Light Emitting Diode Taxiway Edge 

Lights Emissions Evaluation 

Holly M. Cyrus

March 2005 

DOT/FAA/AR-TN05/10 

This document is available to the public through the National 

Technical Information Service (NTIS), Springfield, Virginia 22161. 

U.S. Department of Transportation 

Federal Aviation Administration

o

t

e t

e

c

h

n

i

c

a

l n

o

t

e t

e

c

h

n

i

c

a

ote technical note technic

a
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 the contents or use 

thereof. The United States Government does not endorse products or 

manufacturers. Trade or manufacturer's names appear herein solely 

because they are considered essential to the objective of this report. This 

document does not constitute FAA certification policy. Consult your local 

FAA airports office as to its use. 

This report is available at the Federal Aviation Administration William J. 

Hughes Technical Center’s Full-Text Technical Reports page: 

actlibrary.tc.faa.gov in Adobe Acrobat portable document format (PDF). 
Technical Report Documentation Page 

1. Report No.

DOT/FAA/AR-TN05/10 

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

5. Report Date 

March 2005

4. Title and Subtitle

LIGHT EMITTING DIODE TAXIWAY EDGE LIGHTS EMISSIONS 

EVALUATION 6. Performing Organization Code

ATO-P 

7. Author(s)

Holly M. Cyrus 

8. Performing Organization Report No.

DOT/FAA/AR-TN05/10 

9. Performing Organization Name and Address

Federal Aviation Administration 

William J. Hughes Technical Center 

Airport and Aircraft Safety 

10. Work Unit No. (TRAIS)

Research and Development Division 

Airport Technology Branch 

Atlantic City International Airport, NJ 08405 

11. Contract or Grant No.

12. Sponsoring Agency Name and Address

U.S. Department of Transportation 

Federal Aviation Administration

13. Type of Report and Period Covered

Technical Note

Office of Aviation Research 

Washington, DC 20591 

14. Sponsoring Agency Code

AAS-100 

15. Supplementary Notes

Messrs. Paul Jones, Jim Patterson, and Donald Gallagher of the FAA William J. Hughes Technical Center; and Messrs. Tom 

Paprocki, Jim Newman, and Ozzy Valdivieso of Hi-Tec Systems; and Messrs. Jess Nadel and Jim McGonigle of Consultant 

Services International Inc. provided technical support throughout the course of the evaluation. 

16. Abstract

This study was conducted to evaluate taxiway edge fixtures using light emitting diode (LED) technology to determine (1) if 

electrical emission levels from these fixtures are sufficient to cause interference to airfield circuits and warrant further 

investigation and (2) if there is a need to change the certification requirements for these electrical emissions. 

Five LED fixtures from different manufacturers were tested. The airfield lighting test bed located at the William J. Hughes 

Technical Center was used to measure the emissions of the fixtures. 

Electrical emissions occur in two forms, harmonic and nonharmonic. Harmonics are a distortion of the normal electrical 

frequencies emitted by the LED fixtures, which can cause problems with other equipment. Multiple electronic devices on a 

circuit, all emitting similar harmonics, can be additive and disruptive to the power distribution network. Harmonic emissions can 

cause voltage variations and overheating of the airfield circuit wiring. Nonharmonic emissions are a result of the circuitry in the 

power supply, which causes frequencies that are multiples of the power supply switching frequency. This can cause interference

on the electrical circuit. The current certification requirements contain procedures to test for emissions, with the lowest frequency 

being 150 kHz. 

The data from this study showed that four out of five fixtures had significant emissions that could possibly cause interference. 

These emissions were at a frequency as low as 12 kHz, which is much lower than the current certification requirements of 150 kHz, 

and warrants a change in the certification requirements. 

17. Key Words

LED, Light emitting diode, Taxiway edge light, Emissions, 

Harmonics 

18. Distribution Statement

This document is available to the public through the National 

Technical Information Service (NTIS), Springfield, Virginia 

22161.

19. Security Classif. (of this report)

Unclassified 

20. Security Classif. (of this page)

Unclassified 

21. No. of Pages

39 

22. Price

Form DOT F1700.7 (8-72) Reproduction of completed page authorized 
TABLE OF CONTENTS 

Page 

EXECUTIVE SUMMARY vii 

INTRODUCTION 1

Objective 1

Related Documents 1 

BACKGROUND 1

EVALUATION 2

Method 2 

Current Requirements 2 

Harmonic Emissions 3 

Fixture Efficiency 3 

Effects of Harmonics on Communications 3 

Nonharmonic Emissions 5 

Airfield Lighting Circuit Test Bed 5 

Controlled Source Impedance—Use of Line Impedance 

Stabilization Network 6 

Equipment 8

Nonharmonic Emissions Test Procedures 8 

Test Environment Definitions 10 

Measurement of Harmonic Emissions 12 

Measurement of Nonharmonic Emissions 14 

Harmonic Emissions Screen 15 

Nonharmonic Emissions Screen 15 

Results 16

Baseline Circuit Measurements 16 

Fixture A 18 

Harmonic Measurements 18 

Nonharmonic Measurements 18 

iii
Fixture B 19 

Harmonic Measurements 19 

Nonharmonic Measurements 20 

Fixture C 23 

Harmonic Measurements 23 

Nonharmonic Measurements 24 

Fixture D 26 

Harmonic Measurements 26 

Nonharmonic Measurements 26 

Fixture E 28 

Harmonic Measurements 28 

Nonharmonic Measurements 28 

Other Characteristics 29 

DISCUSSION 29

Fast Rise Time Distortion 29 

Harmonic Emissions 29 

Nonharmonic Emissions 29 

Power Factor Issues 30 

Capacitive Nature of Load 30 

Compatibility Detection of Operational Lamp Status 30 

Fixture Setting Brightness Based on Circuit Current 31 

CONCLUSION 31

iv
LIST OF FIGURES

Figure Page 

1 Harmonic Analysis Sample Screen 4 

2 Nonharmonic Spectrum Sample Screen 4 

3 MIL-STD-461E LISN Design 6 

4 MIL-STD-461E LISN Impedance Characteristics 7 

5 Project Test Bed Design 9 

6 Test Bed LISN Impedance 10 

7a Fixture A Total Harmonic Distortion 12 

7b Fixture B Total Harmonic Distortion 12 

7c Fixture C Total Harmonic Distortion 13 

7d Fixture D Total Harmonic Distortion 13 

7e Fixture E Total Harmonic Distortion 13 

8 Nonharmonic Emission Test Setup 14 

9 Baseline Harmonics—No Fixtures 17 

10 Baseline Spectrums 17 

11 Fixture A Harmonics, 2.8 amps 18 

12 Fixture A Spectrum, 2.8 amps 19 

13 Fixture B Harmonics, 2.8 amps 19 

14 Fixture B Even and Odd Harmonics Detail 20 

15 Fixture B Spectrum, 2.8 amps 21 

16 Fixture B Spectrum, 4.1 amps 21 

17 Fixture B Spectrum, 4.8 amps 22 

18 Fixture B Spectrum, 5.2 amps 22 

19 Fixture B, 5.2 amps, With Shifted Emission Frequency 23 

20 Fixture C Harmonics, 2.8 amps 23 

21 Fixture C Spectrum, 2.8 amps 24 

22 Fixture C Spectrum Close View 24 

23 Fixture C Emission Close Look at the Time Domain 25 

24 Fixture C Emission Frequency and Harmonics 26

25 Fixture D Harmonics, 2.8 amps 27 

26 Fixture D Spectrum, 2.8 amps 27 

27 Fixture E Harmonics, 2.8 amps 28 

28 Fixture E Spectrum, 2.8 amps 28 

LIST OF TABLES 

Table Page 

1 Equipment 8 

2 Decibel to Current Conversion 11 

v
LIST OF ACRONYMS

ac Alternating current

A-SMGCS Advanced Surface Movement Guidance and Control System

CCR Constant current regulator 

CENELEC European Committee for Electrotechnical Standardization 

CISPR International Special Committee on Radio Interference 

dB Decibel 

dBμA Decibel microamps 

dBA Decibel amps 

dBmA Decibel milliamps 

dc Direct current 

EUT Equipment under test 

FAA Federal Aviation Administration 

FCC Federal Communications Commission 

IEC International Electrotechnical Commission 

LED Light emitting diode 

LISN Line impedance stabilization network 

PC Personal computer 

R&D Research and development 

RGL Runway guard lights 

THD Total harmonic distortion 

vi
EXECUTIVE SUMMARY

This study was conducted to evaluate taxiway edge fixtures using light emitting diode (LED)

technology to determine (1) if electrical emission levels from these fixtures are sufficient to 

cause interference to airfield circuits and warrant further investigation and (2) if there is a need to 

change the certification requirements for these electrical emissions. 

Five LED fixtures from different manufacturers were tested. The airfield lighting test bed

located at the William J. Hughes Technical Center was used to measure the emissions of the 

fixtures. 

Electrical emissions occur in two forms, harmonic and nonharmonic. Harmonics are a distortion 

of the normal electrical frequencies emitted by the LED fixtures, which can cause problems with 

other equipment. Multiple electronic devices on a circuit, all emitting similar harmonics, can be

additive and disruptive to the power distribution network. Harmonic emissions can cause

voltage variations and overheating of the airfield circuit wiring. Nonharmonic emissions are a 

result of the circuitry in the power supply, which causes frequencies that are multiples of the 

power supply switching frequency. This can cause interference on the electrical circuit. The 

current certification requirements contain procedures to test for emissions, with the lowest 

frequency being 150 kHz. 

The data from this study showed that four out of five fixtures had significant emissions that 

could possibly cause interference. These emissions were at a frequency as low as 12 kHz, which 

is much lower than the current certification requirements of 150 kHz, and warrants a change in the 

certification requirements. 

vii/viii
INTRODUCTION

The Airport Technology Research and Development (R&D) Branch in response to a request

from the Office of Airport Engineering Division undertook this project to evaluate the effects on 

existing lighting circuits caused by the use of light emitting diode (LED) technology for airport 

taxiway edge lighting. This research will assist in the revision of advisory circulars (AC) 

concerning airport taxiway edge lights. 

OBJECTIVE. 

This effort evaluated LED taxiway edge lights to determine (1) if emission levels are sufficient 

to cause interference to airfield circuits and warrant further investigation and (2) if there is a need

to change the requirements for these emissions. The evaluation looked for harmonic distortion 

and nonharmonic emissions on five LED taxiway edge lights. 

RELATED DOCUMENTS. 

Related documents dealing with this evaluation project are: 

• Federal Aviation Administration (FAA) Advisory Circular 150/5340-24, “Runway and 

Taxiway Edge Lighting System,” September 3, 1975. 

• FAA Advisory Circular 150/5345-46B, “Runway and Taxiway Light Fixtures,” 

September 1, 1998. 

• FAA LED Engineering Brief, Light Sources Other Than Incandescent and Xenon for 

Airport and Obstruction Lighting Fixtures, Alvin Logan, AAS-100, March 2004. 

BACKGROUND 

LED-based airfield lighting fixtures are being installed on an increasing number of airfields. 

Initially, these fixtures were limited to obstruction lighting, which used some colors that were

more readily produced by LED components. Also, with obstruction lights, the size of the 

package and the number of LEDs were not critical. The next, logical place to implement LEDs

was for taxiway edge lights. This came as a result of the blue LED becoming a practical

component. 

In the last 10 or so years, with the increased number of airports going to low visibility operations

(Advanced Surface Movement Guidance and Control System (A-SMGCS)) or simply adding

runway guard lights (RGL) to improve awareness of runway entrances, the use of addressable 

devices has been increasing since a high percentage of in-pavement RGLs use some form of 

addressable device. These devices use communications on the series circuit to synchronize the 

flashing of the lights in a hold bar, and also use communications on the circuit to collect status of

the fixtures to ensure the operational state is known. 

Looking at the emissions requirements, the only standard in place is Federal Communications 

Commission (FCC) Part 15. As will be discussed below, Part 15 does not deal with the 

1
characteristics of the series circuit or the application of airfield lighting components. This 

project investigated the emissions produced by LED taxiway edge lights to determine if 

sufficient emissions are present to warrant further investigations. 

EVALUATION

METHOD. 

CURRENT REQUIREMENTS. The FAA LED Engineering Brief for Alternate Light Sources

provides additional requirements for LED fixtures. This document refers to FCC Part 15, 

Subpart B, covering unintentional radiators. The document (December 2003 rev) states that: 

• It is questionable if LED airfield fixtures can be classified by FCC Part 15, Subpart B. 

Airfield fixtures do not fall into the categories described by Part 15 B. 

• For radiated emissions, if the strictest interpretation of any equipment classification is 

used, the lowest frequency of concern is 30 MHz. 

• There is another radiated emission category for equipment that is designed to conduct 

their radio frequency emissions via connecting wires or cables and that operate starting in 

the frequency range of 9 kHz (for example, a communications cable or sensor that is on a 

cable assembly). However, these LED airfield fixtures are not designed for this purpose, 

on the contrary they are, or should be, designed not to radiate. 

• The fixtures that were part of the airfield equipment certification program were classified 

as a Class A device and tested for nonharmonic emissions with the lowest frequency of 

concern being 150 kHz. 

• There is a general requirement that applies to all equipment or equipment that cannot be 

classified by Subpart B. This requirement is in a different subpart which applies mainly 

to Subpart A, Section 15.5: 

Section 15.5 General conditions of operation. 

(b) Operation of an intentional, unintentional, or incidental radiator is subject to

the conditions that no harmful interference is caused and that interference 

must be accepted that may be caused by the operation of an authorized radio 

station, by another intentional or unintentional radiator, by industrial, 

scientific and medical (ISM) equipment, or by an incidental radiator. 

• There is no consideration to the cable plant in which the fixtures are installed.

Frequently, there are miles of cable configured in an open loop, which can provide a 

suitable radiating environment to other cables or into free space. 

2
The general statement of, “no harmful interference is caused,” refers to the fact that equipment

shall not cause other equipment to function improperly. But in the case of unclassified 

equipment, FCC Part 15 does not specify any quantitative numbers or elaborate on test 

procedures. 

With this very basic and general requirement in mind and since there is equipment on the airfield 

that is affected by frequencies below the FCC limits for classified equipment, suitable 

methodology must be developed to provide meaningful requirements for these products and the 

means to test compliance. 

The methodology in MIL-STD-461E, Requirements for the Control of Electromagnetic 

Interference Characteristics of Subsystems and Equipment, provides a basis for a more

meaningful test methodology and the means to adapt the testing environment to best suit the 

application. This is probably the best fit for the project since it guides the designer with the basis 

for setting up a proper test environment while recognizing the need to customize it for the

specifics of the system, where the product will be installed. This is covered in detail in the 

paragraph titled Conducted Noise Test Methodology. 

Generally, there are two categories of effects that these fixtures are likely to produce: 

• Harmonic Emissions 

• Nonharmonic Emissions 

HARMONIC EMISSIONS. 

Fixture Efficiency. The power supplies in these fixtures include switching elements that 

result in a nonlinear load to the series circuit. The net result of these effects is that harmonic

distortion reduces the efficiency of the fixture, possibly to the point of having a poor power 

factor, which will waste a portion of the power consumed by the fixture. The efficiency of LED 

fixtures is one of the advantages in implementing the technology. 

Effects of Harmonics on Communications. Generally, the power supply in some LED 

fixtures feature the charging of a capacitor that is switched in or out at a peak of nearly 60-Hz

current conduction. This is easily seen in the waveforms presented in figures 1 and 2. This 

portion of the conduction cycle on a conventional incandescent circuit has, in the past, been 

relatively free from noise. The switching action of this charging produces sudden changes in the 

current into the fixture, at a time when data transmission is occurring. Excessive harmonics 

produced at this time will degrade the communications of power line carrier products by a strong 

harmonic of sufficiently high frequency passing through the receiving circuitry of a remote 

device or modem in the lighting vault. 

An example of this case is the following situation: An LED fixture is plugged into a 

remote switching device as part of an airfield circuit. This switching device is in communication 

with the equipment in the lighting vault. The signal levels this device receives from the vault,

while still well within the usable range, are somewhat weak. In this situation, an LED fixture is 

actually connected directly to this remote device. Even weak harmonic emissions from this 

3
fixture would appear to the fixture receiving hardware to be strong, since it is directly on its 

connector, and could easily interfere with the communications. Furthermore, these emissions 

will also couple on the series circuit, such that they can interfere with other circuits as well. 

FIGURE 1. HARMONIC ANALYSIS SAMPLE SCREEN 

FIGURE 2. NONHARMONIC SPECTRUM SAMPLE SCREEN 

4
Nonharmonic Emissions. In addition to harmonics of the 60-Hz power, there are emissions that

are present even in relatively low levels that are not harmonically related. These emissions are 

either rise time related, (a sharp step in current rich in spectral content) or possibly the result of 

step response-induced resonance anywhere on the circuit. The presence of these emissions at an 

inopportune frequency, even in relatively small amplitudes, can easily have the effect of 

interfering with communications present on the circuit or proximate circuits. The level of these

signals need only be in the sub-milliamp range to be visible to communications equipment. 

This study was broken into three tasks: 

1. Develop an airfield lighting test bed and electrical test methodology for LED 

taxiway edge lights. 

2. Provide quantitative nonharmonic emissions test results for current airfield 

lighting manufacturer’s LED taxiway edge light fixtures. 

3. Determine if the current emissions tests referred to in the Engineering Brief, AC 

150/5340-24 and AC 150/5345-46B, adequately addresses this level of emissions 

and recommend changes, if necessary. 

Airfield Lighting Circuit Test Bed. Since one of the measurements to be made involves 

relatively small signals, any test methodology employed must provide a quiet electrical 

background noise environment. It could be seen from the preliminary look at the fixtures in the 

laboratory, that matters of gain, noise, and grounding impacted the resulting noisy waveform. In 

addition, the test setup must present the equipment under test (EUT) with impedance that 

approximates the actual operating environment, or at least with one that is standardized and from 

which extrapolation to the actual environment is feasible. There are virtually unlimited numbers 

of circuit configurations that are combinations of individual lengths of cables and transformers. 

Also, cable layout, age of the components, transformer type, the amount of water in the conduits 

pull pits and manholes, and the location and amount of ground leakage are among the many 

significant factors that determine the electrical characteristics of the circuit. This situation is

complicated both by the wide variability of field power source impedances and of laboratory 

sources such as Variacs, transformers and constant current regulators (CCRs). If the EUT is 

tested with the incorrect source impedance at the frequencies in question, the measurements are 

of little value. When considering nonharmonic emissions of a fixture that is connected to the 

series circuit, the circuit characteristics as they would appear to the fixture must be determined. 

However, this electrical environment is variable. 

The requirement for both a quiet electrical environment and a controlled impedance 

means that characterization of a fixture must be done on an individual basis with a test setup 

configured for this purpose, rather than as a field test. In addition, if the test setup is based on 

industry-accepted methodology, it will provide credible results that can be used as a basis for

making recommendations for standards and work with industry to address the issue of 

compatibility. 

5
MIL-STD-461E, Requirements for the Control of Electromagnetic Interference

Characteristics of Subsystems and Equipment, includes standards for emissions quantities and

frequencies, including frequencies of interest, and provides a methodology for measurement. 

Perhaps the most important feature of this standard is that it provides for the methodology and 

test apparatus to be modified or customized to meet the specific needs of the test requirements. 

This is clearly the case for testing of airfield lighting products, since it is a unique environment. 

It should also be noted that for now it is probably more important to use a methodology 

based on this standard and determine the emission levels, rather than adopt MIL-STD-461E 

emission limits as a standard to be met by the equipment. The data collected will then be used as

a basis for determining the actual quantitative limits to be recommended. 

Controlled Source Impedance—Use of Line Impedance Stabilization Network. To 

provide a predictable environment to make nonharmonic emissions measurements the impedance 

that the fixture under test is presented with must be fixed and controlled. A line impedance 

stabilization network (LISN) provides this capability. Standard LISNs that are used to make 

measurements are not likely to be useful at the low frequencies of interest and when considering

that the environment in question is a series circuit. Off-the-shelf LISNs are generally designed

for parallel wiring as well as with a ground reference. In the series circuit world, the current in 

the loop is the predominant factor. 

A relatively simple LISN was designed and built for this test. The design goal was 

• to provide a 50-ohm source impedance to the fixture, and 

• to decouple the impedance characteristics of the power source feeding the fixture. 

The use of LISNs has historically involved compromises between effectiveness and 

cost/size constraints. LISN design is particularly difficult at very low frequencies, where 

component size and cost (particularly for inductors) becomes prohibitive. As a result, the 

industry has tended to accept degradation of the impedance level at low frequencies. Such 

degradation is apparent in the LISN design specified by MIL-STD-461E in figure 3 and its 

impedance curve in figure 4. 

FIGURE 3. MIL-STD-461E LISN DESIGN 

6
FIGURE 4. MIL-STD-461E LISN IMPEDANCE CHARACTERISTICS 

At frequencies in the 10 kHz range, the LISN inductive reactance is so small that the 

EUT essentially sees the incoming line impedance. At high frequencies, the impedance

approaches the design goal of 50 ohms. 

The LISN required for nonharmonic emissions by FCC Part 15 includes even less 

stringent performance requirements, because the measurements do not fall below 150 kHz. A 

wide variety of LISNs are commercially available, with many designed to meet the requirements 

of International Electrotechnical Commission (IEC) Standard International Electrotechnical 

Commission` (CISPR) 16-1. Several types claim to meet the requirements of that specification 

for less than 20 percent impedance degradation at 9 kHz, which represents a considerable 

improvement over the MIL-STD-461E circuit. Substitution of a CISPR-compliant 9-kHz unit is

desirable and in keeping with the flexibility of MIL-STD-461E and possible future extension of 

compliance testing to IEC or the European Committee for Electrotechnical Standardization

(CENELEC) standards. (The test setup to be described below effectively meets the 9-kHz 

standard without use of a separate LISN.) 

As in other power equipment, the actual operating impedance seen by the lamp 

electronics is likely to be highly variable; however, 50 ohms is a reasonable test value, since the 

characteristic impedance of the transmission line loss represented by the series loop wiring will 

be in the 50-ohm range. 

Tests using the CE101 methodology of MIL-STD-461E (Nonharmonic Emissions, Power 

Leads, 30 Hz to 10 kHz) involves the use of a current probe to measure the EUT emissions for 

comparison with the relevant limits. If the EUT emissions are voltage-limited, extremely high 

terminating impedance will result in falsely low current readings, while extremely low 

impedance will result in current readings that are higher than would be present at 50 ohms. 

7
For the methodology starting at 10 kHz and up, CE102 of MIL-STD-461E, voltage is 

measured across the nominal 50-ohm LISN output. If the actual LISN impedance is 50 ohms,

the corresponding current will be V/50 and a seamless transition from the current to voltage

measurement will apply. In view of the impedance characteristics of the MIL-STD-461E LISN 

in figure 4, it can be seen that this is obviously not the case and only marginally true for the 

CISPR variety. For initial evaluation purposes, it is better to extend use of the current 

measurement to 150 kHz to encompass the region of major concern. 

EQUIPMENT. 

All tests were performed at the FAA William J. Hughes Technical Center, Atlantic City, New 

Jersey, at the airfield lighting test bed. Table 1 shows the equipment used for this evaluation. 

TABLE 1. EQUIPMENT 

Equipment Supplier Model

Data Acquisition system National Instruments DAQ-6052E

Analysis Software National Instruments Labview 7.1, Signal Analysis 

package, Custom Applications 

Spectrum Analyzer Rohde and Schwarz FSH3 

LISN, series circuit CSI, Inc. 

Digital Trigger Signal Circuit CSI, Inc. 

Receiver AOR AR5000A +3B

Scope Fluke 123A

Current Probe, for trigger Fluke i200 

NONHARMONIC EMISSIONS TEST PROCEDURES. 

The region below 100 kHz is often not covered by commercial spectrum analyzers. The widest 

range (and very expensive) analyzers extend down to the 9 kHz CISPR limit, or even lower.

Since the gaps between 60-Hz harmonics are of interest, the resolution should extend to a 

fraction of 60 Hz, down to at least 10 Hz and preferably lower. Another problem with a sweepbased spectrum analyzer is that the frequencies that are displayed are the result of an averaging

over time and cannot take into account the actual emissions magnitude that occurs at discreet, 

short intervals of time. 

For the present application, an analog data acquisition card in conjunction with computer-based

spectrum analysis software was used. The National Instruments 6052E data acquisition system 

was used for the project. This product has a sampling rate of 333,333 samples per second, 

allowing measurements up to 166.667 kHz. The analog to digital converter has a resolution of 

16 bits, resulting in a dynamic range of greater than 90 dB (1 part in 65,536, or 216). This data 

acquisition system provides samples to a software analysis package that runs on a personal 

computer (PC). For this project, Labview with the signal processing toolkit was used to develop 

data acquisition and analysis applications. The sample files acquired are processed by the 

8
application that was developed to extract the frequency characteristics of the measurements. In

addition, a Rohde and Schwarz FSH3 spectrum analyzer was used to measure emissions above 

150 kHz. 

Successful measurement of small signals at the desired resolution depends on careful attention to 

the test setup isolation, grounding, and instrument coupling. These aspects are discussed below. 

The test setup for MIL-STD-461E operates the EUT directly from the line via LISNs (one 

network in each side of the line). However, the typical environment is likely to require

additional isolation from the line to measure at and below the 1-milliamp level. Furthermore, the 

low volts/milliamp output of most current probes, and their susceptibility to stray magnetic 

fields, may pose a problem that is best solved by the alternate method of sampling the current

across a known low resistance. 

For these measurements, a Variac was used to control the lamp current. This entire environment 

must be set up on a suitable ground plane consisting of a sheet of metal, with the only ground 

connection to the instrumentation shown in figure 5. Layout and cable routing must be designed 

with care to provide the best results.

Variac

Split Bobbin ,

 4:1

Electrostatic

 Shield, 1:1 10uF

50 Ohm

Data

Acquisition 

system

Fixture under test 1 Ohm

Sampling Resistor

Coax

Signal

conditioning

Triggering 

Hardware

Trigger

Clamp on

Current probe

Aluminum ground 

plane .

1 by 1.5 meters

Single bonding point ,

Local ground plane to

equipment ground 

reference

Electrostatic

shield connection

point

All equipment (except PC )

placed on the ground plane ,

but insulated

Firewire

120 VAC

Line Impedance 

Stabilization

Network, (LISN)

FIGURE 5. PROJECT TEST BED DESIGN 

9
The resistive sampling is shown in differential four-terminal form. A high degree of isolation 

from line noise is provided by the use of an electrostatically shielded transformer designed for 

this purpose. A second step down isolation transformer of split bobbin design is also used. The 

4:1 turns ratio helps with reducing the maximum of 120 volts present on the Variac to more like

30 volts, making it easier to control. Additionally, the split bobbin design inherently provides a 

large leakage inductance, which provides the important function of isolating the impedance of 

the power system from the impedance derived from the 50-ohm resistor and 10-μF capacitor 

high pass network shown in figure 5. This high pass network provides a known impedance 

characteristic that is presented to the EUT so that current measurements are made across the 

1-ohm resistor. The voltage developed across this resistor, in volts, represents the circuit current 

in amps. 

This approach has the additional benefits of permitting the use of direct connection of one side of 

the EUT circuit to a local ground plane through the sampling resistor, thus permitting current 

sampling with virtually zero common mode voltage. This LISN, which is outlined in the dashed 

area of figure 5, shows greatly improved low frequency response. The impedance characteristics 

are shown in figure 6. 

FIGURE 6. TEST BED LISN IMPEDANCE 

Also provided is a means to consistently trigger the data acquisition at a known time. A simple 

current probe is placed on one of the power leads, as shown in figure 5. A sample of the raw

current is passed through a signal conditioning circuit to provide a positive going pulse at the 

60-Hz rate. The phase relationship of this pulse to the zero crossing of the current is controlled

and very stable, to within about 100 microseconds. This will provide a stable phase coherent 

trigger source to ensure that the captured waveforms start at the same place, preventing jitter 

from noise. 

TEST ENVIRONMENT DEFINITIONS. There are many terms and conversions that come into 

play with these kinds of measurements. Generally, decibel (dB) measurements are used in the 

emissions world. The use of dB, which is a logarithmic scale, better allows the signals that are

10
very small to be compared to the signals that are very large. When using dB for this application, 

the units of dBA (decibel amps), dBmA (decibel milliamps), or dBμA (decibel microamps) will 

be used. 

The formula for dBA is: 

dBA=20*log(current, in amps) 

This means that 0 dBA is 1 amp, or a measurement of 6 dBA is about 2 amps. The rule of thumb 

is an increase of 6 dB is about twice the magnitude. Considering the formula, a signal that is 20 

dBA stronger than another signal is in fact 10 times the amplitude. Or a signal that is weaker 

than another signal by -40 dBA is 100 times weaker in magnitude. 

The use of dBmA or dBμA simply changes the reference, such that 0 dBmA is 1 milliamp, and 0 

dBμA is 1 microamp. These are used for convenience to better fit the scaling to the application. 

Table 2 is a lookup table that can be used to convert current to dBA and vice versa. 

TABLE 2. DECIBEL TO CURRENT CONVERSION 

For dBA (decibel Amps) dBA = 20 * LOG(CURRENT) 

dBuA dBmA dBA uA dBuA dBmA dBA uA dBuA dBmA dBA mA dBuA dBmA dBA Amps

0 -60 -120 1 40 -20 -80 100 80 20 -40 10 120 60 0 1

1 -59 -119 1.11 41 -19 -79 112.2 81 21 -39 11.22 121 61 1 1.12

2 -58 -118 1.25 42 -18 -78 125.9 82 22 -38 12.59 122 62 2 1.25

3 -57 -117 1.41 43 -17 -77 141.3 83 23 -37 14.13 123 63 3 1.41

4 -56 -116 1.58 44 -16 -76 158.5 84 24 -36 15.85 124 64 4 1.58

5 -55 -115 1.77 45 -15 -75 177.7 85 25 -35 17.78 125 65 5 1.77

6 -54 -114 1.99 46 -14 -74 199.5 86 26 -34 19.95 126 66 6 1.99

7 -53 -113 2.23 47 -13 -73 223.9 87 27 -33 22.39 127 67 7 2.23

8 -52 -112 2.51 48 -12 -72 251.2 88 28 -32 25.12 128 68 8 2.51

9 -51 -111 2.81 49 -11 -71 281.8 89 29 -31 28.18 129 69 9 2.81

10 -50 -110 3.16 50 -10 -70 316.2 90 30 -30 31.62 130 70 10 3.16

11 -49 -109 3.54 51 -9 -69 354.8 91 31 -29 35.48 131 71 11 3.51

12 -48 -108 3.98 52 -8 -68 398.1 92 32 -28 39.81 132 72 12 3.98

13 -47 -107 4.47 53 -7 -67 446.7 93 33 -27 44.67 133 73 13 4.46

14 -46 -106 5.01 54 -6 -66 501.2 94 34 -26 50.12 134 74 14 5.01

15 -45 -105 5.62 55 -5 -65 562.3 95 35 -25 56.23 135 75 15 5.62

16 -44 -104 6.31 56 -4 -64 631 96 36 -24 63.1 136 76 16 6.31

17 -43 -103 7.07 57 -3 -63 707.9 97 37 -23 707.9 137 77 17 7.07

18 -42 -102 7.94 58 -2 -62 794.3 98 38 -22 79.43 138 78 18 7.94

19 -41 -101 8.93 59 -1 -61 891.3 99 39 -21 89.13 139 79 19 8.91

dBuA dBmA dBA uA dBuA dBmA dBA mA dBuA dBmA dBA mA 140 80 20 10

20 -40 -100 10 60 0 -60 1 100 40 -20 100

21 -39 -99 11.22 61 1 -59 1.12 101 41 -19 112.2

22 -38 -98 12.5 62 2 -58 1.25 102 42 -18 125.9

23 -37 -97 14.13 63 3 -57 1.41 103 43 -17 141.3

24 -36 -96 15.85 64 4 -56 1.58 104 44 -16 158.5

25 -35 -95 17.78 65 5 -55 1.77 105 45 -15 177.8

26 -34 -94 19.95 66 6 -54 1.99 106 46 -14 199.5

27 -33 -93 22.39 67 7 -53 2.23 107 47 -13 223.9

28 -32 -92 25.12 68 8 -52 2.51 108 48 -12 251.2

29 -31 -91 28.18 69 9 -51 2.81 109 49 -11 281.8

30 -30 -90 31.62 70 10 -50 3.16 110 50 -10 316.2

31 -29 -89 35.48 71 11 -49 3.54 111 51 -9 354.8

32 -28 -88 39.81 72 12 -48 3.98 112 52 -8 397.1

33 -27 -87 44.67 73 13 -47 4.46 113 53 -7 446.7

34 -26 -86 50.12 74 14 -46 5.01 114 54 -6 501.2

35 -25 -85 56.23 75 15 -45 5.62 115 55 -5 562.3

36 -24 -84 63.1 76 16 -44 6.31 116 56 -4 631

37 -23 -83 70.79 77 17 -43 7.07 117 57 -3 707.9

38 -22 -82 79.43 78 18 -42 7.94 118 58 -2 794.3

39 -21 -81 89.13 79 19 -41 8.91 119 59 -1 891.3

11
MEASUREMENT OF HARMONIC EMISSIONS. A Labview measurement application to 

graphically plot harmonics of the fixture current was developed for this project. The setup is

shown in figure 5. The current for the fixture was set to each of the 7 current steps that are used

with both 3- and 5-step CCRs. When the application runs, the software on the PC enables the 

data acquisition system. For these measurements, the system takes samples at the rate of

333,333 samples per second, or about 1 sample per 3 microseconds. In real time, the system 

then acquires the samples, captures them to the PC memory, and then the application software

shows the waveform in the time domain. The software also provides a graphical depiction of the 

strength of the number of harmonics desired and does the calculation for total harmonic

distortion (THD) of the waveform. The detailed measurements for each fixture and each current

step is shown in figures 7a through 7e, showing total distortion harmonics for each fixture. 

2.8

3.4

4.1

4.8

6.6

5.2 5.5

0

1

2

3

4

5

6

7

8

9

10

024 6 8

Fixture Current

% THD

Total Harmonic

Distortion (THD)

%

FIGURE 7a. FIXTURE A TOTAL HARMONIC DISTORTION 

4.1

6.6

5.5

5.2

2.8

3.4

4.8

0

2

4

6

8

10

12

0 2 468

Fixture Current

% THD

Total Harmonic

Distortion (THD) %

FIGURE 7b. FIXTURE B TOTAL HARMONIC DISTORTION 

12
6.6

5.5

5.2

2.8

3.4 4.8

4.1

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 2 4 6 8

Fixture Current

% THD

Total Harmonic

Distortion (THD) %

FIGURE 7c. FIXTURE C TOTAL HARMONIC DISTORTION 

6.6

5.5

5.2

2.8 3.4

4.8

4.1

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 5 10

Fixture Current

% THD

Total Harmonic

Distortion (THD)

%

FIGURE 7d. FIXTURE D TOTAL HARMONIC DISTORTION 

6.6

5.2 5.5

2.8

3.4

4.8 4.1

0

2

4

6

8

10

12

0 5 10

Fixture Current

% TH

D

Total

Harmonic

Distortion

(THD) %

FIGURE 7e. FIXTURE E TOTAL HARMONIC DISTORTION 

13
MEASUREMENT OF NONHARMONIC EMISSIONS. The measurements for the higher 

frequencies and lower levels of signals were done in a slightly different way. As shown in figure 

8, there is an additional high pass filter included in between the sampling resistor and the data 

acquisition system. By attenuating the 60 Hz by 40 dB or a factor of 100, the gain amplifier on 

the data acquisition system was set to be more sensitive, allowing single-bit resolution of about

3 microamps, placing the noise floor at about -50 dBmA, and this is more or less what is 

observed in figure 1. 

Variac

Split Bobbin ,

 4:1

Electrostatic

 Shield, 1:1 10uF

50 Ohm

Data

Acquisition

system

Fixture under test 1 Ohm

Sampling Resistor

Coax

Signal

onditioning 

Triggering 

Hardware

c

Trigger

Clamp on 

Current probe

Alumi

pl

 1 by

num ground 

ane .

1.5 meters

Single bonding point ,

Local ground plane to

equipment ground 

reference

Electrostatic

shield connection 

point

All equipment (except PC )

placed on the ground plane ,

but insulated

Firewire

120 VAC

Line Impedance 

Stabilization

Network, (LISN)

High Pass

Filter

-40 dB

(attenuat

factor of

--3db at

(fact

at 60 Hz

ion of a 

100), and 

6000 Hz

or of 0.7)

FIGURE 8. NONHARMONIC EMISSION TEST SETUP 

The spectrum analysis application running on the PC captured the samples running at the 

maximum rate of 333,333 samples per second, and first displayed them on the time domain 

window in the upper left of figure 2. 

The special feature of this application is that it must be recognized that the emissions actually 

can occur at different discreet times during the alternating current (ac) cycle. Merely placing the

signal into a spectrum analyzer or using a very wide window does not characterize the nature of

the emission. The application used here allows a cursor to be placed on the time domain

captured waveform, and a spectral analysis is done only on a defined window of the sample. 

This allows one to see that for some fixtures, the emissions are different at different parts of the 

ac cycle. 

14
The portion of the time domain that is being analyzed is displayed in the lower left window. In 

that window, a closer look of the time domain signal can be seen. In the lower right window, the 

spectrum view displays the amount of current, at specific frequencies. 

It also must be noted that the frequency characteristics of the high pass filter are compensated in

the frequency domain displayed in the lower left of figure 2. The inverse of the formula that 

characterizes the high pass filter frequency response is applied to the signal levels at the 

frequencies involved, thus normalizing as a function of frequency amplitudes at about 6 kHz 

HARMONIC EMISSIONS SCREEN. A sample screen of a harmonic measurement is shown in 

figure 1. The upper right window shows the input signal under test, which was captured from 

the data acquisition system. The current waveform is shown and is presented in amps. 

Highlighted in red is the calculation of THD. The lower right window labeled Exported Signal 

Spectrum shows the amount of spectral energy at the specific harmonic frequencies shown. 

Harmonics are shown in dBA. Typically, the fundamental of 60 Hz is the first signal seen, and 

in this case, the cursor is shown at the 60-Hz position, with strength of 9.13 dBA, displayed in 

the numerical window under the spectrum trace. In this case, 9.13 dBA is a little more than 2.8 

amps, which is approximately the current step for this example; the odd harmonics are 

predominantly seen here, at the next peak (after 60 Hz) at 180 Hz. 

NONHARMONIC EMISSIONS SCREEN. This screen provides the detail for emissions of 

frequencies that are not necessarily harmonically related to 60 Hz see figure 2). For these 

measurements, the current sample is passed through a high pass filter before entering the data 

acquisition system. This high-pass filter has attenuation at 60 Hz of 40 dB or about a factor of 

100. This was done to allow more resolution of smaller signals, by increasing the gain of the 

data acquisition system input amplifier, without overloading it. This filter also has the effect of 

shifting the phase of 60 Hz by about 90 degrees lagging or about 4.33 milliseconds. The higher 

frequencies are not phase shifted.

For this reason, an external trigger, which starts the data acquisition at the actual zero crossing of 

the current, is used. Looking at the time domain waveform in the upper left of the screen, the 

white trace is the current sample through the high-pass filter. A synthesized 60 Hz can also be

seen in green on that window. The synthesized signal starts at the real zero crossing and has no 

effect on any measurement. Its purpose on the screen is to provide a reference for viewing the 

actual phase of the 60-Hz signal. A cursor is also visible on the same window. This cursor is 

used to locate a selected sample area of which to perform the spectrum analysis. This allows

specific spectrum characteristics to be identified at specific locations in time. The yellow cursor

is the start of the sample and the red cursor is the end of the sample to be examined. In this 

example, the cursor is placed in a location where there is an emission of relatively high strength.

It appears on the white waveform to be just before the peak of the 60-Hz signal, but because of 

the phase shift in the 60 Hz, referring to the green synthesized waveform, it can be seen that this 

high frequency is in fact just after the peak of the 60-Hz signal. 

The lower left window, Selected Sample Waveform, is a “zoom in” of what is bounded by the 

cursors in the Raw/Filtered Waveform above it. Depending on the waveform, this can be

additionally zoomed in both in time and amplitude to allow a close look at the signal in time.

15
The axes are labeled in amps and time. In the lower right window, the exported signal spectrum

shows the frequencies present in the selected sample waveform. There is compensation in the

magnitude of the frequencies displayed to account for the roll off characteristics of the high pass

filter used for this measurement. The strength of the frequencies is shown in dBmA, where a 

signal of 0 dBmA is equal to 1 milliamp. In this example, there is a signal at 15.625 kHz at a 

little more than 0 dBmA, followed by its harmonics at 31.250, 46.875, 62.500, 78.125 kHz, etc. 

The filtering area is used to place a software digital filter of configurable design in line with the

incoming signal. This is not used for signal measurements but for analysis of the effects of the 

signal waveforms on typical filters used in the front end of the receiving hardware, to see what 

these systems would have to contend with if these emissions are present on the circuit.

RESULTS. 

BASELINE CIRCUIT MEASUREMENTS. Before measurements on the fixtures were 

conducted, a baseline of the system without fixture was conducted. There is always a level of 

harmonics and other emissions present in the incoming power system. Passing it through the 

Variac and isolation transformers will generally reduce ground-related noise; however, there is a

residual characteristic that is seen in figures 9 and 10. Odd harmonics characteristics are seen no 

stronger than -40 dBA and below 1 kHz. Harmonics are below the -70 dBA range. This is

typical of what is seen of power through the magnetics of transformers. Figure 9 also shows the 

total harmonic distortion, on the order of 0.4%. While this is not absolutely perfect, it is well 

below THD that will be seen as a result of the fixtures. The spectrum measurement in figure 10 

shows in the domain view the small bend in the current that is exaggerated by the high pass 

filter. This is the characteristic of core magnetization in the transformers and must be kept in 

mind for the rest of the samples. Also, it shows that there is a background of extremely small

spectral components, the strongest of which are in the -35 dBmA range or about 20 microamps; 

not a significant factor for these measurements. Fixtures from five current lighting 

manufacturers were obtained for testing and were labeled A-E. 

16
FIGURE 9. BASELINE HARMONICS—NO FIXTURES 

FIGURE 10. BASELINE SPECTRUMS 

17
FIXTURE A. 

Harmonic Measurements. Refer to figure 11 for the 2.8-amp step for the harmonic 

measurement of this fixture. The THD can be seen in figure 7a. This fixture shows a step 

characteristic near the peak of the current, resulting in a worst-case THD of about 9% at 

2.8 amps. Even so, there are odd low-order harmonics that are below -40 dBA (10 mA) before 

they reach the 13th harmonic and are near -70 dBA at about 2.0 kHz. When the current is 

stepped up to 6.6 amps, the lower harmonics (which contained more energy at lower step) drop 

off more rapidly while the higher-order harmonics are of similar strength, resulting in the THD 

of only 1.7%. 

FIGURE 11. FIXTURE A HARMONICS, 2.8 amps 

Nonharmonic Measurements. The emissions spectrum is shown in figure 12. For the 

most part, no nonharmonic emissions, except the low-order harmonics, are seen. Generally, the 

-50 dBmA noise bed is seen with some consistent unrelated low-level peaks in the -40 dBmA

range (10 microamps). 

18
FIGURE 12. FIXTURE A SPECTRUM, 2.8 amps 

FIXTURE B. 

Harmonic Measurements. Refer to figure 13 for the 2.8-amp step for the harmonic 

measurement of this fixture. The THD is shown in figure 7b. THD on this fixture actually 

increases from about 10% at 2.8 amps to more than 11% at 4.1 amps, and then down to about 3% 

at 6.6 amps. 

FIGURE 13. FIXTURE B HARMONICS, 2.8 amps 

19
Besides the odd harmonic content, this fixture also has substantial even harmonics that can 

be seen on the captures in figure 14. The even harmonics subside, as the constant current

regulator step, is increased while the odd harmonics stay more or less the same. An illustrative 

plot of this is included in figure 14 for clarity. Some even and odd harmonics are labeled. 

Typically, even harmonics are caused by asymmetry of the signal that is there, which is a 

residual direct current (dc) component from more current being drawn during one half of the 

cycle than the other half of the cycle. This can frequently be caused by an internal half wave

rectifier power supply. 

21

-87

-80

-60

-40

-20

0

Frequency (Hz)

-18 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 2992

Exported Signal Spectr

1

8

0 3

0

0

um (dBA)

1

2

0 2

4

0

6

0

8

0

6

0

0

0

4

5

4

0

4

2

0

3

6

FIGURE 14. FIXTURE B EVEN AND ODD HARMONICS DETAIL 

Nonharmonic Measurements. The emissions spectrum is shown in figure 15. This 

fixture showed a varied set of characteristics. Looking through the spectrum figures, it can be

seen that there are high frequency emissions that are present during a majority of the time on the 

ac cycle. Furthermore, the frequencies change as a function of the current setting. The 

characteristic of this emission in the time domain is shown very well in figure 16 at a step of 4.1 

amps. A portion of the time domain signal is expanded in the selected sample waveform

window in the lower left of the image. This shows a characteristic impulse shape with a peak-topeak value of around 10 milliamps. This impulse type emission includes strong even and odd 

harmonics of nearly equal magnitude. This can be seen in the selected sample spectrum window. 

The fundamental of this frequency is around 15 kHz, with harmonics across the board of the

window up to 156 kHz and higher. 

At 4.8 amps in figure 17, the frequency of the emission changes to about 52 kHz, with a 

similar impulse shape and also about 10 milliamps peak to peak in magnitude. It shows odd and

even harmonics at 104 and 156 kHz. 

In figure 18, the frequency changes again, to a fundamental of about 39 kHz, and still 

includes odd and even harmonics. 

20
Also noteworthy on the same current step, the emissions changed characteristics slightly

later in the ac cycle, shifting up in frequency to about 42 kHz, as shown in figure 19. 

FIGURE 15. FIXTURE B SPECTRUM, 2.8 amps 

FIGURE 16. FIXTURE B SPECTRUM, 4.1 amps 

21
FIGURE 17. FIXTURE B SPECTRUM, 4.8 amps 

FIGURE 18. FIXTURE B SPECTRUM, 5.2 amps 

(Frequency changes during cycle) 

22
FIGURE 19. FIXTURE B, 5.2 amps, WITH SHIFTED EMISSION FREQUENCY 

FIXTURE C. 

Harmonic Measurements. Refer to figure 20 for the 2.8-amp step for the harmonic

measurement of this fixture. The THD is shown in figure 7c. This fixture showed THD between 

about 1% and 2% between 2.8 and 6.6 amps. The distortion, while low, showed its lowest 

distortion at 2.8 amps, and its highest at 5.2 amps. 

FIGURE 20. FIXTURE C HARMONICS, 2.8 amps 

23
Nonharmonic Measurements. The emissions spectrum is shown on figure 21. A closer 

look at the selected sample spectrum for this fixture reveals nothing remarkable until the highest 

detectable frequency is reached—166.666 kHz. At that frequency, the signal strength increases 

to 2.3 dBmA. A closer look at the frequency being measured in the time domain reveals that the 

sampling rate of 333.333 kHz is showing a maximum and minimum on every sample taken, 

meaning the actual frequency and magnitude must be measured another way. This is shown in

figure 22. The Selected Sample Waveform looks triangular because each point is right on a 

sample, with no points in between. 

FIGURE 21. FIXTURE C SPECTRUM, 2.8 amps 

FIGURE 22. FIXTURE C SPECTRUM CLOSE VIEW

24
A further investigation with the Rohde and Schwarz FSH-3 Spectrum analyzer reveals

that the signal is in fact about 168 kHz, just beyond the reach of the data acquisition system (see 

figure 23). Not only are the emissions of high frequency and at about the 2 dBmA range, the 

presence of harmonics is visible, and they can be seen at multiples of 160 kHz, up past 1.8 MHz 

at -6.3 dBmA. Another view reveals that these harmonics are measurable to about 5 MHz. The 

presence of even and odd harmonics, which are of similar strength, indicates that one is dealing

with impulse radiation that occurs at the 168-kHz rate and possess a fast rise time. Figure 23 

shows that the waveform in the time domain taken with a Fluke 199 in fact displays the impulse 

characteristic. This shows the pulses separated by about 6 microseconds, which nearly 

corresponds to 166.666 kHz. This does not exactly match the 168 KHz on the other view 

because the frequencies exhibit some jitter and will never exactly correlate. 

The sample seen with the Fluke are showing about 20 mA peak-to-peak magnitude. The

scaling in the legend does not include the fact that a 1:1 probe was used (see figures 23 and 24). 

FIGURE 23. FIXTURE C EMISSION CLOSE LOOK AT THE TIME DOMAIN 

25
FIGURE 24. FIXTURE C EMISSION FREQUENCY AND HARMONICS

FIXTURE D. 

Harmonic Measurements. Refer to figure 25 for the 2.8-amp step for the harmonic 

measurement of this fixture. The THD is shown in figure 7d. The THD for this fixture ranged 

from a low of 0.8% to a high of 1.6% at 5.5 amps. Primarily, low-order odd harmonics rapidly 

subsided to about -70 dBA at about 2 kHz at the higher steps and to lower at the lower steps. 

Harmonic emissions were for the most part unremarkable. 

Nonharmonic Measurements. The emissions spectrum is shown in figure 26. This 

fixture showed quiet operation across the board with no detectable spectral emissions. Only the 

noise bed is visible on the image. 

26
FIGURE 25. FIXTURE D HARMONICS, 2.8 amps 

FIGURE 26. FIXTURE D SPECTRUM, 2.8 amps 

27
FIXTURE E. 

Harmonic Measurements. Refer to figure 27 for the 2.8-amp step for the harmonic 

measurement of this fixture. The THD is shown in figure 7e. This fixture ranged from a high of 

9.8% THD at 2.8 amps to a low of 4.4% at 6.6 amps. The harmonic content is primarily lowerorder odd harmonics, which achieves -70 dBA in the 3 kHz range. 

FIGURE 27. FIXTURE E HARMONICS, 2.8 amps 

Nonharmonic Measurements. The emissions spectrum is shown in figure 28. This 

fixture showed no continuous spectral emissions. Only the noise bed is visible on the image. 

There is, however, a significant step in the current profile. 

FIGURE 28. FIXTURE E SPECTRUM, 2.8 amps 

28
Other Characteristics. Fixture E included a fast rise time step in the current of about 40 

milliamps in 3 microseconds. 

DISCUSSION 

The data from this study showed four out of the five LED taxiway lighting fixtures had 

significant harmonic emissions and nonharmonic emissions. 

FAST RISE TIME DISTORTION. 

The emissions that were seen for the fixtures tested include both harmonic and nonharmonic

type. The harmonic emissions are characterized by disturbances in the current, where the current 

diverges from a pure sinusoid. This can also be stated as the disturbances that occur on each half 

cycle. A look at the waveforms captured in the time domain show that samples with higher 

harmonic distortion contain a more pronounced discontinuity in the current. In the case of 

discontinuities that have a steep rise time, there is an instantaneous peak in broadband energy. 

Mathematically, summing harmonically related sinusoids can generate a step in signal, or square 

wave. The reverse is also true; a step in the signal contains sums of harmonic sinusoids. With 

that said, current profiles that contain current steps have the potential of interfering with systems 

that operate at the frequencies that are components of those steps. 

HARMONIC EMISSIONS. 

Increased harmonic distortion at low currents for some fixtures reduces the power factor of these 

devices, which makes them less efficient. Efficiency is generally a desirable characteristic in

LED fixtures so this tends to reduce this advantage. 

Harmonic distortion in the fixture, particularly when it is a result of sharp steps in the current 

(such as in fixtures B and E), results in sharp discontinuity of the current. The receiving circuits 

used by addressable lighting systems generally use some kind of bandpass filter in the front end.

This step in current tends to make the bandpass filter ring at the frequency that is used for 

communications. These systems already contend with such a step from thyristor-fired regulators, 

but fixtures add a step of their own in a different portion of the ac cycle that has the potential of 

interfering with communications, reducing a clear area in the conduction cycle. 

NONHARMONIC EMISSIONS. 

As shown in the results (the other forms of emissions that are seen in the tests), frequencies range

from about 12 kHz to as much as 168 kHz. These emissions depend on the CCR step setting and 

which fixture is in use. Virtually all of these emissions are impulse type repeating at these high 

rates. They include both even and odd harmonics, which extend in some cases into the 

megahertz range. For this test activity, the primary issue was to make individual measurements

in a quiet, controlled laboratory environment to develop an understanding of exactly what the 

emissions are coming from each fixture. The real issue now is the effect of hundreds of fixtures 

on a series circuit. 

29
Even though the L830 transformers are in place at each fixture, the losses in these transformers is 

not that significant, individually. These have been measured in the order of -3 to -4 dB of loss, 

primary to secondary at about 150 kHz. In a situation where there is capacitive coupling of the 

series circuit, these losses may not attenuate the fixture emissions. It also must be considered 

that these emissions have the potential to be introduced in a long wire cable plant in which 

coupling to other cables has been seen in the field of these frequencies. 

Effects of harmonic and nonharmonic emissions on addressable devices with the emissions that 

have been measured at the LED fixtures, it must be kept in mind that these fixtures, in some

cases, could be plugged directly into an addressable device. This is not a design parameter of 

these units, and the introduction of a noise source locally into an addressable device is certainly 

something that should be investigated, as the levels measured in many cases are more than the 

normal signal levels under which these systems operate. The step discontinuity in the current

also will cause the receive circuitry to “ring” providing another source of interference. 

It is also possible that these emissions could crosstalk into proximate circuits in the same

conduits. This is in many ways related to the circuit layout and routing. 

POWER FACTOR ISSUES. 

With the harmonic distortion seen, it is likely that the power factor is also reduced to the mid 

80% range in some cases. This should be measured to include in-load calculation for new 

circuits. Most suppliers do not provide power factor numbers at lower steps, but only at the top 

step. 

CAPACITIVE NATURE OF LOAD. 

The power supply in some of these LED fixtures appears to have a switched capacitive front end. 

There have been cases where a capacitive load has caused certain CCRs to lose regulation by

false triggering of the thyristors. One is aware of cases where electronic components with 

similar capacitive front ends caused exactly this loss of regulation, causing a mass failure of all

components on a series circuit with currents in excess of 30 amps. 

COMPATIBILITY DETECTION OF OPERATIONAL LAMP STATUS. 

The input to the fixture is mostly designed as a power supply. While there is a requirement in 

the FAA engineering brief to provide a fail open function, the other side of the story is that these

devices must be able to detect that the fixtures are operational. With an incandescent fixture, this 

is a simple continuity test, but with a power supply front end, the impedance characteristics are 

wildly variable, depending on where in the 60-Hz cycle the detection function takes place. Also,

there are different methods for detection of a lamp operating, and these fixtures were not a 

design parameter. 

30
FIXTURE SETTING BRIGHTNESS BASED ON CIRCUIT CURRENT. 

During the test, it was observed on several occasions that many of the fixtures provided a preset 

step erratically depending on the current. It has been shown that the same fixture sometimes

went to a given step when the circuit current was on a nominal CCR step, and there were times

that the current was within the current step tolerance stated in AC 150-5345-10E for the same

step, but selected a different brightness setting. This raises the question of how all the fixtures 

will perform when subjected to a variety of current and circuit conditions, CCR waveforms, and 

transient events. The worst-case scenario is when some fixtures are at one step while others are 

at another step on the same circuit at the same time. 

CONCLUSION 

The data from this study showed four out of the five LED taxiway lighting fixtures had 

significant harmonic emissions and nonharmonic emissions. 

Further investigation of the LED taxiway light fixtures in a typical airfield lighting circuit is

required to understand what the conducted emissions will do to the other equipment in the 

circuit. Areas of investigation are: 

• Compatibility for communications. Develop an understanding of the impact of 

nonharmonic emissions has on other systems. 

• Transformer test. Determine what the different transformers power consumption is for 

each type of fixture. Determine whether or not using a smaller transformer does actually 

help. 

• Field measurements on a large circuit containing LED fixtures. Determine if emission

levels become more of a problem as size of circuit increases. 

• Fixture intensity setting performance. Determine what happens to fixtures during current 

changes at different intensity settings on a series circuit. 

• Detection of failed lamps. Characterize the way fixtures look electrically to a control

device. 

• Fixture Efficiency. Determine power efficiency of various LED lighting fixtures. 

Compares the actual power consumption to rated power consumption. 

31/32