In this Issue!
Controlling LEDs
• LED Dimming
Technologies
• LED Dimming
Performance
• DMX: The Rules of the
Road
• Further Reading and
Resources
Controlling LEDs
Dimming LEDs can increase worker productivity, enhance the experience of
diners in a hospitality setting, and save energy, but you have to correctly
combine controls, drivers, and LED sources.
The growing popularity of LED light sources is rooted in energy savings, long life,
and new fixture options that enable them to be used in almost any application. A
25W LED lamp can replace the light output of a 100W incandescent lamp, deliver
a useful lifetime averaging 50,000 hours (compared to 10,000-20,000 hours for
fluorescent lamps and 3000 hours for halogen lamps), and offer very good color
rendering. LED lamps also emit very little infrared radiation, and they contain no
mercury.
These advantages ensure a strong future for LEDs, but there are challenges
associated with using LEDs to meet customer expectations. Compatibility
between LED lamps, drivers, and controls can be confusing, and if they are
specified improperly, performance will suffer. The best strategy for selecting an
LED product is a holistic approach that takes into consideration a variety of
factors including the application type, required dimming performance, and
control preferences.
(Excerpt from an article published in the Spring 2013 issue of Illumination In Focus Magazine.)
JTH Lighting Alliance
6885 146th Street West
Apple Valley, MN 55124
JTH Lighting Iowa
1000 Walnut Street,
Suite 102
Des Moines, IA 50309
888-746-4584
controls@jthlighting.com
www.jthlighting.com
LED Dimming Technologies
There are two main approaches to dimming LED sources. The first is coincident AC
power and controls signal, that is the AC power’s sine wave is modified to achieve
dimming. The second approach is separate AC power and control signal, where the AC
power remains unchanged and dimming is controlled by the LED driver.
Coincident AC Power and Control Signal
• Forward Phase Dimming - AKA "Triac Dimming", "SCR Dimming“ - Forward Phase
Forward Phase
Dimming
Dimming control is the most common form of dimming. It uses a silicon device,
usually an SCR or a Triac, to turn the mains waveform on part way through its cycle.
They are not designed to control LED and using them to do so may result in
inconsistent or limited performance.
• Reverse Phase Dimming – AKA “ELV” - Reverse Phase Dimming takes the opposite
approach to Forward Phase Dimming and switches the sinewave off part way
through the cycle. ELV Dimmers control electronic low voltage transformers (ELVs)
and dimmable LED power supplies such as those found in ELV track lighting, under
cabinet lighting and LED strips.
Reverse Phase
Dimming
• Sine Wave Dimming - Sinewave dimming acts in a similar way to running a load via
a variable transformer; a true variable voltage is supplied to the load. Sinewave
dimming has many benefits including very low or silent lamp noise and lower power
consumption, but is more expensive to install initially. This type of dimming is rare.
Separate AC Power and Control Signal
• 0-10V - An analog lighting control protocol. Basically, a 0-10V control applies a
voltage between 0 and 10 volts DC to produce a varying intensity level.
•
DALI - (Digitally Addressable Lighting Interface) is a specific type of control that uses
digital signals to send intensity information to the LED drivers. The digital command
set is defined in Annex E of IEC60929. There are two ways to implement DALI
control. One is by sending individual intensity values to addressable devices on the
loop. The second method is to broadcast a single intensity value to all devices on the
DALI loop.
•
DMX512 - A standard that is defined by USITT-DMX512-A. It describes a method of
digital data transmission between controllers and lighting equipment and
accessories. It is widely used in theatrical and architectural lighting applications.
DMX512 is able to provide an extensive array of control options for this type of LED
control primarily due to its ease of programming and ability to address large
numbers of devices at the same time.
• PWM - An excellent method of dimming LEDs is to use Pulse Width Modulation
(PWM). With PWM strings of LEDs can all be driven with the recommended forward
current, with the dimming achieved by turning the LEDs on and off at high frequency
- so fast the human eye cannot see the strobing effect. The longer the “on” periods
are relative to the “off” periods, the brighter the LEDs will appear to the observer.
Sine Wave
Dimming
LED Dimming Performance
Not all LEDs are created equal. A product that dims to 20% measured light (45% perceived light as documented in the
IESNA handbook) wouldn't make sense in a media room, but may be an appropriate energy-saving solution for an
office. If an LED fixture or lamp specification sheet does not state the dimming range, you should contact the
manufacturer for that important piece of information. The dimming range of a product, either a lamp or a fixture, is
based solely on the driver. Choosing the right dimming control will allow you to reduce flicker and may affect your
ability to achieve the desired dimming range, but the dimmability, low-end light level, and performance of the product
are determined by the driver. A good driver should account for these performance factors and still provide flicker-free,
smooth, and continuous dimming of the LED source. The driver determines the achievable dimming range and the best
possible performance of the lamp or fixture. The control determines whether or not the best possible performance is
realized in the application.
DMX: The Rules of the Road.
As the standard control protocol for color changing LED fixture, DMX data runs are becoming common in many
installations. The current standard known as "E1.11 – 2008 (R2013) USITT DMX512-A", or just "DMX512-A“. Although
DMX is a flexible protocol for the operation of intelligent fixtures, there are hard rules of how the data can be
distributed.
DMX512 requires cabling between devices to be done in a point-to-point daisy-chain fashion. A star layout is not
permitted (no ‘Y’s, stubs, or branches). If the physical requirements of a system do not allow for a daisy-chain
installation, then the use of DMX512 splitter (sometimes referred to as repeaters or amplifiers) is required.
The cable should be suitable for EIA-485 (RS-485) use, with one or more low capacitance twisted pairs, with overall
braid and foil shielding. Typically Belden 9729 or equal advised. Ethernet cable may also be used but is subject to some
care and limitations in the Installation.
Typically DMX lines can have up to 32 devices down its length. There are some devices that can allow for more on a run
but these are special cases and need to planned carefully. If more devices are needed on a run, a DMX repeater is
required. One thousand (1000) total feet is the advised run limit for each cable run.
All DMX runs require a terminator. This prevents signal reflection that could cause unpredictable behavior. Some
devices are fitted with a switch to select an internal terminator. This switch may be labelled ‘end-of-line’ or ‘last-rack’.
It should only be switched on in the last device on the line.
Further Reading and Resources
Last Tidbit
Understand Compatibility, Performance, and Dimming Issues in LED
Lighting (Spring 2013 Illumination In Focus magazine)
http://www.ledsmagazine.com/articles/iif/print/volume-2/issue6/features/understand-compatibility-performance-and-dimmingissues-in-led-lighting-magazine.html
When specifying a particular
LED driver, fluorescent ballast,
or electronic low voltage (ELV)
transformer for use with a
Dimming System, it is best to
verify that the device is
compatible before installation.
LED Dimming: What you need to know (USDOE) http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/dimmin
g_webcast_12-10-2012.pdf
The LED Dimming Dilemma (March 2013 EC&M) http://ecmweb.com/lighting-amp-control/led-dimming-dilemma
DMX standard and User Guide
PLASA Technical Standard Program - Published Documents
JTH Lighting’s control
manufacturers not only
maintain lists of compatible
lamps and fixtures but also
offer free testing.
Verbatim Lamp/Dimmer Compatibility
http://www.verbatimlighting.com/dimmer_support
Additionally JTH can provide
performance tests in house or
at a location of your choice.
SORAA Lamp/Dimmer Compatibility
http://www.soraa.com/wws/dimmers
Contact your JTH sales agent
for more information.
Jerry Kraft, ETCP TR/EE, USITT
Rigging & Project Specialist
jerryk@jthlighting.com
Todd Reemtsma, IES, LC, USITT
Controls Group Sales
toddr@jthlighting.com
Joe Setten
Controls Inside Sales
joes@jthlighting.com
JTH Controls Group
controls@jthlighting.com
Debbie Rosko
Controls Project Manager
debbier@jthlighting.com
JTH Lighting Alliance
6885 146th Street West
Apple Valley, MN 55124
JTH Lighting Iowa
100 Walnut Street, Suite 102
Des Moines, IA 50309
888-746-4584 –Toll Free
www.JTHLighting.com