes, 

luminaire design considerations 

Section 3: Luminaire Poles - pole types, pole design, breakaway devices 

Section 4: Lighting Controls - photosensors, time clocks, occupancy sensors, 

networked control systems, adaptive roadway lighting 
Lamps and Light Sources 

Module 2, Slide 5 

A high intensity discharge (HID) lamp.

Commonly known as "light bulbs," electric light sources are called "lamps" in the lighting 

profession. The word lamp is a generic term for a manufactured light source device that 

converts electric energy into light. To simplify the discussion of lamps, it is common 

practice to group types that share operating characteristics. This has been done here. 

This course section will discuss several characteristics that should be considered when 

selecting the best lamp for a particular application. These characteristics include color, 

distribution, light output, efficacy, and life. For older technologies, such as high intensity 

discharge (HID) lamps, information will also be provided on the types of light sources 

that can be used to replace these technologies, and issues to consider when making a 

replacement. 

In this section we will discuss only those light source types commonly used in roadway 

lighting. 
High Intensity Discharge (HID) and Low Pressure Sodium Lamps 

Module 2, Slide 6 

High wattage HID lamps are often used to light parking lots and roadways due to their 

high lumen output and efficacy. 

Introduction 

The family of lamps known as high intensity discharge (HID) generally has higher light 

output (lumens) than incandescent, fluorescent, and other light sources typically used in 

building interiors. HID lamps are most often used in street lighting, parking lots, and 

other outdoor lighting applications. 

There are four basic types of lamps covered in this section: metal halide, high pressure 

sodium, mercury vapor, and low pressure sodium. Low pressure sodium lamps 

technically do not qualify as HID sources due to their low vapor pressure. However, 

because of their similarity to HID lamps in operation and application, they are included 

in this discussion. 

Metal halide and high pressure sodium lamps are covered with greater emphasis here 

than mercury vapor or low pressure sodium lamps because they are used in many more 

roadway applications. 
General Operation of HID Lamps 

Module 2, Slide 7 

HID and low pressure sodium lamps produce light by an electric discharge between two 

electrodes through a small vapor-filled chamber called an 'arc tube.' The chemical 

composition of these vapors determines the characteristics of the lamp, such as its 

color, life, and efficacy. The table above lists different HID lamps and the chemical 

composition they utilize to generate light. 

HID and low pressure sodium sources require a ballast to operate. The ballast supplies 

the high initial voltage necessary to start the electric discharge between the electrodes 

and the subsequent chemical reactions inside the arc tube. Because of these chemical 

reactions, HID lamps often need time to warm up in order to reach full light output. This 

starting period varies between the different lamp technologies; typically, it takes several 

minutes. Once the lamp has started, the ballast regulates the supply voltage for its 

proper operation.
High Pressure Sodium (HPS) Lamps 

Module 2, Slide 8

A roadway lighted with HPS streetlights. Notice the “golden-yellow” color of the light.

Because of their long life and high efficacy, high pressure sodium lamps are the most 

commonly used HID light sources for exterior applications such as streets, roadways, 

and security lighting. These lamps are easily distinguished from other HID sources due 

to the golden-yellow appearance of the light they produce. The color rendering 

capabilities of most high pressure sodium lamps are generally low compared to other 

available light sources. 
HPS Lamp Operation 

Module 2, Slide 9 

The yellow "mouse-over" circles in the diagram above (from top to bottom) refer to the 

following lamp components: 

 Outer Bulb – Hard glass that protects the arc tube. 

 Electrode (1) – Double coiled tungsten coated with emissive materials are 

located at each end of the arc tube. 

 Arc Tube – Translucent ceramic structure suitable to withstand thermal 

shocks caused by enclosed xenon gas, mercury, and sodium vapor. 

 Vacuum – The outer bulb is evacuated to prevent chemical degradation of 

the metal parts of the arc tube and to maintain the appropriate arc tube 

temperature. 

 Electrode (2) – Double coiled tungsten coated with emissive materials are 

located at each end of the arc tube. 

 Base – Several different types used to connect the lamp to the electric circuit 

and to support the lamp in the lamp holder. The most common types are 

mogul and medium screw base. 

HPS lamps produce light by an electric discharge through combined vapors of mercury 

and sodium, with the sodium radiation dominating the color appearance. These gases 

are contained within the arc tube of the lamp under high pressure. The arc tube in turn, 

is surrounded by an outer hard-glass bulb. The arc tube material most widely used is a 

translucent ceramic material. 

On either end of the cylindrical arc tube, tungsten electrodes are held in place with a 

sealing ceramic. When the ballast sends a high voltage pulse to the lamp, an electric 

discharge is initiated between the two electrodes. The pulse continues until an electrical 

arc is established. The arc tube also contains a small amount of xenon that serves as a 

starting gas. The arc vaporizes the xenon and produces heat, which causes the sodium 

and mercury to vaporize as well. The lamp achieves full light output after approximately 

10 minutes. 
HPS Lamp Shapes and Sizes 

Module 2, Slide 10

 Some common HPS lamps. 

 

HPS lamps come in a variety of shapes and sizes. 

Nomenclature (the naming convention) of HPS lamps is standardized by ANSI 

(American National Standards Institute), but this system is generally not used by the 

manufacturers for ordering purposes. Each company has its own HPS trade name, and 

some reference to the trade name typically appears in the lamp designation. 

The names adopted by the three major manufacturers are: 

Company Trade Name 

GE Lighting Lumalux LU 

SYLVANIA Lucalox LU 

Philips Lighting Ceramalux C 
HPS Lamp Color Characteristics 

Module 2, Slide 11

Standard HPS lamps have poor color rendering properties. Typically, high pressure 

sodium lamps have a CRI (color rendering index) of 20-30 and correlated color 

temperatures (CCT) of 1900-2100 degrees Kelvin. The light from high pressure sodium 

lamps generally appears golden-yellow in color. 

Although color shift is not often discussed for high pressure sodium lamps, they can 

undergo a change in CCT throughout life. Some lamps may look green, deep yellow, or 

even pink near end of life due to individual differences in sodium loss and current rise. 

As the improved or "white" color high pressure sodium lamps age, they tend to shift to a 

warmer CCT, closer to that of standard high pressure sodium lamps 

.

Light sources differ in their ability to render the color of objects "naturally" or as we 

expect them to look. CRI expresses the color rendering capability of a lamp on a scale 

of 0 (no ability to render color) to 100 (the best ability to render colors natural). CRI is 

generally not a concern in roadway lighting except in populated areas, such as city 

streets and plazas, where there will be people and activities at night and the naturalness 

of colors will matter. 

CCT is a measure of the color appearance of the light emitted by a lamp, relating its 

color to the color of light from a reference source when heated to a particular 

temperature, measured in degrees kelvin (K). The CCT rating for a lamp is a general 

"warmth" or "coolness" measure of the appearance of its light output. However, contrary 

to the temperature scale, lamps with lower CCT rating, below 3000 K, are usually 

considered "warm" sources with a more yellowish appearance, while those with a CCT 

above 4000 K are usually considered "cool" with a more white appearance. 
HPS Lamp Life 

Module 2, Slide 12

 Average rated life for traditional light sources is the number of hours when 50% of a 

large group of lamps have failed. The actual life of any electric lamp is a median value 

of life expectancy. The actual life of any individual lamp, or group of lamps, may vary 

from the published average rated life. 

In general, high pressure sodium lamps have a long average rated life, which makes 

them suitable for applications that require low maintenance and possibly involve hardto-reach places, such as the tall poles used in outdoor lighting and high-ceiling 

applications in interior lighting. High pressure sodium lamp life ranges from 10,000 to 

40,000 hours. Lamp life for these lamps is rated based on an 11 hour-per-start burn 

cycle. It must be noted that operation for cycles shorter than 11 hours at a time reduces 

lamp life. 

The temperature of the coldest spot on the arc tube of a high pressure sodium lamp 

rises throughout its life, causing the vapor pressure to change and lamp voltage to rise. 

Once lamp voltage has risen to approximately 140% of its rated value, the lamp 

extinguishes, cools down, and then tries to restart. This cycling phenomenon signals the 

end of life and indicates that the lamp should be replaced. If not replaced promptly, 

damage to the ballast will occur. Manufacturers offer non-cycling high pressure sodium 

lamps to eliminate this problem. 
HPS Light Output and Distribution 

Module 2, Slide 13

 

An HPS lamp in a fixture. See how the reflector behind the lamp directs the light down 

and out of the fixture. 

Lumen depreciation (light output reduction) of an HPS lamp throughout its life. 

Neither temperature nor burning position appreciably affects the light output (lumens) of 

high pressure sodium lamps. However, the light output of these lamps decreases over 

time. The graph at right shows a lumen depreciation curve for high pressure sodium 

lamps. Lumen depreciation in these lamps is mainly due to the darkening of both the arc 

tube and the outer glass bulb, which reduce the amount of light that gets out of the 

lamp. Generally speaking, high pressure sodium lamps have very good lumen 

maintenance through their life (greater than 80%). 

Most high pressure sodium lamps emit light in all directions. In most applications, high 

pressure sodium lamps are used in luminaires that have a reflector behind or above the 

lamp. This allows the light from the lamp to be directed to where it is needed. The hard 

glass outer bulb wall of the lamps used in roadway lighting is typically clear. 
HPS Lamp Efficacy 

Module 2, Slide 14

 

The efficacy of HPS lamps (lumens/Watt) is quite high in comparison to other sources, 

but efficacy decreases as the CRI of the lamp improves and/or the CCT of the lamp 

increases. 

HPS lamp efficacies range from 64 to 140 lumens/Watt. The higher wattage high 

pressure sodium lamps also tend to have higher efficacies than their low wattage 

counterparts. 

As with other HID lighting systems, lighting professionals must consider the system 

input wattage (lamp + ballast), rather than the lamp's rated wattage when performing 

energy-use calculations. This is because the ballast will require a certain amount of 

power during operation. 

As shown in the example above, the ballast “adds” 45 additional Watts to the wattage of 

the 200 W HPS lamp when these are combined as an operating system. 
HPS Lamp Electrical Operation 

Module 2, Slide 15

 An HPS lamp and ballast. Also shown are a capacitor and an igniter. 

All HPS lamps require a ballast to start and operate the lamp. The ballast must be 

compatible with the particular lamp and the line voltage to which it is connected. 

Ballasts for high pressure sodium lamps can be either magnetic or electronic, but 

magnetic ballasts are by far the most common type used. 

HPS lamps need time to warm up when started to achieve full light output. Warm up 

time is generally up to 10 minutes. High pressure sodium lamps also need time for the 

arc tube to cool once extinguished before the lamp will restart. This "restrike" time 

generally ranges between 1 and 2 minutes. 

A few types of high pressure sodium lamps can be dimmed using an appropriately 

designed ballast and control system, but it is difficult and expensive to do so. It is not 

recommended to dim HPS lamps below 50% of their full light output. HPS lamps will 

become much more yellow when dimmed. 

Most HPS lamps contain a small amount of mercury. Therefore, gloves should be worn 

when handling broken lamp fragments. Most high pressure sodium lamps must be 

disposed of according to guidelines established by the U.S. EPA or other state or local 

authority. However, there are low/no mercury types that do not fall under these 

guidelines. Consult lamp manufacturers' catalogs for information on these lamps. 
Knowledge Check 

Module 2, Slide 16

Select the correct answer:

HPS lamps generally have a lumen depreciation of less than ____ over their lifetime. 

 a) 250 lumens 

 b) 20 percent 

 c) 80 percent 

 d) 100 footcandles 

The correct answer is on the next page. 
Knowledge Check Answer 

Module 2, Slide 17

The correct answer is "b" – 20 percent. 

HPS lighting systems maintain over 80 percent of their lumen output over the life of 

each lamp. (See Module 2, Slide 13) 
Mercury Vapor Lamps 

Module 2, Slide 18

 Left: Components of a mercury vapor lamp. Right: Photograph of a mercury vapor 

lamp. 

Developed in the early 20th century, mercury vapor (MV) lamps were the first HID 

lamps and are now the least efficacious. These lamps, which provide bluish-white light, 

were used in street lighting for years, because they were more efficient and had longer 

lives than incandescent lamps, which had been the primary light source used for 

roadway lighting prior to their introduction. Because of their low efficacies (37 to 56 

lumens per watt) and low CRIs (15 for clear versions and 50 for coated), mercury vapor 

lamps are used less often over the past few years. 

Federal legislation banned the sale of mercury vapor ballasts and luminaires after 2008, 

due to the low efficacy of MV lamps. New federal rules in the US ban the sale of screwbased mercury vapor lamps for general illumination by the end of 2017. These lamps 

are already banned in Europe, because they are not energy-efficient and a number of 

suitable replacements exist for these lamps, including metal halide, high pressure 

sodium, and LEDs. 
Low Pressure Sodium Lamps 

Module 2, Slide 19

 

 Components of an LPS lamp. 

 

Appearance of a roadway under LPS streetlighting. 

Although low pressure sodium (LPS) lamps are often categorized as HID sources, 

technically they do not fit into this category. With their characteristic deep-yellow color, 

low pressure sodium lamps have high efficacies. However, the CRI of low pressure 

sodium lamps is very low. Colors appear either as yellow or as shades of gray, making 

color identification extremely difficult. 

These lamps are rarely used for roadway lighting in the US, (mainly due to their poor 

color rendering capabilities) except around observatories, where their narrow emission 

wavelengths can be easily filtered out by astronomers. 
Metal Halide (MH) Lamps 

Module 2, Slide 20

The yellow "mouse-over" circles in the diagram above (from top to bottom) refer to the 

following lamp components: 

 Outer Bulb: Hard glass that protects the arc tube. 

 Electrode (1): Double coiled tungsten coated with emissive materials are located at 

each end of the arc tube. 

 Arc Tube: Quartz or ceramic structure suitable to withstand thermal stress and 

internal pressure during operation. 

 Electrode (2): Double coiled tungsten coated with emissive materials are located at 

each end of the arc tube. 

 Phosphor Coating: Provides slightly warmer CCTs and improves the CRIs of clear 

standard lamps. Lamps used for roadway lighting are typically not phosphor coated. 

 Base: Several different types used to connect the lamp to the electric circuit and to 

support the lamp in the lamp holder. The most common types are mogul and 

medium screw base. 

Metal halide (MH) lamps have superior color rendering abilities, compared to other HID 

lamps, and their light has a "white" color appearance. These lamps are used in exterior 

applications where color rendering is important and/or where a whiter light is preferred. 

Metal halide lamps produce light by an electric discharge through combined vapors of 

mercury and other compounds called halides. These gases are contained within the arc 

tube of the lamp under high pressure. The arc tube is surrounded by an outer hardglass bulb filled with a mixture of gases to help provide a stable thermal environment. 

The arc tube is generally made of either quartz or ceramic material. Ceramic arc tubes 

keep the lamp's operation more stable over time. 

Electrodes are usually embedded in each end of the arc tube of an MH lamp. When 

proper starting voltage is applied by the ballast through an igniter, which can be either 

located within or external to the lamp, an arc is established between the two electrodes. 

Heat from this arc causes the mercury and halides to vaporize, and a gradual color 

change occurs as the lamp warms up. Most metal halide lamps achieve full light output 

after 4-6 minutes; however, it can take even longer for lamps of higher wattage. 
MH Lamp Shapes and Sizes 

Module 2, Slide 21

 Various shapes and sizes of metal halide lamps. 

Metal halide lamps come in a variety of shapes and sizes. 

Nomenclature of metal halide lamps is standardized by ANSI, but this system is 

generally not used by the manufacturers for ordering purposes. Most standard 

screwbase metal halide lamp designations begin with the letter "M." 

Since the designations for metal halide lamps are too diverse for generalization, it is 

best to refer to the lamp manufacturers' catalogs for written descriptions that 

accompany ordering codes. 
MH Lamp Color Characteristics 

Module 2, Slide 22

Example of “color shift” (change in CCT) of MH lamps. As they age, these lamps can 

begin to change from emitting white light, to light that may appear green or pink. 

The CCT ranges of MH lamps are 2900 K to 5200 K. The CCT of standard metal halide 

lamps may shift over time due to variations in manufacturing, a change in the lamp's 

position or temperature, a variation of the supply voltage, or when the lamp begins to 

age. This should not be an issue with roadway lighting, where color appearance of light 

is not an important factor. 

"Improved color" MH lamps with ceramic arc tubes (typically referred to as ceramic 

metal halide lamps) have improved color rendering capabilities and are designed to 

reduce color variation over time. 

Metal halide lamps exhibit color rendering properties that can range from fair to very 

good, depending on the lamp selected. Improved color rendering ceramic MH lamps 

have CRIs of 80 or above. 

Standard MH Lamps - CRI 60-75

Ceramic MH Lamps - CRI 80-95
MH Lamp Life and Light Output 

Module 2, Slide 23

 

 Lumen depreciation curves for various types of MH lamp/ballast systems. 

Life 

In general, MH lamps have a long average rated life, which makes them suitable for 

applications that require low maintenance and possibly involve hard-to-reach places, 

such as in roadway lighting. MH lamp life ranges from 5,000 to 20,000 hours. Lamp life 

for these lamps is rated based on an 11 hour-per-start burn cycle. It must be noted that 

operation for cycles shorter than 11 hours at a time will result in reduced lamp life. 

Light Output 

Metal halide lamps can be affected in their light output (lumens) by a number of different 

factors. First and foremost is the fact that light output decreases over time due to 

material deposits and transformation of the chemical elements inside the arc tube. 

Lamp manufacturers not only publish "initial" lumens (100% of light output) but also 

"mean" lumens (light output at 40% of the lamp's rated life) for metal halide lamps. 

A lighting professional must take lumen depreciation into account when performing 

illuminance calculations to ensure that the lamps will deliver the desired light levels well 

after the lighting system has been installed. Newer electronic ballasts with pulse start 

technology have improved lumen maintenance so that some metal halide lamps lose 

less than 20% of their light output over their rated life. 
MH Lamp Light Distribution 

Module 2, Slide 24

 Various orientations of MH lamps. 

Light Output 

Generally speaking, ambient temperature does not affect the light output of metal halide 

lamps. In some cases, though, light output of metal halide sources is affected by lamp 

orientation or burning position. Manufacturers label lamps so users can select the ones 

that will function best in their application. For example, a lamp may be labeled as shown 

at left. 

Light Distribution 

Metal halide lamps with clear glass envelopes are generally considered to be "point 

sources" because their light is emitted from a relatively small area, the arc tube. This 

allows the light from the lamp to be efficiently directed using a reflector as part of an 

appropriately designed luminaire. Metal halide lamps can also provide a more diffuse 

light by means of a phosphor coating that is applied to the inside of the glass bulb wall. 

These lamps are marked "C" for coated and are generally not used in roadway lighting 

luminaires. 

Lighting professionals might want to consider LED (light emitting diode) lamps or 

luminaires instead of MH. LEDs are more efficient, have a longer rated life, turn on 

instantly with no warm up time required, and are available in a similar range of CCTs. 
MH Lamp Efficacy 

Module 2, Slide 25

In general, MH lamps are very efficacious sources. Efficacies of standard metal halide 

lamps range from approximately 56 to 110 lm/W, with lamps of higher wattages 

achieving higher efficacy. Efficacies of improved-color metal halide lamps are not as 

high as the standard lamps. Improved-color metal halide lamps usually range between 

70 to 90 lm/W. Lighting professionals must consider the system input wattage (lamp + 

ballast) rather than the lamp's rated wattage alone when performing energy-use 

calculations. Similar to a fluorescent lighting system, the ballast in a metal halide system 

will require a certain amount of power during operation. 
MH Lamp Electrical Operation 

Module 2, Slide 26

 Wiring diagram of a MH/ballast system. 

All higher wattage MH lamps require a ballast to start and operate the lamp. The ballast 

must be compatible with the particular lamp chosen and the line voltage to which it is 

connected. Ballasts for metal halide lamps can be either magnetic or electronic. Newer 

electronic ballast technology is typically more efficient than magnetic technology. 

MH lamps need time to warm up when started to achieve full high output. They also 

need time when extinguished for the arc tube to cool before the lamp will restart. This is 

known as the lamp's "restrike" time, and it varies among lamp types and wattages. 

Some metal halide lamps can be dimmed using an appropriately designed ballast and 

control system, but it is difficult and expensive to do so. In general, metal halide lamps 

respond to changes in dimmer settings much more slowly than incandescent or 

fluorescent sources. Lamps should be started at full power, with dimming delayed until 

the lamp is fully warmed up. Properly designed dimming systems ensure that this 

occurs. Metal halide lamps are also susceptible to color shifts (changes in CCT) when 

dimmed. It is recommended that metal halide lamps not be dimmed below 50% of full 

light output. 
Pulse-Start MH Systems 

Module 2, Slide 27

 Detail of a pulse-start metal halide lamp arc tube. 

An MH lighting system, commonly known as a "pulse start," has become the standard 

metal halide technology. Pulse start lamps operate on a ballast with a pulse igniter 

located external to the lamp. Pulse start metal halide lamps have improved efficacies 

as compared with standard metal halide lamps. Pulse start lamps have higher initial and 

mean lumens, longer life (up to 40,000 hours), improved color stability, and faster 

restrike times (as short as 4 minutes). 

When planning to replace an existing metal halide system with pulse start technology, 

lighting professionals should keep in mind that the ballast and lamp socket will need to 

be replaced in addition to the lamp itself. These replacement components will usually fit 

into the existing luminaire housing. New metal halide systems available on the market 

will be designed to use pulse start technology. Older, “probe start” technology has been 

phased out through government regulations. 
MH Lamp Safety 

Module 2, Slide 28

 MH lamp in an enclosed luminaire. 

Because of their "warm up" and "restrike" times, do not use metal halide lamps in 

situations where instantaneous start is required. Most metal halide lamps should be 

operated within enclosed luminaires or have other protective measures to guard against 

possible end-of-life rupture and to filter ultraviolet light. Be sure to check the lamp 

manufacturer's catalog to determine if a particular lamp is rated for use in open 

luminaires. MH lamps contain a small amount of mercury. Therefore, gloves should be 

worn when handling broken lamp fragments. Always dispose of metal halide lamps 

according to guidelines established by the U.S. EPA or other appropriate state or local 

authority. 

In any application where lamps are operated continuously (24 hours per day, seven 

days per week), the lamps should be turned off once per week for a period of at least 15 

minutes to reduce stress on the glass caused by extreme pressure within the lamp. This 

may reduce the possibility of non-passive failure (end-of-life rupture). 
Knowledge Check 

Module 2, Slide 29

Select the correct answer:

An important feature of a pulse start metal halide lighting system is _____. 

 a) Higher maintained lumens 

 b) Longer lamp life 

 c) Faster restrike times 

 d) All of the above 

The correct answer is on the next page. 
Knowledge Check Answer 

Module 2, Slide 30

The correct answer is "d" – All of the above. 

All of the attributes listed: 

 Higher maintained lumens 

 Longer lamp life 

 Faster restrike times 

Are features of pulse start metal halide lighting systems. (See Module 2, Slide 27)
Plasma Lighting Systems 

Module 2, Slide 31

 High mast lighting, like that shown in the picture above, is possibly a good fit for plasma 

lighting systems. 

Plasma lighting systems, also known as light-emitting plasma (LEP), high-efficiency 

plasma (HEP), or advanced plasma lighting (APL) are emerging in the marketplace 

primarily for high ceiling interior applications and outdoor lighting applications. These 

lamps are essentially electrodeless metal halide lamps. 

Manufacturers claim that plasma lighting systems are better suited for roadway, area 

and high mast lighting applications than conventional HID and LED systems because of 

their long life, high luminaire efficiency, and low overall system price. They also claim to 

have accurate color rendering (95 CRI) and controllability for dimming and motion 

sensing. 

For roadway lighting applications, an evaluation conducted by the Lighting Research 

Center (LRC) in 2013 found that plasma lighting systems were no more effective or 

energy efficient than other HID lighting systems. This evaluation also found that LED 

systems were approximately 30% more efficient than available plasma lighting systems. 

(See the resource slide at the end of this course module for a link to this report.) 
Plasma Lighting System Operation 

Module 2, Slide 32

 A plasma lighting system. 

Plasma lighting systems are electrodeless metal halide lamps that produce light directly 

from an arc discharge operated under high pressure. The arc discharge is powered by a 

high-frequency electromagnetic field generated externally to the lamp. This is different 

from conventional HID lamps which have electrodes within the arc tube that convey 

current to sustain the arc discharge. 

Plasma lighting systems are also known as electrodeless HID systems, however, they 

are typically referred to by the generic term “plasma lighting system” in the lighting 

industry. 

Plasma lighting systems typically have multiple components including: 

 a lamp or emitter which contains the light-emitting gas that operates under high 

pressure 

 an applicator or resonator for “coupling” the power to the lamp

 a high-frequency ballast/driver, such as a radio frequency (RF) generator or 

magnetron (microwave) generator. 
Plasma Lamps Shapes and Color 

Module 2, Slide 33

 

 Examples of plasma lamps. 

Shapes 

There is no standard naming system for plasma lamps, and the lamps and other system 

components such as the resonator and power supply or ballast must be purchased from 

the same manufacturer as the lamp. At the left are examples of plasma lamps with their 

resonators or applicators. Some manufacturers have limits on the orientation of their 

plasma lamps, so it will be important to check with the manufacturer before determining 

the system to purchase for your application. 

Color Characteristics 

The CRI of plasma lighting systems range from 70 to 95, making them acceptable for all 

exterior applications. Each manufacturer offers different CCTs for their product, ranging 

from 3200 to 7650 K. Similar to conventional metal halide lamps, shifts or changes in 

the CCT of the light from plasma lamps may occur as lamps age. The CCT is also 

affected by lamp orientation. The light from plasma lighting systems may also appear to 

have a greenish-white tint. 
Plasma Lamp Life and Efficacy 

Module 2, Slide 34

 Efficacy and light output of plasma lighting systems. 

Life 

Manufacturers claim that plasma lighting systems have longer rated life than HID lamps 

because they are electrodeless. The rated life of plasma lighting systems typically 

ranges from 30,000 to 50,000 hours depending on manufacturer and product. Topanga, 

whose plasma lighting system allows for the replacement of the arc tube separately 

from the RF driver, specifies that the life of the emitter is 50,000 hours while the life of 

the RF driver is 100,000 hours. 

Light Output and Efficacy 

The rated light output for plasma lighting systems ranges from 11,000 lumens (lm) (with 

an input power of 130 W) to 50,000 lm (with an input power of 455 W), with system 

efficacies ranging from 50 lm/W to 110 lm/W, as shown in the graph above. The system 

efficacies include the power demand of the commercial dc power supply. The 

manufacturers' specified efficacies are shown in the graph as a function of rated light 

output. Typically, products with a higher light output have a higher efficacy. 
Plasma Lamp Electrical Operation 

Module 2, Slide 35

 Left: CCT increases as plasma lamp is dimmed. Right: Efficacy decreases as plasma 

lamp is dimmed. 

Electrical Operation 

Plasma lighting systems do not achieve their full light output immediately after starting. 

Rather, they require a few minutes to warm up. After the plasma lighting system has 

been on for a period of time and then extinguished, the lamp cannot immediately turn 

back on. The lamp must have a chance to cool down before the system will restart 

(restrike). Warm up and restrike times for plasma lighting systems can range from 2 to 6 

minutes. Plasma lighting systems operate at high frequencies and can be a source of 

both radiated and conducted electromagnetic interference (EMI). If the luminaire 

containing the plasma lighting system is not shielded, the luminaire can cause 

interference with other electronic equipment. 

Dimming 

Plasma lighting systems can be dimmed, but dimming these systems results in color 

shifts (changes in CCT) and decreases in luminous efficacy. Most plasma lighting 

system manufacturers specify that their products are dimmable down to 20% of 

maximum light output. The graphs above show the changes in efficacy and CCT as two 

plasma lamps tested were dimmed. 

Safety 

Plasma lamps contain small amounts of mercury. Gloves should be worn when handling 

any broken lamp fragments. These lamps should be disposed of or recycled in 

accordance with applicable U.S. E.P.A. guidelines. 
Knowledge Check 

Module 2, Slide 36

Select the correct answer:

When dimming a plasma lighting system, the efficacy (lumens per watt) 

generally _____. 

 a) Increases 

 b) Remains the same 

 c) Decreases 

 d) Cannot be determined 

The correct answer is on the next page. 
Knowledge Check Answer 

Module 2, Slide 37

The correct answer is "c" – Decreases. 

When a plasma lighting system is dimmed the system efficacy (lumens per watt) 

decreases. (See Module 2, Slide 35)
Electrodeless Induction Lamps 

Module 2, Slide 38

 Electrodeless lamps used for street lighting. 

Inductive discharge lamps, commonly known as induction lamps, are available from a 

number of global lighting manufacturers. These lamps are essentially electrodeless 

fluorescent lamps. The main differences between these and the more common 

fluorescent lamp technologies is their use of an electromagnetic field, rather than an 

electric arc passing between the electrodes, to excite the mercury in the gas within the 

bulb, which in turn excites the phosphors on the bulb wall producing light. Because it is 

usually the damage caused to the electrodes that is responsible for most fluorescent 

lamp failures, eliminating the need for electrodes in a fluorescent lamp should extend its 

life significantly. 

Induction lamps are relatively large devices and come in high lumen packages, with 

significant light output per lamp, and are therefore typically used in parking lot, tunnel, 

and roadway applications. 
Induction Lamp Operation 

Module 2, Slide 39

 The yellow "mouse-over" circles in the diagram above (from top to bottom) refer to the 

following lamp components: 

 Outer bulb 

 Gas and mercury fill 

 Phosphor coating 

 Induction coil 

 Radio frequency power supply 

In an induction (electrodeless) lamp, light is generated by means of induction (the 

transmission of energy via an electromagnetic field) combined with a gas discharge 

within a bulb. The induction lamp system is powered by a radio frequency power supply 

which sends an electric current to an induction coil (a wire wrapped around a plastic or 

in some cases a metal core interior to the lamp). This current generates an 

electromagnetic field when it passes through the induction coil. This electromagnetic 

field excites the mercury in the gas within the lamp causing it to emit ultraviolet energy. 

This ultraviolet energy in turn strikes and excites the phosphor coating on the inside of 

the glass bulb, producing light. 

When turned on, induction lamps start instantly, and unlike HID lamps, there is no delay 

in restrike time. The lamps can be mounted in any orientation. The figure above shows 

the construction of one common type of induction lamp system. 
Induction Lamp Shapes and Color 

Module 2, Slide 40

 Left: Philips Induction Lamp. Right: SYLVANIA Icetron Lamp. 

Lamp Shapes and Sizes 

There are two common configurations for the induction lamps sold by major lighting 

manufacturers. The nomenclature, or lamp-naming system for these lamps, has been 

established separately by each manufacturer and follows no standards. 

Two common electrodeless fluorescent lamps are, the "Induction Lamp" (also known as 

QL lamp) manufactured by Philips Lighting and the "Icetron" manufactured under the 

trade name SYLVANIA. These generally come in higher wattages, best suited for 

outdoor use where a lamp with a high lumen output is desired. 

Color 

Because induction lamps utilize the same kind of improved phosphor technology as the 

new generation of fluorescent lamps, their color rendering properties are very good. 

They generally achieve color rendering indexes of 80 or higher. Each manufacturer 

offers different correlated color temperatures for their product, ranging from 2700 to 

4100 K. 
Induction Lamp Life 

Module 2, Slide 41

 

 Induction lighting installed in Union Square Park in New York City. 

Life 

The main benefit of using induction technology to generate light is long system life. The 

system's life in this case is governed mainly by the life of the electronic components in 

the high-frequency generator that powers the lamp, which may have a shorter life than 

the lamps themselves. Philips Lighting and SYLVANIA currently rate the life of their 

induction lamps at or near 100,000 hours. This life expectancy is greater than that of 

many other traditional light sources, making it a good choice for applications that require 

low maintenance or involve hard-to-reach places. 

However, with long life linear fluorescent lamps now on the market with rated lives of 

85,000 hours, and some LED systems that can have rated lives nearly as long, the life 

of induction lamp technology is no longer as exceptional as it once was. There is also 

no industry standard for testing induction systems, so it is not clear how system life is 

derived. 
Induction Lamp Output and Efficacy 

Module 2, Slide 42

 Left: Lumen depreciation curves of two induction lamps. Right: Illustration of induction 

lamp light distribution. 

Light Output and Distribution 

As with all fluorescent lamps, the light output of induction lamps decreases over time 

due to the degradation of the light-emitting phosphors that coat the glass bulb. This 

process is known as lumen depreciation. The graph at right depicts the lumen 

depreciation of two different induction lamps. It is also important to note that while the 

lamps turn on instantly, it takes several minutes for them to reach full light output. 

Because these lamps produce light by exciting a phosphor coating on the bulb's wall, 

their distribution is generally diffuse, making it somewhat difficult to direct with optics 

such as reflectors. 

Efficacy 

Induction lamps exhibit good efficacy, ranging from 70 to 89 lumens per Watt. This 

efficacy range is comparable to many fluorescent and HID lamps. For induction lamps a 

lighting professional should use total system watts (lamp plus power supply) when 

performing energy calculations because a certain amount of power will be used by the 

power supply itself. 
Induction Lamp Electrical Operation 

Module 2, Slide 43

 

 Compared to the HPS lighting in the background, induction lighting is a much whiter 

light source. 

Electrical Operation 

Induction lamp systems are available in 120 and 240 volts. All of these lamps require a 

radio frequency power supply to start and operate the lamp. In induction lamp systems 

this power supply is external to the lamp itself. Induction lamps are electronic devices, 

and like all electronic devices they generate electromagnetic waves. To avoid 

electromagnetic interference (EMI), which may be caused by these lamps, be sure to 

use them in accordance with manufacturer specifications. 

Safety 

Induction lamps generate electric and magnetic fields during operation. Special care 

should be taken when using them in close contact with devices that are sensitive to 

these fields. These lamps also contain small amounts of mercury. Gloves should be 

worn when handling any broken lamp fragments. These lamps should be disposed of or 

recycled in accordance with applicable U.S. EPA guidelines and/or state and local 

ordinances. 
Knowledge Check 

Module 2, Slide 44

Select the correct answer:

In an induction lamp, light is generated by means of ______ combined with a gas 

discharge. 

 a) Heating a tungsten filament 

 b) The transmission of energy via an electromagnetic field 

 c) An electric arc passing between two electrodes 

 d) Heating a carbon electrode 

The correct answer is on the next page. 
Knowledge Check Answer 

Module 2, Slide 45

The correct answer is "b" – The transmission of energy via an electromagnetic field. 

The main differences between electrodeless induction lamps and the more common 

fluorescent lamp technologies is their use of an electromagnetic field, rather than an 

electric arc passing between the electrodes, to excite the mercury in the gas within the 

bulb, which in turn excites the phosphors on the bulb wall producing light. (See Module 

2, Slide 39)
LEDs (Light Emitting Diodes) 

Module 2, Slide 46

 Left: The spectral power distribution (SPD) of a phosphor-coated LED. Right: Examples 

of phosphor-coated LEDs. 

Light emitting diodes, commonly referred to as LEDs, are small electronic light sources. 

They are available in a variety of colors including red, amber, green, and blue. Unlike 

many other light sources that produce colored light by using a filter placed over the 

lamp, LEDs produce "true" colored light in narrow wavelengths within the visible 

spectrum. Prior to the 1990s, when the blue LED was developed, LEDs were commonly 

seen as colored indicator lights on electronic equipment such as stereos. Colored LEDs 

are currently used in a wide range of lighting applications including signage, traffic 

signals, and vehicle signal lighting. 

The most common means of creating white light using LEDs is to cover a blue or short 

wavelength LED with a phosphor. The short wavelength radiation from the LED excites 

the phosphor, creating white light with the combination of the blue light emitted directly 

by the LED and the light emitted by the phosphor. This type of LED is typically referred 

to as a phosphor converted or “PC” LED. 
LED Operation 

Module 2, Slide 47

In the illustration above, the following terms are shown: 

The band gap refers to the energy difference (in electron volts) between the top of the 

valence band and the bottom of the conduction band in semiconductors. The 

conduction band is normally empty and may be defined as the lowest unfilled energy 

band. In the conduction band, electrons can move freely and are generally called 

conduction electrons. The valence band is the highest range of electron energies in 

which electrons are normally present. P-type semiconductors have a larger hole 

concentration than electron concentration. The term p-type refers to the positive charge 

of the hole. In p-type semiconductors, holes are the majority carriers and electrons are 

the minority carriers. An n-type semiconductor is created by adding impurities, called 

dopants. The purpose of doing this is to make more charge carriers, or electrons 

available in the material for conduction. In n-type semiconductors the number of 

electrons is more than the holes, so electrons are measured as majority charge carriers 

and holes are referred to as minority charge carriers. Electrons are the lightest stable 

subatomic particle known. An electron carries a negative charge, which is considered 

the basic unit of electric charge. 

LEDs are semiconductors, which convert electrical energy directly into light. The light is 

generated inside a small semiconductor chip, which is a solid crystal material. The 

different layers of crystal in the semiconductor chip determine the wavelength, or color, 

of light emitted. Aluminum indium gallium phosphide (AlInGaP) and indium gallium 

nitride (InGaN) are two of the most common compounds. 

As seen in the illustration, LEDs are made up of “P-type” material with slight electron 

“deficiency” or holes for molecular bonding; and “N-type” material with excess electrons 

leftover from the crystal bonding process. Photons (light) are generated when the 

positive and negative charges recombine and release energy. 

Not all recombinations of electrons within the LED result in light. Charges that are 

trapped in defects within the LED result in heat. It is also important to note that about 

70% of the light generated by an LED is trapped within the device. This trapped light 

also results in heat. 
LED Lamp Shapes and Sizes 

Module 2, Slide 48

 

 An LED mogul screwbase lamp that could be used to replace an MH or HPS lamp in an 

existing roadway lighting luminaire. 

LEDs are not typically purchased as single devices or packages. They are purchased 

as lighting systems (lamps or luminaires) that include the LEDs and the electronic and 

optical components needed for them to operate and distribute their light properly. 

LED Screwbase Lamps 

LED mogul screwbase lamps are available to replace HPS, MH, and mercury vapor 

lamps. However, these lamp may not operate well in existing luminaires designed to 

house these other light sources. For example, because roadway luminaires are typically 

tightly enclosed, heat will build up around the LED lamps. This heat will negatively affect 

the light output, color appearance, and life of LED lamps. Some of these replacement 

lamps will operate on the existing ballast within the luminaire, while others will require 

that the ballast be bypassed or removed and the lamp sockets wired directly to line 

voltage. 
Selecting LED Replacement Lamps 

Module 2, Slide 49

 

Another LED mogul screwbase LED replacement lamp. 

When selecting LED replacement lamps it is important to consider how the LED lamp 

will function within the existing luminaire. For most roadway lighting luminaires, the 

optical distribution of the luminaire will be altered by the LED replacement lamp. As 

such, the luminaire might not still provide the distribution or light levels needed on the 

roadway. 

LED lamps marketed as “replacements” for typical wattages of existing lamps will 

sometimes provide significantly less light than the lamps they are marketed to replace. 

Therefore, it is important to match the lumen output of LED replacement lamps as 

closely as possible to existing lamps. 

If the ballast of the existing luminaire is bypassed and line voltage provided directly to 

the lamp sockets the sockets may not be designed to handle line voltage safely. Also, 

any attempt to replace the LED lamp with the original technology, such as an MH lamp, 

may result in rupture or explosion of the lamp when operated directly on line voltage. 

Due to their heat sinks, LED lamps may also be too heavy to be properly supported by 

the socket within the existing luminaire. 
LED Life 

Module 2, Slide 50

 

The life of an LED lamp or luminaire is when the LED’s lumen depreciation is expected 

to reach 70% of its initial light output. 

One of the advantages of LEDs is their long life. Life ratings for LED lamps and 

luminaires for roadway lighting range from a low of 30,000 hours to as much as 85,000 

hours or more. Unlike other light sources, LEDs do not generally cease to produce light. 

Instead, their light output degrades gradually over time. Therefore, manufacturers rate 

the end of life of LEDs at a certain percentage of their initial light output value, typically 

70%. This “lumen depreciation” metric is typically referred to as “L70.” 

Life for LEDs is determined by operating individual LEDs under a standard set of 

conditions (continual operation; at least 3 different temperatures) for between 6,000 and 

10,000 hours. The data obtained from this test period is then put into an “exponential 

decay” model which is used to predict the point at which the LED will reach 70% of its 

light output. This information is then used by luminaire and replacement lamp 

manufacturers to determine the rated life of their products. 

The problem with using this lumen depreciation metric as a life predictor for an LED 

product is that it only pertains to the LEDs themselves, and does not take into account 

the many other components within an LED lamp or luminaire. 
LED Life and Color 

Module 2, Slide 51

 

 The LED roadway luminaires shown above have a CCT rating of 6000 K, providing a 

bright white light along this roadway. 

Life 

The lighting industry is currently working on a life test method that will better quantify the 

life of an entire LED system including electrical and other components. However, until 

this new method is agreed upon, lighting practitioners should look carefully at long life 

claims. It might be reasonable to expect an LED product to last up to 50,000 hours. 

However, a life of 100,000 hours or more may be an unreasonable prediction. 

The main factor that will shorten the life of an LED product is heat. Manufacturers will 

typically set limits for the temperatures under which their products will operate 

effectively and provide the expected life and light output. Every 10 degrees Celsius (C) 

an LED product is operated above its rated temperature will shorten its life by 

approximately 10%. Therefore, it is very important to be aware of these temperature 

limits and carefully adhere to them. 

Color 

LED lamps and luminaires can be found with a range of CRI’s that will easily meet the 

requirements for roadway lighting. LEDs can also be found in a range of CCTs from 

2700 K to 6500 K. 
LED Light Output and Distribution 

Module 2, Slide 52

 

 A close up image of an LED roadway luminaire. 

The light output and distribution of LEDs is dictated by the lamp or luminaire in which 

they are operated. Light output is increased by adding more LEDs to a lamp or 

luminaire or using LEDs of higher light output. Distribution can be altered through the 

use of reflectors, lenses, or other optical components. 

When considering replacing existing roadway lighting with LEDs, it is often best to 

select an LED luminaire rather than a replacement lamp. This will provide the best light 

distribution, efficacy, and life for the LEDs. 

Currently available LED roadway luminaires will meet North American roadway lighting 

design criteria (light levels, uniformity ratios, glare) at similar or better pole spacing than 

common HPS solutions. A few LED products can be spaced up to 280 ft apart 

compared with an average of 220 ft for HPS systems.

LED Electrical Operation and Dimming 

Most LEDs are low voltage DC (direct current) devices and require a driver to start and 

operate the LEDs. A driver is similar to a ballast in an HID system. Many LED roadway 

luminaires are available with drivers that allow them to be dimmed using a compatible 

control such as an occupancy sensor, time clock, or other controller. 
LED Efficacy 

Module 2, Slide 53

 

 LED efficacy predictions through 2025. 

For a long time the efficacies of white light LEDs have been a constantly moving target, 

with efficacies increasing year over year. The U.S. Department of Energy (US DOE) 

publishes a “roadmap” which tracks the efficacies of LEDs and makes predictions for 

efficacy improvements in the future. The graph at left shows the efficacy predictions for 

phosphor converted LEDs. 

Although individual LEDs may be available approaching 200 lumens per watt, LED 

lamps and luminaires cannot achieve these efficacies. This is because of electrical, 

thermal, and optical losses of the LED lamp or luminaire. This means that an LED 

product will typically achieve only about 60% of the efficacy of the LEDs it contains. So 

expect to see roadway luminaires with efficacies between 85 and 120 lumens/Watt. 

Typically an LED roadway lighting installation will use 15% to 40% less energy than a 

comparable HPS system, making LEDs the most efficient system you can buy. 
Knowledge Check 

Module 2, Slide 54

Select the correct answer:

The life of an LED product is based on the point at which ________. 

 a) The electrical components within the product are expected to fail 

 b) 50% of the LEDs operated for a test period have failed 

 c) The LEDs within the product are expected to lose 30% of their light output 

 d) The LEDs within the product will lose 70% of their light output 

The correct answer is on the next page. 
Knowledge Check Answer 

Module 2, Slide 55

The correct answer is "c" – .The LEDs within the product are expected to lose 30% of 

their light output. 

The life of an LED product is based on the point at which the LED within the product are 

predicted to lose 30% of their light output. 

Unlike traditional light sources whose life is based on testing until the product is no 

longer operational, LED life is based on light output (lumen) depreciation (See Module 

2, Slide 50) 
Summary of Key Light Source Operating Factors 

Module 2, Slide 56

The table above summarizes some key factors for each type of light source covered in 

the previous section of this course module including: average rated life, efficacy in 

lumens per watt, correlated color temperature (CCT), and color rendering index (CRI). 
Summary of Key Light Source Considerations 

Module 2, Slide 57

***

The table below reviews some of the important considerations when using each light 

source type for roadway lighting. 
Roadway Luminaire Classifications 

Module 2, Slide 58

The next portion of this module will go over roadway luminaire classifications. 
Luminaire (Light Fixture) 

Module 2, Slide 59

 

IES (Illuminating Engineering Society) Definition: a complete lighting unit consisting 

of a light source or light sources and a ballast or driver (when applicable) together with 

the parts designed to distribute the light, to position and protect the light source(s), and 

to connect the light source(s) to the power supply. 

Primary Luminaire Components 

Roadway luminaires come in many shapes, sizes, and designs. The type of luminaire 

you select typically depends upon its aesthetic appropriateness for the site as well as its 

function and ability to deliver light where needed. In all cases, the luminaire will have a 

housing, usually made of steel. For HID luminaires. the housing will typically include a 

lamp socket, a reflector, and a ballast or driver compartment. For LED luminaires, the 

LEDs will either be built directly into the luminaire, be configured as a replaceable 

component. 

The luminaire would typically be enclosed by some type of lens that has a gasket to 

keep out dirt, insects, and prevent water infiltration into the luminaire housing. 
Luminaire Classification System "BUG" 

Module 2, Slide 60

 An illustration of the IES luminaire classification system or BUG rating. 

The “BUG” rating of a roadway luminaire does not describe its ability to attract insects. It 

describes the vertical distribution of the luminaire in terms of: 

Backlight (B) – the amount of light the luminaire emits behind the pole on which it is 

mounted 

Uplight (U) – the amount of light the luminaire emits directly into the sky 

Glare (G) – the amount of light the luminaire emits at high angles, which may cause 

glare when viewing the luminaire. 

The remaining light classified by this system is the forward light emitted by the 

luminaire, which is considered to be the useful portion. However, in some cases, the 

other portions of the light, such as backlight, may also be useful, if there were an area, 

such as a walkway, behind the pole that you wished to light. 

This luminaire classification system is illustrated above. 
Luminaire BUG Rating 

Module 2, Slide 61

 

 Illustration of BUG rating light distribution zones: 

 Uplight (above 90 degrees) into the sky will contribute to sky glow. This is 

wasted light. 

 High angle light (between 80 and 90 degrees) is likely to cause glare for 

oncoming drivers. 

 Useful forward light (between 0 and 80 degrees at the front) onto the 

roadway. 

 Back light (between 0 and 80 degrees at the back). Only useful if there is 

something to light off the side of the roadway, such as a sidewalk or path. 

The BUG rating was developed primarily to assist lighting practitioners to assess 

luminaires as contributors to light pollution. Light pollution is considered unwanted light 

up into the sky that contributes to skyglow, and hinders our view of the night sky. The 

luminaire uplight portion would be considered to contribute to skyglow. Some 

municipalities place limits on the amount of uplight a luminaire can produce. Another 

factor that could be considered light pollution is light leaving a site, such as from 

roadway or street; this is typically referred to as light trespass. The backlight portion of a 

luminaire placed at the edge of a roadway, for example, could contribute to light 

trespass. High angle light from the luminaire contributes to glare, and therefore should 

be limited, especially in roadway luminaires. 

There are typically 10 “zones” of light that are shown in this luminaire classification 

system, four forward light zones, four backlight zones, and two uplight zones. The 

illustration at the right shows a typical BUG report for a roadway luminaire. 
Luminaire Light Distribution 

Module 2, Slide 62

 

 Luminaire distribution types. 

Luminaire type 

There are several methods used by lighting practitioners and manufacturers to describe 

the distribution of pole mounted luminaires. These categories were developed and 

standardized in North America by the Illuminating Engineering Society (IES). The first 

method describes the lateral light distribution that the luminaire provides across the 

roadway. These distribution categories are used for most roadway luminaires. The chart 

at left shows the five types of lateral light distributions produced by pole mounted 

exterior luminaires. These are in plan view, as if you were looking down from above the 

luminaire at the distribution of light on the ground. 

Type I and II are typically used for roadway lighting. For large parking lots, type III and 

IV are common. 

The other commonly used light distribution term describes the luminaire’s vertical light 

distribution along the roadway. The possible choices for vertical distribution are short, 

medium, and long. The “long” distribution provides light over the longest distance along 

the roadway. 
Luminaire Shapes and Sizes 

Module 2, Slide 63

 Left: Cobra head luminaire. Center: Post top luminaire. Right: High mast luminaire. 

A very common roadway luminaire is typically referred to as a “cobra head”(1) because 

of its shape. These are usually lamped with HPS or MH lamps, but could also include 

electrodeless fluorescent or plasma lamps. These luminaires can be distribution types I 

through IV. 

A luminaire that is mounted on top of a pole is typically referred to as a “post top” (2). 

This type of luminaire is usually mounted at a lower height to provide a more 

“pedestrian scale” to the lighting. These can be lamped with a wide variety of source 

types, including HPS, MH, electrodeless fluorescent, or LEDs. A post top luminaire can 

be designed to distribute light all around the post (type V) or in a particular direction with 

distribution types I through III. 

Another type of roadway luminaire is typically referred to as “high mast” (3) lighting. As 

its name implies, this type of lighting system usually includes a number of luminaires 

mounted on a very tall (often 100 ft. or more) pole. These are used to light large areas 

such as highway interchanges. These typically use HPS, MH, or plasma lamps, but LED 

versions are also available. High mast luminaires will typically have a motorized system 

to raise and lower the luminaires for cleaning and relamping. Although this type of 

lighting can be very effective at lighting large areas uniformly at night, it should generally 

not be used near residential or other areas where light pollution or light trespass might 

be an issue. 
Luminaire Design Considerations 

Module 2, Slide 64

 

 Luminaires in the median of this roadway provide uniform lighting on each side of the 

street. 

There are several things that need to be considered when selecting roadway luminaires. 

Light Distribution - The most important design consideration is if the luminaire 

provides light where needed. It is very important to select a luminaire with the light 

distribution that best suits the needs of the site. 

Pole Height and Spacing - It is also important to optimize the pole height and spacing 

of an installation to provide the most uniform lighting possible. When selecting new 

luminaires for existing poles, this can be a challenge since pole location and height can 

often not be changed. Pole height and spacing will affect both light levels (illuminance) 

as well as illuminance uniformity, which is a key factor in good roadway lighting design. 

Glare Control – Glare is an important issue to control at night when peoples’ eyes are 

adapted to low light levels. This can be done by selecting luminaires with low light 

output in the “glare zone” between 80 and 90 degrees (see BUG rating). Luminaires 

should also be well shielded with high quality optical materials or by recessing the light 

source up into the housing of the luminaire. 
Luminiare Design Considerations (continued) 

Module 2, Slide 65

 

 An example of a high mast lighting installation. This is probably not the correct solution 

for a residential area, but may work well at a freeway interchange. 

Aesthetics and Appearance – Roadway luminaires will be visible both at night and 

during the day. Therefore it is important to select luminaires that fit the style and 

character of a site. Roadway luminaires come in many designs from historic to 

contemporary. 

Light Pollution – It is important to select luminaires that will control the light well so as 

not to send light directly up into the sky, or onto adjacent properties. 

Controls – At a minimum, roadway luminaires should always be controlled by either a 

photosensor or an astronomical timeclock. These will ensure that the luminaires are 

only operated during nighttime hours. In areas that are not used heavily late at night, 

you might also consider using a timeclock or other method to dim the lighting during late 

night hours. LED luminaires are easily dimmed and will instantly come up to full light 

output when needed. 

Nighttime Vision – At night, the sensitivity of the human eye shifts towards shorter 

wavelengths of light. This means that lighting that is generally more “blueish white” such 

as the light produced by MH, plasma lamps, or LEDs, will better meet the visual needs 

of people. This type of light will also generally be perceived as brighter, making people 

feel safer. 
Knowledge Check 

Module 2, Slide 66

Select the correct answer:

A roadway luminaire with a "Type I" distribution would be effective at lighting a narrow 

(two lane) roadway. 

 a) True 

 b) False 

The correct answer is on the next page. 
Knowledge Check Answer 

Module 2, Slide 67

The correct answer is "a" – True. 

As you can see from the illustration on Slide 61, a Type I luminaire will spread light 

along a narrow roadway. (See Module 2, Slide 61)
Luminaire Poles 

Module 2, Slide 68

The next portion of this module will review considerations for poles used in lighting 

systems. 
Pole Types 

Module 2, Slide 69

There are many pole types onto which roadway luminaires can be mounted. Luminaires 

are often mounted to wooden or other types of utility poles. The picture above shows 

several types and configurations of poles specifically designed for mounting luminaires. 
Pole Design 

Module 2, Slide 70

 AASHTO wind map. 

AASHTO (the American Association of State Highway and Transportation Officials) 

produces a publication called Standard Specifications for Structural Supports for 

Highway Signs, Luminaires and Traffic Signals. These specifications are applicable 

to the structural design of supports for highway signs, luminaires, and traffic signals. 

The specifications are intended to serve as a standard and guide for the design, 

fabrication, and erection of these types of supports. 

This publication applies wind speed based on the AASHTO wind map (seen at left). 

Poles, foundations and anchor bolts designed by a structural engineer, must meet the 

requirements for the various regions based on wind speed. 

Factors to consider in pole design and selection include, wind loading (MPH), shape 

(round or square, straight or tapered), effective projected area (surface area) and 

weight. 
Breakaway Devices 

Module 2, Slide 71

 

 Top: Breakaway devices. Bottom: Example of what happens when a vehicle strikes a 

breakaway pole. 

Use a breakaway design to reduce the impact severity of sign supports and poles 

whenever feasible. 

Locate poles where they are less likely to be struck (e.g., further from the roadway, 

along the inside of curves, or behind existing barrier). 

However, if a breakaway device is located on a downward slope, that slope should be 

6:1 or flatter. Placing a breakaway device on a steeper slope may result in a vehicle 

striking the pole too high to activate the release mechanism at its base. 

When none of the above options are practical, a traffic barrier or impact attenuator may 

be required. 

Check the AASHTO Roadside Design Guide for more information on breakaway 

devices (link on slide 85). 
Lighting Controls 

Module 2, Slide 72

The next section of this module will discuss controls for roadway lighting systems. 
Photosensors 

Module 2, Slide 73

 

 

The most basic type of lighting control for street and roadway lighting is a photosensor. 

The photosensor provides an on-off switching response. It turns roadways lights on at 

dusk, and turns them off the next morning at dawn. The typical arrangement for these 

devices is to have one photosensor on the top of each luminaire controlling only that 

individual luminaire, although photosensors can be configured to control a group or 

zone of luminaires with one device. 

The failure mode for photosensors is always in the “on” position. In other words, if the 

photosensor fails, the luminaire will remain on 24 hours per day, until someone comes 

and replaces the photosensor. Photosensors are typically faced toward the north so that 

direct sunlight does not fall on the photocell within the device. There is also typically a 

time delay between the period when light levels are sensed as low enough to turn the 

roadway luminaire on, or high enough to turn it off. This prevents the sensor from 

turning the lights on and off continuously at dusk and/or dawn. 

Photosensors typically will last at least 10 to 15 years under normal operation, but you 

should check the manufacturer’s specification for the particular device you are 

purchasing. 
Astronomical Time Clocks 

Module 2, Slide 74

An astronomical time clock is used to turn on a group of luminaires on at a preset time 

each night, and off at a preset time each morning. 

It is called “astronomical” because it tracks the seasons of the year and will turn 

luminaires on earlier in the winter, when it gets dark earlier; and later in the summer. 

The time clock can also be adjusted to vary light levels at preset times during the night, 

for example, dimming the lights down after midnight when traffic volume in an area 

decreases, and raising it back up an hour before dawn when it increases again. 

These devices are commonly used for parking lot lighting, but are less likely to be used 

to control street and roadway lighting, except as part of a larger, networked control 

system. 
Occupancy Sensors 

Module 2, Slide 75

 

 Left: An outdoor occupancy sensor. Right: An example of the field of view of an outdoor 

occupancy sensor. 

Most occupancy sensors used for outdoor lighting are PIR (passive infrared) devices 

which sense the movement of heat (such as a person or a car) through a “field of view” 

for the sensor. These devices can either be integrated directly into a luminaire or 

mounted elsewhere, such as on a luminaire pole. Occupancy sensors work in 

conjunction with dimming ballasts or drivers to dim down luminaires during time periods 

when no motion is detected. 

While occupancy sensors can work well for parking lots, their use for roadway lighting is 

more challenging. If an occupancy sensor were used for roadway lighting it would need 

to be part of a networked system. An occupancy sensor, for example, could be placed 

at each access point on a roadway. Once it sensed motion there, it would send a signal 

through the network to other luminaires on the roadway to turn them up to full light 

output. Then, if no motion were sensed by any of the sensors along that roadway for a 

period of time (e.g., 15 minutes) the occupancy sensors would send a signal to dim the 

lights down again. 

You should not put non-networked occupancy sensors on each individual luminaire 

along a roadway because each luminaire will not turn on until a car approaches the field 

of view of its sensor. This will likely be annoying and distracting for drivers, and will not 

provide the amount of light needed for the driver to see very far ahead on the roadway. 
Networked Control Systems 

Module 2, Slide 76

 

Two illustrations of networked control systems. 

A centralized or networked control system allows you to operate and receive feedback 

from all devices on the system (sensors, light fixtures) from one central location. These 

systems either are wired, sometimes using the power lines to communicate to sensors 

and light fixtures, or, more frequently, they are wireless, allowing multiple devices to 

communicate using a radio frequency, Wi-Fi, or cellular signals. At their simplest, these 

centralized or networked systems are comprised of three main components: 

A Centralized Control through which you communicate with all devices on the network, 

set-up and commission these devices, make any changes, and collect information back 

from the devices so that you can monitor the system. Some systems have “cloudbased” services that host data and assist in the operation of the system.

A Gateway(s) is the device through which the central controller communicates with all of 

the other parts of the system. You will need at least one gateway, or multiple gateways 

for larger distributed systems. On some systems the central controller communicates 

directly with the end point luminaires via a cellular network, so a gateway is not needed. 

The Control Nodes are those devices (typically luminaires and sensors) that are being 

controlled. These are the end use devices that perform the commands as set up on the 

system. 
Adaptive Roadway Lighting 

Module 2, Slide 77

 

IES Recommended Practice (RP-8) for Roadway Lighting allows for the use of adaptive lighting 

throughout the night as pedestrian class and/or traffic volume is reduced. For example, using 

the chart above, if a study showed that on an expressway after midnight, the pedestrian class of 

the roadway reduced from “high” to “low”, the light levels could be reduced from 1 cd/m2 to 0.6 

cd/m2. 

Similarly, if the traffic volume of a roadway reduced after 1:00 AM allowing it to drop from the 

designation of a “major” road with medium pedestrian conflict to a “collector” road with low 

pedestrian conflict, the light levels could be reduced from 0.9 cd/m2 to 0.4 cd/m2, as shown in 

the chart above. 

Adaptive roadway lighting varies light level automatically and precisely in response to changes 

such as the level of pedestrian use or traffic volume on a roadway at night. This is typically done 

by first conducting a study on a roadway to determine the traffic volume and level of pedestrian 

conflict by hour, and then using a control system to dim the lighting on the roadway as either or 

both factors change over the night. This can also be done by use of an occupancy sensor, 

although that is less common. 
Adaptive Roadway Lighting (continued) 

Module 2, Slide 78

 

 Traffic volume on a roadway by hour, over a 12-hour nighttime period. 

As a further example of the use of adaptive lighting, look at the chart to the left. This 

chart shows that 61% of traffic volume occurs during the busiest four hours of the 12-

hour night. This heaviest traffic volume occurs from 19:00 to 21:00 hours (7:00 to 9:00 

PM) and after 6:00 AM in the morning. Based on research showing the relationship 

between traffic volume and crash frequency (Donnell et al., 2009, "Analysis of Safety 

Effects for the Presence of Roadway Lighting," Report to the National Cooperative 

Highway Research Program), we can estimate that 50% of crashes would be expected 

to happen during this 4-hour period. 

If a municipality wanted to use lighting during the times it would provide the most “value” 

in terms of crash reduction, it could provide more light during these hours, and reduce 

light levels over the remainder of the night. 
Self-Assessment Quiz

Module 2, Slides 79 to 86

Please answer each question. 

1. The average rated life of an HPS lamp can be up to ______. 

a.  40,000 hours of operation 

b.  20,000 hours of operation 

c.  60,000 hours of operation 

d.  100,000 hours of operation 

2. True or False? Plasma lighting systems are generally no more efficient than 

other types of HID lighting systems. 

a.  True 

b.  False 

3. When replacing an HID lamp with a screw-based LED replacement lamp you 

should consider ________. 

a.  how the LED lamp will alter the light distribution of the luminaire 

b.  the amount of heat that will build up within the luminaire 

c.  the light output of the LED replacement lamp 

d.  all of the above 

4. True or False? In order to control glare from a roadway luminaire, limit the 

amount of backlight emitted by the luminaire. 

a.  True 

b.  False 

5. Light trespass and sky glow are both considered to be components of _______. 

a.  a quality roadway lighting design 

b.  useful light for lighting the roadway 

c.  light pollution 

d.  an ecologically sensitive lighting design 

6. True or False? The IES Recommended Practice for Roadway Lighting (RP-8) 

allows for roadway lighting to be dimmed as the traffic volume or pedestrian class 

of a roadway changes over the night. 

a.  True 

b.  False 

See the following page for the answer key to this self-assessment. 
Self-Assessment Quiz Answer Key 

Module 2, Slides 79 to 86

The correct answers for the self-assessment are provided below. 

1. The average rated life of an HPS lamp can be up to ______. 

 a.  40,000 hours of operation (see Module 2, Slide 12)

 b.  20,000 hours of operation 

 c.  60,000 hours of operation 

 d.  100,000 hours of operation 

2. True or False? Plasma lighting systems are generally no more efficient than other 

types of HID lighting systems. 

 a.  True (see Module 2, Slide 31) 

 b.  False 

3. When replacing an HID lamp with a screw-based LED replacement lamp you 

should consider ________. 

 a.  how the LED lamp will alter the light distribution of the luminaire 

 b.  the amount of heat that will build up within the luminaire 

 c.  the light output of the LED replacement lamp 

 d.  all of the above (see Module 2, Slides 48-49) 

4. True or False? In order to control glare from a roadway luminaire, limit the amount 

of backlight emitted by the luminaire. 

 a.  True 

 b.  False (see Module 2, Slide 60) 

5. Light trespass and sky glow are both considered to be components of _______. 

 a.  a quality roadway lighting design 

 b.  useful light for lighting the roadway 

 c.  light pollution (see Module 2, Slide 60) 

 d.  an ecologically sensitive lighting design 

6. True or False? The IES Recommended Practice for Roadway Lighting (RP-8) 

allows for roadway lighting to be dimmed as the traffic volume or pedestrian class 

of a roadway changes over the night. 

 a.  True (see Module 2, Slide 76) 

 b.  False 
Extended Example Problem

Complete the empty cells in the following table: 

Light 

Source 

Efficacy 

(lm/W) 

Life 

(hours) 

Correlated 

color 

temperature 

(K)

Color 

rendering 

index 

(CRI)

Lumen 

maintenance 

(%)

Warmup time 

(min.) 

Restrike 

time 

(min.) 

High 

pressure 

sodium 

(HPS) 

24,000-

40,000 

1900-

2100 21-30 80% 10 1-2 

Mercury 

vapor 

(MV) 

25-58 16,000-

24,000 

3900-

5900 60% 5 3-10

Metal 

halide 

(MH) 

44-164 5000-

40,000 

2900-

5000 55-95 60%-

80% 5-20

Low 

pressure 

sodium 

(LPS) 

100-178 18,000 1700 0 90% 7-15 instant 

Plasma 50-110 3,000-

50,000 70-95 70%-80% 2-6 2-6 

Induction 47-88 60,000-

100,000 

2700-

5000 80 70% instant 

Light 

emitting 

diode 

(LED) 

60-140 30,000-

85,000* 60-90 * instant instant 

*LED life is for roadway lighting systems. Life is defined at the point where lumen 

maintenance reaches 70%. 

See the following page for the answer to this extended example problem.
Extended Example Problem (Answer Key)

Light 

Source 

Efficacy 

(lm/W) 

Life 

(hours) 

Correlated 

color 

temperature 

(K)

Color 

rendering 

index 

(CRI)

Lumen 

maintenance 

(%)

Warmup time 

(min.) 

Restrike 

time 

(min.) 

High 

pressure 

sodium 

(HPS) 

64-160 24,000-

40,000 

1900-

2100 21-30 80% 10 1-2 

Mercury 

vapor 

(MV) 

25-58 16,000-

24,000 

3900-

5900 15-50 60% 5 3-10

Metal 

halide 

(MH) 

44-164 5000-

40,000 

2900-

5000 55-95 60%-

80% 4-6 5-20

Low 

pressure 

sodium 

(LPS) 

100-178 18,000 1700 0 90% 7-15 instant 

Plasma 50-110 30,000-

50,000 

3200-

7650

70-95 70%-

80% 2-6 2-6 

Induction 47-88 60,000-

100,000 

2700-

5000 80 70% instant instant 

Light 

emitting 

diode 

(LED) 

60-140 3,000-

85,000* 

2900-

6500

60-90 * instant instant 

*LED life is for roadway lighting systems. Life is defined at the point where lumen 

maintenance reaches 70%. 
Links to Other Resources 

Module 2, Slide 87 

FHWA Lighting Handbook 

https://safety.fhwa.dot.gov/roadway_dept/night_visib/lighting_handbook 

IES RP-8 Roadway Lighting 

https://www.ies.org/store/recommended-practices-and-ansi-standards/roadway-lighting

LRFD Specifications for Structural Supports for Highway Signs, Luminaires, and 

Traffic Signals, 1st Edition 

https://bookstore.transportation.org/Item_details.aspx?id=2369 

AASHTO Roadside Design Guide 

https://bookstore.transportation.org/collection_detail.aspx?ID=105

Mogul Base LED Replacement Lamps 

https://www.bpa.gov/EE/Technology/EE-emerging-technologies/Projects-ReportsArchives/Documents/Mogul_LED_Lamps_LRC_BPA_Phase1_finalNov24.pdf

Lighting Answers: Plasma Lighting Systems 

http://www.lrc.rpi.edu/programs/nlpip/lightingAnswers/plasma 

Design Criteria for Adaptive Roadway Lighting 

https://www.fhwa.dot.gov/publications/research/safety/14051/14051.pdf 
Credits 

Module 2, Slide 89

Slide 69: Image courtesy of Virginia Tech Transportation Institute, WSP Global Inc., and 

DMD & Associates Ltd. 

Slide 70: From Standard Specifications for Structural Supports for Highway Signs, 

Luminaires, and Traffic Signals, 2009, by the American Association of State Highway 

and Transportation Officials, Washington, DC. Used by permission. 

Slide 71: Photograph courtesy of Virginia Tech Transportation Institute, WSP Global 

Inc., and DMD & Associates Ltd. 

Slide 76: Upper image courtesy of Virginia Tech Transportation Institute, WSP Global 

Inc., and DMD & Associates Ltd. 

All other images taken from U.S. Government publications or are released to the public 

domain by the module authors.