CEDIA
WHITE PAPER
Dimming LED
Lamps White
Paper
© 2014 CEDIA
TABLE OF CONTENTS
01 Why LED Lighting? Comparison of Different Lighting Sources and Types
Advantages and Limitations of LEDs
IESNA Lighting Source Comparison chart
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5
02 Which LED Light? Important Aspects of Selecting Fixtures Certifications Performance Parameters
Environmental Impact
Warranty
6
6
6
6
6
03 LED Lighting Fixture Control Architecture
LED based lighting fixture
6
7
04 Why Dim LEDs?
Questions to Ask When Dimming an LED Lamp
Types of LED Products
Dimming Range
Dimming Performance
Control Technologies
Forward Phase Control
Reverse Phase Control
0-10V Control
DALI (Digital Addressable Lighting Interface)
DMX (Digital Multiplex Interface)
Number of Lamps on a Dimmer
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9
9
11
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11
12
12
12
12
13
05 Types of Controls and installation
Central Control System
Local Control
Installation of LED Lamps
Installation of LED Fixtures
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14
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06Conclusion
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07 Appendix A
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DIMMING LED LAMPS WHITE PAPER
ACKNOWLEDGMENTS
DEFINITIONS
Amanda Beebe – Lutron
Efficacy (LPW):
The overall system efficiency of a luminaire, which is
the total usable light output (given in lumens) divided
by the real electrical power input (given in watts).
Commonly referred to as “Lumens Per Watt,” or LPW.
Aussie Kizirian - Interior Technologies
Ken Byrd – Cree
ACRONYMS
CBCP
Center Beam Candlepower
CCT
Correlated Color Temperature
CFL
Compact Fluorescent Lamp
CRI
Color Rendering Index
DALI
Digital Addressable Lighting Interface
DMX-512
Digital Multiplex Interface
ELV
Electric Low Voltage
LED
Light Emitting Diode
LPW
Lumens Per Watt
MLV
Magnetic Low Voltage
UL
Underwriters Laboratories
INFORMATIVE REFERENCES
National Electrical Manufacturers Association LSD-49
Solid State Lighting for Incandescent Replacement Best Practices for Dimming
Illuminating Engineering Society of North America
Lighting Handbook, 9th Edition
Correlated Color Temperature (CCT):
The temperature of the black body, or Planckian
radiator, whose perceived color most closely resembles
that of a given light source at the same brightness and
under specified viewing conditions. Given in Kelvin (K).
Color Rendering Index (CRI):
The ability of a light source to reproduce the color of
various objects faithfully in comparison with an ideal or
natural light source.
LED Lifetime:
The number of operating hours that the LED can
maintain >70% of its original light output for a given
set of temperature and light flux conditions. Lifetime
is given as L70. (LEDs do not catastrophically fail like
incandescent or fluorescent lights. Instead, they get
progressively dimmer over a long period of time as
they are operated.)
Spectral Power Distribution (SPD):
The light power per unit area per unit wavelength of an
illuminating source. Given as a two dimensional graph,
with the x-axis being wavelength and the y-axis being
relative light power per unit area.
Power Factor (PF):
The ratio of real power to apparent power. Commonly
given as a percentage (%) or a two decimal number
(0.00).
Dimming Range:
Ratio of minimum to maximum measured light, usually
expressed as a percentage (%).
Driver:
Auxiliary device(s) needed to operate and vary the
intensity of light output from LED lamp source(s) by
regulating the voltage and current powering the source.
Measured Light:
Stated light level defined by a manufacturer.
© 2014 CEDIA
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DIMMING LED LAMPS WHITE PAPER
INTRODUCTION:
DOCUMENT SCOPE
The objective of this document is to educate the
reader regarding benefits, performances, correct
usage and limitations of Light Emitting Diode (LED)
lighting. The paper discusses available lamp types and
their characteristics (i.e., dimming range), are their
different power sources: external or internal drivers,
performance and LED dimmers.
Dimming LED lighting addresses the residential lighting
applications and technical requirements needed to
properly prepare wiring for LED fixtures. The paper
also compares LED lighting to other technologies that
are currently available in the market, with respect to
compatibility with control systems, photometry, light
quality, spectro-power distribution, expected life-span,
special installation requirements, source impedances
and line noise.
LED lighting for most applications meets all the
residential requirements in a satisfactory to superior
manner. This paper discusses the return on investment
(ROI), including greater efficiency, fewer hazards than
CFLs, cost effectiveness and increased visual appeal.
Additionally, this document contains a list of potential
questions the electronic system contactor (ESC)
should discuss with a client prior to system design.
The applications and information contained in this
document only refer to white LED lights and not
their RGB counterparts. Government rebates on LED
products are not covered, but may be discussed in a
future white paper. Differences between manufacturers
aren’t discussed either, although guidance is
provided on how to which identify manufacturers
meet the criteria of a job or an application. A list of
standards that govern the efficiency requirements and
performance of products is provided in the informative
references section.
The information provided in this document is for
educational purposes only and is not a CEDIA
endorsement of any manufacturer or product.
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© 2014 CEDIA
01 WHY LED LIGHTING?
A Light Emitting Diode (LED) is an electronic device
that produces light when an electrical current is
passed through it. The color of light that is emitted is
dependent on materials from which the LED is made.
LEDs are available in red, blue, amber, green and
near-UV colors, with lumen outputs ranging from 10 200 lumens. The LEDs used predominantly in general
illumination applications are “phosphor converted
blue” LEDs, which are blue LEDs that have a layer of
yellow phosphor placed over the chip. The phosphor
absorbs some of the blue light and emits yellow light.
When the unabsorbed blue light mixes with the yellow
light, it creates “white” light.
There are several advantages as well as limitations
in LEDs for general illumination purposes as seen in
the IESNA table below. LED-based lighting fixtures
can achieve efficacies ranging from 25 LPW to over
80 LPW, compared to an incandescent efficacy of
5-10 LPW. LEDs convert electrical energy to light
at an efficiency of ~30%, compared to <5% for an
incandescent, resulting in dramatically lower heat
produced. LEDs can also achieve useful lifetimes
ranging from 25,000 hours to >100,000 hours,
compared to ~1000 hours for an incandescent. In
addition, LEDs do not contain hazardous materials such
as mercury vapor found in siCFLs.
One of the limitation of LEDs are higher costs as high
brightness LEDs, necessary for general illumination,
are expensive. They also require electronic drivers
to convert conventional AC voltage to discrete DC
voltages for the LED arrays. These factors, combined
with special thermal design considerations, make
LED-based fixtures considerably more expensive.
Another is limited applications due to the constraints
of operating temperature environments, relative young
technology and a slower uptake. LED-based lighting
fixtures are not always available for every application
or aesthetic requirement. Lastly, the wide range of
LED-based lighting product types available means
not all LED lamps are dimmable, and the ones that are
can be limited in dimming performance and system
compatibility.
DIMMING LED LAMPS WHITE PAPER
Table 1: IESNA lighting source comparison chart
Some of the parameters of interest when comparing lighting sources are efficacy, quality and lifetime as shown in Table 1 above. Efficacy is expressed in LPW, which denotes lumens out per electrical watt in, light quality is expressed by color rendering index (CRI),
which is the ability of a light source to render every visible color in the spectrum and lifetime measures useful life of lamp in hours.
CRI
Starting
and Warmup time
(minutes)
Dimming
Range
(Percent
Light
Output)
Initial
Lumens
750
100
0
100-0
1690
20
2000
100
0
100-0
6000
90
14
2500
100
0
100-0
1280
High Output Fluorescent
(3000 K – 4000 K)
54
93
20,000
85
0
100-1
2900
Fluorescent
( 3000 K – 4100 K)
32
88
20,000
75
0
100-1
2800
Compact Fluorescent,
long twin
(3000 K-4100 K)
38
87
20,000
82
1
100-5
3300
Compact Fluorescent, double
(2700 K -4100 K)
26
70
10,000
82
1
100-5
1800
Mercury Vapor
(6800 K)
175
45
24,000
20
< 10
1000-10
7900
Metal Halide, low wattage
(3200 K)
100
81
10,000
70
<5
100-50
8075
Metal Halide, high wattage (4000
K)
400
90
20,000
65
< 10
100-50
36,000
HPS, low wattage
(2100 K)
70
90
24,000
21
<5
100-50
6,300
HPS, high Wattage
(diffuse)
250
104
24,000
21
<5
100-50
26,000
Source and Correlated
Color Temperature
Lamp
(Watts)
Efficacy
(LPW)
Life
(Hours)
Standard Incandescent Filament
(2700 K)
100
17
Tungsten – Halogen
(2950 K)
300
Tungsten – Halogen
(2850 K)
© 2014 CEDIA
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DIMMING LED LAMPS WHITE PAPER
02 WHICH LED LIGHT?
IMPORTANT ASPECTS FOR
SELECTING FIXTURES
Some important aspects such as certifications,
performance parameters and warranty, when selecting
LED lighting fixtures are discussed in this section.
Certifications one should be aware of are: Underwriters
Laboratories (UL) listed and compliant, California Title
24 Compliant, Department of Energy’s EnergyStar
Program Certification, and Illuminating Engineering
Society of North America (IESNA). California title 24 is
a high efficiency lighting program in effect in California
and Washington State. IESNA is the generally accepted
industry guidelines for measuring parameters of Solid
State Lighting (SSL) fixtures. Any LED-based lighting
fixture should be tested using IESNA guidelines to
ensure accurate data as described in Appendix A.
Performance parameters to look for when procuring
LED lighting fixtures are light quality, efficacy, power
factor and lifetime. Different white light sources have
different attributes and care should be taken in the
selection process to ensure the right source is used for
the right application. The most common measurements
of light quality are: correlated color temperature
(CCT) and color rendering index (CRI). The CRI of LED
based fixtures can vary from ~80 to ~95. For typical
phosphor-converted blue LEDs, CRI is generally
inversely proportional to efficacy, meaning that high
CRI translates into low LPW, and vice versa.
Efficacy becomes very important when there are
limitations on total power that can be consumed by
lighting. To make sure there is enough light for the
given power restrictions requires choosing a light
source with high LPW. Power factor (PF) is the ratio
between real power and apparent power. Apparent
power, which is what the power source sees, must be
supplied to a load. If the real power is substantially
lower, this results in power loss.
This is particularly important for commercial
applications where the local power company bills for
apparent power. Lifetime is another characteristic to
closely examine when selecting LED lighting. L70 is
the industry standard for stating lifetime and IESNA
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© 2014 CEDIA
has testing requirements on how it is to be measured
and calculated. The two main factors that affect it are
operating temperature and operating current. The
luminaire manufacturer should be able to provide
results from an independent third party testing
laboratory.
Environmental impact is another aspect to consider
when selecting a lighting fixture. It is important to
be aware if the lighting fixture is RoHS compliant
meaning it contains no toxins or toxic substances such
as mercury and/or lead, if the luminaire is made from
recycled or recyclable materials and if the fixture can
withstand the temperature and humid conditions of the
application.
Lastly, warranty is a critical aspect that should
be examined before procurement. The typical
industry standard is a three-year limited warranty
on manufacturing defects, although there are some
companies offering five-year warranties. The buyer
or specifier should ensure that the manufacturer has
the ability to back their warranty. The buyer should
also ensure that the fixture is compatible with existing
hardware and able to shed heat appropriately in
retrofit applications, is compatible with different
types of control and if the new fixture has a system of
“replaceable parts” for future upgrades.
03 LED LIGHTING FIXTURE CONTROL
ARCHITECTURE
The fixture usually consists of the following parts: LED
Array, Heatsink, Light Diffuser (optional) and Housing.
LED Array is the array or grouping of LED(s). In some
fixtures, it consists of one LED of a certain color, and
in others, several independent strings of different
colored LEDs. Heatsink is the primary heat dissipation
mechanism for the LED array. In certain fixtures, it
might be necessary that the heatsink be exposed to
convective airflow. Housing is the mechanical structure
that holds the other pieces together and typically
provides mounting brackets/supports. In addition, some
fixtures use direct emission of LEDs with no diffuser,
while others use a diffuser to mix different colors of
LEDs and/or create a “single point” light source.
DIMMING LED LAMPS WHITE PAPER
Figure 1: Sub-components of an LED Light Fixture
LED-based lighting fixtures consist of several sub-components. Different manufacturers will incorporate some or all of these sub-components into
a single unit. This means that some fixtures require an external LED driver and/or power supply, while others are completely integrated. The main
sub-components are demonstrated below in Figure 1.
Input Voltage
(120/277vac)
Power
Supply
Dimming
Interface
LED
Fixture
LED
Driver
•
•
•
•
LED Array
Heatsink
Diffuser
Housing
Dimming
Input
LEDs are discreet DC devices and, depending on the
array configuration, can require either one or several
discreet DC voltages to drive the particular LED
array. The LED Driver typically receives 12vdc, 24vdc,
32vdc or custom DC levels from the power supply.
The LED driver usually receives the dimming signal
from the dimming interface. Power Supply converts
the source power to the discreet DC level(s) required
by the LED driver. Depending on the fixture type, the
source of power can be 120, 230 or 277 VAC from a
line voltage source or 12vdc or 24vdc from a battery or
photovoltaic array controller.
Dimming Interface converts the dimming signal to
the proper signal required by the LED driver for
dimming operations. There are generally two types
of dimming inputs are Line Voltage or “Phase Cut”
and Low Voltage. In Line Voltage, the dimming
interface examines the alternating current waveform
and determines the level of dimming to be applied.
The most common dimmer types are Incandescent,
Magnetic Low Voltage (MLV), and Electronic Low
Voltage (ELV).
Incandescent is called a “leading edge” or “forward
phase” dimmer and is typically a SCR-based triac
device that cut the AC waveform on the leading edge.
Magnetic Low Voltage (MLV) is also a leading edge
dimmer. They are designed for inductive loads, like
magnetic dimming ballasts. Electronic Low Voltage
(ELV) are called “trailing edge” or “reverse phase”
dimmers and these are typically FET (field effect
transistor)-based devices that cut the AC waveform
on the trailing edge. They are designed for capacitive
loads, for example electronic dimming ballasts. Low
Voltage will be discussed in greater detail in the
Control Technologies section (page 14), but consist of:
0-10v, DMX, Digitally Addressable Lighting Interface
(DALI) and EcoSystem.
© 2014 CEDIA
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DIMMING LED LAMPS WHITE PAPER
Figure 2: LED Power Usage
The why dim story for LEDs is the same for fluorescent, incandescent and other conventional light sources. Dimming LEDs saves energy linearly.
This means that if you dim LEDs down to 50% of their light output you will save nearly 50% of your energy usage as seen in Figure 2. By dimming
LEDs, not only do you save with a more efficient source, you save even more energy.
LED Driver: Power vs. Measured Light
100%
90%
80%
70%
Power
60%
50%
40%
30%
20%
10%
0%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Measured Light
04 WHY DIM LEDS?
Dimming LEDs also makes them run cooler. Cooler
temperatures should extend the life of the electronic
components of the driver, as well as the phosphor, by
allowing them to run at a lower temperature. This will
extend their life, doubling or tripling the LEDs usable
hours. Dimming any lamp – incandescent, CFL or LED
enhances ambiance. Whether you are in a restaurant,
theater or presentation space, you can get the feeling
that the lighting designer intended. The home and the
workplace should be designed to address/adjust to
client needs. As client needs change throughout the
day, the lighting should adapt as well: bright to read a
book, but dim for computer use, for example. Lighting
control can create a comfortable atmosphere to
support activities throughout the day.
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© 2014 CEDIA
Lighting controls can enhance the safety and security
of a customer’s home as well. The customer can
control both interior and exterior lights from the car
as they approach the driveway to ensure optimal
visibility—and no more fumbling for the light switch
when unlocking the door. Lighting controls can even
connect to security systems to turn on lights in case of
an emergency. Dimmers installed by the stairs and in
hallways can illuminate a path of light in key areas of
the house making it easier to navigate from one room
to the other during the night.
Lighting control also increases productivity allowing
the user to select the level they need to reduce eye
strain and fatigue so that they can work at peak
performance
DIMMING LED LAMPS WHITE PAPER
A. QUESTIONS TO ASK WHEN
DIMMING AN LED LAMP
Before you commit yourself or your customer to
investing in LED technology you need to understand
its limitations, especially when it comes to
dimming control compatibility. Many LED luminaire
manufacturers are new to the lighting industry and
are not familiar with the multitude of control types
and the corresponding product design requirements
that accompany them. This has resulted in “dimmable”
products that do not work as claimed, flicker or
never completely turn off. These are major problems
that need to be addressed so that consumers do not
associate all LEDs with poor performance and become
averse to using them. High-performing LED products
do exist, but you need to ask the right questions to
make sure you have chosen one of those products
appropriately.
By using the five questions below as a guide, ESCs can
confidently purchase and install an LED fixture or lamp
and ensure all customer expectations are met.
1. What type of LED product am I using: LED lamp or
LED fixture?
2. What is the dimming range of the fixture?
3. What is the dimming performance of the product?
4. On what type of control does the LED product
operate?
5. What is the minimum or maximum number of
fixtures/lamps that can be connected to one
dimmer?
B. TYPES OF LED PRODUCTS
LEDs are inherently low-voltage devices. Therefore,
additional electronic components are required to
convert the line voltage power to low voltage for
the LEDs. These electronics may also interpret
control signals, and dim the LEDs accordingly. These
electronics are referred to as a driver. LED luminaires
come in two distinct types: LED bulbs (also called LED
is or retrofit lamps) and LED fixtures. LED bulbs have
Edison base sockets and are meant to replace standard
incandescent or screw-in CFL bulbs. LED bulbs have
integral drivers that determine if they are dimmable,
and if so, to what performance level. LED fixtures can
vary from cove lights to downlights and usually have
an external driver. Some fixture manufacturers offer
different driver options on the same fixture to support
different control technologies or applications (such as
dimmable vs. non-dimmable.)
There are two different types of LED drivers: constant
voltage types (usually 10V, 12V and 24V) or constant
current types (350mA, 700mA and 1A). Just as their
names would suggest, a constant current driver
provides a constant current, such as 700mA, to a permade LED array that is designed to operate at or below
that current level. A constant voltage driver provides a
constant voltage to one or more LED arrays connected
in parallel. These two types of drivers are NOT
interchangeable, and it is the design of the LED array
that determines which driver is appropriate. Often this
is based on application, but it is still the configuration
of the LED that determines if a constant current or a
constant voltage driver is needed.
A constant current LED driver allows for simpler LED
array design because multiple LEDs in a single array
are merely wired in series. However, it can only be used
with an LED array designed for the same or higher
current level. A 700mA light engine will work with
a 700mA driver, but you cannot connect additional
700mA loads to the same driver. This is great for a
downlight, sconce or other LED fixtures that use only
one light source per driver (much like a fluorescent
lamp with its associated ballast). Note that some
drivers support multiple currents, making them more
flexible when designing a fixture.
A voltage driver is used in areas where you may have
a variable amount of fixtures, such as a cove or undercabinet light. Here you can keep adding LED arrays
to the driver up to the driver’s maximum power limit.
These are similar and sometimes identical to electronic
or magnetic low voltage power supplies and often have
12V and 24V outputs.
Some drivers are manufactured to operate specific
LED devices or arrays, while others can operate most
commonly available LEDs. LED drivers are usually
compact enough to fit inside or on a junction box,
include isolated Class 2 output for safe handling of
the load, operate at high system efficiency, and offer
remote operation of the power supply. However, not all
drivers meet these criteria.
© 2014 CEDIA
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DIMMING LED LAMPS WHITE PAPER
Drivers with dimming capability can dim the LED light
output over the full range from 100% to 1% or less.
Dimming drivers can dim LEDs by reduction in the
forward current or pulse width modulation (PWM) via
digital control. Most dimming drivers operate using the
PWM method as seen in figure 3. With this method, the
frequency could range from a hundred modulations
per second to as high as hundreds of thousands of
modulations per second, so that the LED appears to
be continuously lit without flicker. The application will
determine whether a very high PWM frequency or
continuous current reduction (CCR) is needed as seen
in figure 4.
Compatibility is essential between the LED driver and
the control, whether the driver is built into the lamp
or is external to a fixture. For example, a 0-10V driver
must follow the same standards as the 0-10V control in
order for them to function together properly.
When using a control system, you may run into 0-10V
control devices and systems such as occupancy
sensors, photocells, wall box dimmers, remote controls,
architectural and theatrical controls, and building and
lighting automation systems. LEDs can also work with
devices governed by the DMX and digital addressable
lighting interface (DALI) protocols. In the future, they
may include wireless (RF) as a control option. The
driver has a wider range of possible control types
that are discussed in the Control Technologies section
(page 14).
One of the most important LED driver features to
examine is the quality of the DC output voltage of
the driver. To maximize the light output from the
LEDs without overstressing them requires a constant
DC current to be maintained. Additionally, the
instantaneous response of LEDs to changing current
makes them highly susceptible to flicker, especially
compared to incandescent sources. Finally, be
cautioned that remote mounting of the driver results
in potential voltage drops and power losses on the DC
wiring that must be properly accounted for.
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© 2014 CEDIA
PWM Dimming
Rated LED Current (or Voltage)
Driver Output
Current (or Voltage)
Time
Figure 3: PWM Dimming
CCR Dimming
Rated LED Current (or Voltage)
Driver Output
Current (or Voltage)
Time
Figure 4: CCR Dimming
DIMMING LED LAMPS WHITE PAPER
C. DIMMING RANGE
Incandescent lamps dim to below 1% perceived light,
which appears as the filament glow you are familiar
with. The dimming range of an LED lamp or fixture
could vary from one device to another. Some may
dim to a minimum level of only 50%, while a different
product may dim to 1%. Additionally, manufacturers
will quote measured light numbers, but consumers are
familiar with perceived light. What is the difference?
Measured light output is the quantifiable value of light
measured by a light meter or similar device. This is
the dimming percentage indicated on LED product
specification sheets. Perceived light is the amount of
light that your eye interprets due to pupil dilation. The
eye’s pupil dilates at lower light levels, causing the
amount of light to be perceived higher than measured
(i.e., 20% measured light equals 45% perceived light).
The equation for determining perceived light is to take
the square root of the measured light percentage (e.g.
√0.2 = 0.45).
You need to select the dimming range of your fixture
or lamp that will meet your expectations. A product
that dims to 20 percent measured light (45 percent
perceived) wouldn’t make sense in a media room, but
may be the energy-saving solution necessary for an
office.
D. DIMMING PERFORMANCE
Each manufacturer defines dimming in a different
way; what you need to know is if the dimming will be
distracting or will have noticeable unexpected drops
in light. The publics experience with incandescent
dimming is that it is smooth and continuous.
Specifically, a change in the control (dimmer) position
should be reflected by an equal change in light level.
There should be no abrupt change in light level as the
light source is being dimmed. Even more important
than smooth and continuous dimming is ensuring that
there are no points of flicker in the dimming range.
Flicker is the unexpected modulation of light level
that is visible to the human eye. Flicker can come
from many sources, including line noise, control noise,
component tolerance and LED driver circuit design.
Flicker can be continuous (happening all of the time),
or intermittent (only happening some of the time or at
certain light levels). A good lamp should account for
all of these factors and still provide flicker-free, smooth
and continuous dimming.
In addition, it is important to be aware of ambient
temperatures at the application. While LEDs have
the ability to start at temperatures as low as -40°C,
operating them at cold ambient temperatures can
cause operating problems. LEDs draw higher power
at cold ambient temperatures – the opposite of what
happens with fluorescent lamps – and can lead to
system malfunction. For outdoor applications where
the power supply is mounted remotely, the maximum
LED load on the driver should be de-rated by 10-20%
to avoid system conflicts during cold temperatures.
Another consideration is that customers don’t want
“pop on” in their lighting. The level the light is at when
it is turned off is the level the light should return to
when it is turned back on. There should be no dropout, so the light should only turn off when the switch is
turned off. This can be achieved by utilizing the low end
trim settings available on many wall box and system
level dimmers to ensure that the lights remain on at
their lowest light level at the bottom of the dimmer’s
travel. The light levels should change any time the
control is adjusted. Adjusting the control without a
corresponding change in light level is undesirable and
is referred to as “dead travel.”
E. CONTROL TECHNOLOGIES
The following control technologies refer to the signal
and wiring between the control on the wall and the
fixture or lamp. LED retrofit lamps generally use one
of two control technologies: forward or reverse phase
control methods. LED fixtures may use any method,
and are independent of the driver type (constant
current or constant voltage).
These control technologies are used in stand-alone
applications and control systems as well as in wired
and wireless lighting control systems. Controls that use
forward phase control to control a lamp may also use a
wireless technology to communicate among fixtures or
within an entire home lighting control system.
i. Forward Phase Control.
Typically used for incandescent and MLV light sources,
forward phase control is the most common method
of dimming control. NEMA estimates that there are
approximately 150 million forward phase control dimmers
installed residentially (NEMA LSD-49), and many of these
are bound to control LED replacement lamps.
© 2014 CEDIA
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DIMMING LED LAMPS WHITE PAPER
Working well with forward phase control is critical to
the success of LED bulbs because there are hundreds
of millions of forward phase dimmers already installed
for use with incandescent and halogen lamps.
Unfortunately, the controls were never designed for
LED lights and are not UL listed to operate LED lights,
so the performance is hit or miss and in many cases will
cause LEDs to flicker, drop out, pop on or not dim very
low. These dimming controls may also require multiple
lamps per control in order to meet the minimum load
requirements of the control.
standard. This leads to drivers and lamps that claim
to be 0-10V compatible, but instead drop out, pop
on or dim backwards with the lowest light at the top
of the control and the brightest light at the bottom.
Some 0-10V products do not work at all with controls
designed for 0-10V ballasts, which are the majority of
installed 0-10V commercial controls. Since the control
signal is a small analog voltage, long wire runs can
produce a significant drop in the signal level resulting
in varying light levels from different drivers controlled
by the same control device.
Please note that new forward phase control dimmers
have recently entered the market that have been
specially designed to reduce or eliminate the
problems seen with controlling LED loads on existing
incandescent dimmers.
iv. DALI.
This digital standard originated in Europe for control
of fluorescent ballasts, but is now commonplace in
commercial buildings in the United States. It is also
defined in IEC standard 60929 Annex E and allows for
digital control of individual fixtures, maximizing the
user’s control and productivity.
ii. Reverse Phase Control.
Typically used to control ELV light sources, reverse
phase control is best for capacitive loads such as LED
drivers. While it does not have the installed base that
incandescent dimmers possess, this control type is
more successful at high performance LED dimming
without flicker.
Reverse phase dimmers were designed for the lower
power “electronic loads” of electronic low voltage
transformers, so they tend to work better with the
drivers required for LED loads. Unfortunately, these
controls require a neutral wire to power the internal
electronics, and not every electrical back box has a
neutral present. Installing reverse phase dimmers in
older buildings may require that a neutral wire is pulled
to the box. Furthermore, these types of controls are
not as widely available in the marketplace.
iii. 0-10V Control.
This analog control standard has been used in energy
management controls such as occupancy and daylight
sensors and is now becoming popular with many LED
products. This control type is isolated and considered
low voltage class 2, enabling it to be safe to the touch
and allowing for simplified wiring.
One of the benefits of 0-10V controls is that it is
defined in the IEC (International Electrotechnical
Consortium) standard number 60929 Annex E.
Unfortunately, some manufacturers don’t follow the
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DALI provides addressing of individual fixtures and
status feedback from the drivers. This makes it easy to
digitally assign occupancy sensors, daylight sensors,
time clocks, manual controls and other controls to
one or many fixtures without complicated wiring. It
opens up an entire suite of energy-saving and systemmonitoring control schemes where the design and
setup is all done within software, making designing
with them simple. Some derivatives of DALI, such as
EcoSystem, further simplify the programming process
by allowing you to use a handheld device in the space
and not have to know details of the system, such as
fixture addresses.
v. DMX-512.
Typically used in theatrical applications, DMX remains
popular with RGB LED applications where multiple
channels are necessary for individual color control.
Some manufacturers are using DMX as the control
type for white light in general illumination applications,
which can often be complicated in terms of wiring,
addressing and interacting with other controls in the
space. Contact the manufacturer for more information
about how DMX controls can be integrated with control
systems. Integrating between general lighting control
systems and DMX fixtures can often be complicated.
A fixture and the desired control may use the same
control technology (ex: 0-10V) but it does not mean
DIMMING LED LAMPS WHITE PAPER
they will perform well together. This is especially true
with forward and reverse phase control, due to the lack
of a formal standard. Even control technologies that
have a standard only pertain to compatibility and do
not indicate anything about performance.
The only way to know for sure if an LED lamp or fixture
will work with a particular dimmer is to test them
before installation in the client’s home. Whether that
testing is a mock-up or testing by the manufacturer, it
is necessary to determine if flicker, pop-on, dead travel,
etc will occur. Keep in mind that you will not be able
to visually determine the inrush of an LED product.
Therefore, find out from the manufacturer or limit the
number lamps to avoid overloading the dimmer.
This transient electrical stress, among many other
reasons, may limit the maximum number of lamps
you can install on one dimmer. A minimum number of
fixtures may be required to operate a dimmer because
of the 25-watt to 60-watt minimum load that most
incandescent dimmers require to operate correctly
under all conditions. When using incandescent bulbs,
the minimum load requirement was easily met with
usually only a single bulb. However, with LEDs, four or
more loads may be needed on a dimmer in order to
meet the required minimum load.
Keep in mind this inrush stress only occurs on phase
control products (forward or reverse). The inrush
current is shown in Figure 5.
Many manufacturers (both LED luminaire
manufacturers and control manufacturers) conduct
compatibility testing of their products. It is up to you
to determine if a manufacturer’s assessment of “good
dimming” will meet client needs.
Inrush Current
F. NUMBER OF LAMPS ON A DIMMER
A common problem associated with LED system
operation is overloading the driver. LED drivers are
rated for a maximum load which must be given proper
attention. Connecting too many LEDs in series may
result in too low a voltage being available to the last
LED(s) in the chain. Similarly, some LED drivers may
not perform well if too little load is put on them. Using
a wrong voltage driver will cause the LEDs to either not
light up or operate at higher currents than intended. A
prudent practice is to check the voltage rating of the
LED load being used against the rated output voltage
of the driver. For example, using a 12V driver on a 10V
LED load could result in a significantly shorter life of
the module.
Turn on
Current
Voltage
Time
Figure 5: Inrush Current
The number of lamps to be installed on a single
dimmer may seem like an easy question to answer, but
it is not as simple as looking at a 600-watt dimmer
and dividing 600 by the 10-watt LED lamp selected.
This calculation yields that 60 lamps can be used on a
circuit and while the LED lamp may only draw 10 watts
continuously, there is a possibility of an inrush current
spike during every half-cycle. Neglecting this inrush
performance can put significant stress on the dimmer
and can cause premature product failure.
© 2014 CEDIA
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DIMMING LED LAMPS WHITE PAPER
05 TYPES OF CONTROL AND
INSTALLATION
Forms of lighting control include occupancy sensors,
daylight sensors, timeclock switches, a variety
of manual and automatic dimming devices, and
centralized controls. Some controls operate on line
voltage power, while others are low-voltage (DC)
powered.
a. Central Control System.
Centralized lighting control systems can be used to
automatically turn on, turn off, and/or dim lighting at
specific times or under certain conditions. This type
of control system can be used in an individual room or
an entire house. Centralized lighting control systems
can also be integrated with other home automation
systems, such as audio/visual systems, fire alarms and
security systems. Centralized lighting control systems
can be programmed to use a variety of inputs from
occupancy sensors, daylight sensors, timeclocks,
keypads, remotes, touch screens or other devices and
systems to trigger lighting events. A lighting control
system can simultaneously adjust groups of lights
to predefined levels to create the desired mood and
ambiance.
b. Local Control.
Local control is typically achieved by having individual
dimmers or lighting control devices directly controlling
the attached lamps or fixtures. Local controls can be
integrated with sensors or other inputs on a smaller
scale than a central control system or, in some cases,
can be integrated into the central control system.
c. Installation of LED lamps.
When installing a screw-in LED lamp, you may unscrew
the existing lamp and replace it with an LED lamp. Be
sure to check with your fixture’s manufacturer about
heat shedding compatibility. However, you may need
to replace the dimmer in order to have acceptable
dimming performance of the lamp. You can reference
the manufacturer’s packaging or website (for example
http://www.lutron.com/LEDtool) for information on
what dimmers are compatible with specific lamps. If
you are replacing a stand-alone wall box dimmer you
can often do this without an electrician. If the lamp is
on a system device, contact a dealer to determine what
product is best and how to install it.
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d. Installation of LED fixtures.
LED fixtures need to be installed by a licensed
electrician and require that they are installed with the
appropriate control device. Some of these fixtures
easily retrofit into existing wiring, while others require
more extensive renovations, depending on the
compatible controls. Keep in mind that interfaces may
be available to eliminate the need for wiring changes.
06 CONCLUSION
LEDs are a promising new light source for most
applications and dimming saves energy by reducing
the light level and electric power consumption. The use
of LEDs can lead to even greater savings compared
to incandescent bulbs because of its longer life-time,
greater efficacy and construction. It is necessary to
examine the LED luminaire’s specification sheet to
determine if the lighting is compatible with the control
system and the driver desired. In addition to energy
savings, dimming LEDs contributes to a soothing
ambiance in the home, which the customer is willing to
pay a premium for.
07 APPENDIX A
The following two procedures outline measurements
of SSL fixtures, components and modules using IESNA
guidelines:
1. LM-79-08. This approved method describes
the procedures and precautions for performing
reproducible measurements of total luminous flux,
electrical power, luminous intensity distribution and
chromaticity of solidstate lighting (SSL) products
for illumination purposes under standard conditions.
2. LM-80-08. This method allows a reliable
comparison of test results among laboratories by
establishing uniform test methods. It addresses the
measurement of lumen maintenance testing for
LED light sources, including LED packages, arrays
and modules. It does not provide guidance or
recommendations regarding prediction estimations
or extrapolations for lumen maintenance beyond the
limits of the lumen maintenances determined from
actual measurements.