LED照明控制.介绍

EE300: Lighting Control of LEDs, Part 1: Introduction to LED Control

Course Number: 000000003001

Educator: Kevin Willmorth

EDUCATION CREDIT

At the end of this course, participants will be able to complete an online exam, with a passing grade of 70+% to qualify for LEU (NCQLP) credit and

80+% for LU/HSW hours (AIA/CES). Upon a passing grade, you will be able to download a Certificate of Completion for each type of credits. For LC

certification maintenance (LEUs), credits are self-reported. For AIA /CES, Lighting Controls Association will report credit earned for this course to AIA CES.

NO ENDORSEMENT BY ACCREDITING ORGANIZATIONS

This course is registered with NCQLP and AIA CES for continuing professional education. As such, it does not include content that may be deemed

or construed to be an approval or endorsement by these organizations of any material of construction or any method or manner of handling, using,

distributing, or dealing in any material or product.

COPYRIGHT

This presentation is protected by US and International copyright laws. Reproduction, distribution, display and use of the presentation without written

permission of the Lighting Controls Association is prohibited.

DISCLAIMER

The information contained in this course has been obtained from sources believed to be reliable. Damages arising from errors, omissions or damages

as a result of the use or misuse of the data or information contained in this course are not the responsibility of the Lighting Controls Association,

National Electrical Manufacturers Association, ZING Communications, Inc., Lumenique, LLC or their employees or members. All information

contained in this course is published for professionals seeking information about the subjects contained therein. It is not the intent of this course

provide professional services such as design, engineering or consulting. If these services are sought, they should be rendered by properly trained,

registered, regulated and insured professionals

COURSE DESCRIPTION

LED technology delivers exceptional opportunities for lighting control application. However, due to

differences in how LEDs operate, controlling LED products differs from traditional light sources. This course provides a working understanding of

control methods for LED lighting products and how to integrate these methods into modern lighting design.

Part 1 offers an overview of LED drivers and power supplies and the impact of control functions on LED light output, efficacy, life, dimmer expectations and flicker behavior.

Part 2 shows how single-color white light LED products can be controlled within conventional wired control architectures.

Part 3 explores wireless controls advanced control physical layers and protocols applicable to modern solid-state and digital lighting applications.

Part 4 describes LED color how controls impact color performance of LED products, and methods used to control color and shade of white light.

Image courtesy of Lumenpulse

LEARNING OBJECTIVES

At the end of the course, participants will be able to:

·Understand how control effects such as dimming and switching affect LED sources

·Understand the basic function of LED drivers and the difference between constant-voltage and constant-current drivers

·Distinguish pulse-width and pulse-amplitude modulation and how they are used to adjust the luminous intensity of LED sources

·Identify when and why compatibility between controls and power supply components affects dimming performance

·Understand methods for attaining optimal performance of a controls scheme through careful product selection

COMPATIBILITY WITH LIGHTING CONTROL

Automatic lighting controls are common in new construction and frequently specified as an element of lighting upgrades. LED products are well suited

for operation with controls; LEDs are not negatively affected by frequent switching, and dimming has no negative impact on efficacy or service life.

LIGHT OUTPUT AND ENERGY

LEDs produce light output proportionally to energy input. An LED operating at 50% of its maximum current will produce roughly 50% of its initial light

output. Within the product’s design limit, higher current will generate higher light output.

DIMMING AND EFFICACY

Most LED devices rate initial lumens at a temperature of 25ºC; this is the temperature at which they are tested for optimum performance. However,

most LED luminaires operate LED devices at 35-80ºC. As temperature rises, light output and efficiency drop. Because dimming reduces temperature,

it increases efficacy. This means, as at the lowest settings, dimming of light levels is not proportional to actual dimmer power settings.

LED DRIVERS

LEDs are low-voltage direct-current (DC) light sources. Operation requires an electronic device that converts incoming AC to DC as the LED source

and circuit demand. These electronic components, known as “drivers” (because they drive current to the LEDs), also provide a control interface for

dimming and/or color control. Drivers and related components may be integral to the luminaire or located remotely.

Image courtesy of Lumenique

CONSTANT-VOLTAGE POWER SUPPLIES

Constant-voltage power supplies provide a fixed voltage required by the LED module (often 12 or 24VDC) within their output range. They provide

power directly to the LED source or to a current control driver that controls energy flow through the LEDs. This is a common approach where the LED

load is not known, such as track lighting and linear products of varying lengths.

When directly powering an LED circuit, resistors are typically used to regulate current flow. As these resistors produce no light but consume energy,

these power supplies are generally less efficient. For this reason, high-performance products utilize additional constant-current regulation in addition

to a constant-voltage power supply.

Image courtesy of Lumenique

CONSTANT-CURRENT POWER SUPPLIES

Constant-current drivers and power supplies regulate current while allowing voltage to fluctuate. They are generally more efficient and protect the

LEDs from overcurrent conditions regardless of operating temperatures or control setting. The power supply and driver may be separate components,

combined into single packages similar to a fluorescent ballast, or integrated into products themselves.

For dimming to be applied, the power supply and driver combination must be designed to include controls capability. If a product is not designed to be

dimmed, it cannot be connected to a dimmer, as changes to incoming power (line side) will upset operation of the driver and power supply, delivering unreliable results (or product failure)

Image courtesy of Lumenique

LINEAR VS. SQUARE LAW (LOG) DIMMING

Dimming controls utilize mathematical formulas to generate response behavior to dimming control settings. Linear formulas respond to control

movement in direct and straight line proportion—i.e., 10% control position = 10% light power setting.

Square law and log dimmers utilize formulas that attempt to create a dimming function that creates a variable relationship between control movement

and dimmer movement, creating a more natural feeling to the dimmer function.

DIMMING METHODS: VOLTAGE AND CURRENT REGULATION

The methods for controlling the brightness of LEDs include voltage regulation, current regulation, PWM and PAM modulation. The driver utilizes input

received from an external control and then processes that information to adjust output to the LEDs themselves to produce a desired light output.

Voltage regulation is the least useful, as LEDs have a limited tolerance to voltage changes, creating very limited dimming range with drop-OFF and

pop-ON effects. For this reason, products connected to constant-voltage power supplies are generally not dimmable.

DC current regulation is an effective method for controlling LEDs within a limited dimming range of 10-100% of full power. At lower current levels,

however, dimming performance can be inconsistent and unpredictable, and color shift may occur.

DIMMING METHODS: PWM CONTROL

An LED driver using pulse-width modulation (PWM) incorporates control circuits that alter the width of electrical pulses sent to the LED circuit. This

pulses the LEDs ON and OFF at a very high fixed frequency (28 kHz to 50 kHz, invisible to the naked eye). The advantage of this approach is that

current to the LEDs is maintained, which maintains the source at its peak efficacy at all settings. A wide pulse leaves the circuit ON longer, generating

more visible light; a shorter pulse leaves the circuit OFF longer, resulting in a reduction of light output.

PWM is also used as a control signal to a constant-current LED driver to produce variable current to the LEDs. PWM-controlled products are capable

of dimming to as little as 1% of full power (10% perceived brightness)

DIMMING METHODS: PAM CONTROL

In LED drivers that utilize pulse amplitude modulation (PAM), the current level is pulsed over time based on a variable or fixed frequency (10 kHz to

50 kHz). The change in current passing through the LED changes the level of light output, resulting in dimming. The maximum current is generally set

at the highest intended for the LEDs and modulated below that to reduce luminous intensity.

This blend of pulsed load and current regulation, combined with frequency variation, produces the highest level of precise control and is capable of

the lowest possible dim level setting (<10% perceived brightness). However, as the electronics involved are more costly, this approach is limited to

sensitive applications where high color fidelity is desired, such as color mixing. Typically, PAM is applied directly to the LED loads themselves and is

not used as a control signal.

AC OPERATION OF LED SOURCES

LED sources may be designed to operate directly on alternating current (AC) circuits either connected directly to line voltage or through simple low�

voltage transformers. Circuit connections that apply alternating current to produce the direct current LEDs require for operation results in a doubling

of incoming 50Hz or 60Hz AC sine wave frequency to an LED operating frequency of 100Hz or 120Hz, similar to magnetic fluorescent and HID

system output prior to electronic ballasts. Due to the limited voltage range tolerance of LEDs, however, flicker from these sources is aggravated by

any attempt to apply line-voltage dimming control. Further, the lack of through voltage from AC LED products will not support downstream

components such as photocells that require continuity for operation.

EXPECTATIONS: DIMMING PERFORMANCE ISSUES

Dimming of any light source presents challenges to system performance and integrity that require careful consideration. While flicker is one artifact of

poorly matched system components, other issues require consideration as well:

Dimmer control dead travel: when a range of control adjustment results in no change in brightness

Pop-ON: sudden run-up to an elevated brightness from zero;

Drop out: individual luminaires or groups of loads drop out as the control is moved to lower dim settings; and

inconsistent response to dimmer input.

These issues arise from controls interacting with drivers and power supplies in such a way as to deliver inconsistent interaction between a manual

dimmer control and the controlled load.

mage courtesy of Lumenique

COMPATIBILITY ISSUES

LED drivers and power supplies are electronic components designed to perform within a known set of operational conditions. Due to the large

number of variables between designs and manufacturers involved in providing the numerous components involved, compatibility issues may arise.

Interaction between incompatible electronic components, and failures in matching technologies properly, produces a range of undesirable effects.

FLICKER: INTERMITTENT FLUCTUATIONS

There are several forms of flicker. The simplest is noticeable as intermittent fluctuations in light output, often caused by variations in incoming line

voltage that are beyond what the power supply or driver can absorb. This is an intermittent issue that is mitigated through power line regulation.

Flicker may also be present in dimmed lighting products when the electronic components within dimmers and drivers or power supplies interact.

Effects include pulsing, fluttering, intermittent flickering at specific light levels, or as controls are moved through the dimming range. This type of

flicker can also be caused by an interaction between luminaires connected to neighboring controls on separate circuits. The only solution is to select

and apply compatible products and/or test combinations to ensure they do not cause the undesirable interaction.

FLICKER: STEADY STATE MODULATION

Flicker that is visible and constant is the biggest concern. How visible flicker appears to occupants

depends on frequency, modulation depth and duty cycle. Flicker is defined by a combination of flicker % and flicker factor.

Modulation of light sources at frequencies of less than 80Hz is well known to be visible to a majority of the population and have detrimental effects on

individuals susceptible to physiological response (e.g., epilepsy and migraine). Frequencies between 100Hz and 200Hz are considered tolerable by

most of the population when the flicker % is <10 and the flicker index is <0.04, but has been shown to negatively affect visual performance.

Frequencies over 2,000Hz are considered undetectable to the human visual system.

Source: IES Handbook, 8th and 9th Editions

FLICKER: A MATTER OF DESIGN AND PRODUCT QUALITY

Flicker may present in LED products of all configurations, particularly in products with low�

quality components and circuits that do not include the required filtering and AC/DC conversion.

This flicker is likely to be aggravated when the product is dimmed or controlled, with additional risk of control malfunction and reduced performance.

By design, however, high-frequency operation of LEDs (>2,000Hz) is considered invisible to occupants and is generally less susceptible to visible

flicker and control issues (in products rated as dimmable) than products that operate at line-voltage (100Hz or 120Hz) frequency.Source: M. Grather, LTL

DIMMER CONTROL QUALITY LEVELS

LED products dim according to the quality and design of the devices involved. Generally, low-quality luminaires and dimmers produce an inconsistent

“step dimming” effect and may offer dimming across a limited range. Further, low-quality dimmers designed to operate conventional lamps often

produce a greater rate of dimming relative to the control position, often resulting in the light level dropping to zero well before the control is in the

lowest setting position. Low-cost dimmers rarely deliver dimming to 20% of full light output. Additional electronic compensation is required to attain

10% or lower dimming range.

The highest-quality systems produce the smoothest dimming from settings as low as 1%. They not only dim to a lower level, but include programming

that dims the connected load using a log scale. This scale utilizes the entire control range, and results in lighting loads being dimmed at a rate that is

more closely matched to human perception of the dim rate. Further, these systems provide greater fidelity and full control range of motion.

GENERAL COMPATIBILITY OF CONTROLS

There are several different types of dimmers used in lighting. Not all are suitable for controlling LEDs. The following is a summary of the dimmer

types, and their likely compatibility

APPLICATION NOTES

There is currently no single standard establishing universal compatibility between LED products, drivers, power supplies and controls systems.

Before proceeding with the design of any control scheme involving LED products, carefully consider:

Not all LED products can be dimmed. If the driver and power supply are not designed to accommodate dimming, there are no controls available to

operate the products other than switches or relay contactors.

There are many proprietary LED products and systems that utilize unique controls systems or require adaptive integration modules to work with other

systems. Do not assume compatibility automatically exist between disparate manufacturers.

LED products may be incompatible with wallbox dimmers, photocells, sensor-based controls or electronic relays. These devices may include internal

resistive components that malfunction when connected to LED loads or circuits. Verify compatibility with the LED and control product manufacturers

prior to integrating them into a system.

Many LED products present a load that is below the minimum design capacity of standard dimmers, which will cause erratic dimmer response. This is

particularly problematic for retrofit applications using LED sources.

Application of low-wattage LED retrofit products on existing 12V transformers may not produce adequate load to support transformer electronic

function. Further, they may cause magnetic transformers to produce a higher output voltage.

Before considering any control of LED products—whether for switching, relay control, automatic sensor or dimming—verify that all selected

components are specifically compatible and supported by the manufacturers involved. When possible, test the intended component combinations to

ensure proper function.

YOU’RE FINISHED

This concludes The American Institute of Architects Continuing Education Systems Course EE300: Lighting Control of LEDs, Part 1: Introduction to

LED Control. You are now ready to take Part 2: Wired Control of LED Lighting.

Please take a moment to provide feedback about your experience with this course.

You may also take the Comprehension Test to test your learning and to qualify for LEU (NCQLP LC) and LU/HSW (AIA CES) credit. A 70+% passing

grade is required for LEU credit and 80+% for AIA CES credit. Upon passing the test, you may download a Certificate of Completion on the Courses

page. If you are an AIA member, please email your course completion certificate to LCA with your AIA number.