During this sessions, we will review the functions of components that make up an LED system, discover what characteristics of LED systems are required to achieve natural dimming performance, learn about what technologies are used to dim LEDs, define flicker, its causes and effects, learn how to mitigate the effects and understand how to reduce LED anomalies and assure desired performance.

1. Presented by: Mark Phillips, IES, CLEP
eldoLED / Acuity Brands

2.  Review the functions of components that make up an LED
system
 Discover what characteristics of LED systems are required
to achieve natural dimming performance
 Learn about what technologies are used to dim LEDs
 Define flicker, its causes and effects, learn how to mitigate
the effects and
 Understand how to reduce LED anomalies and assure
desired performance.

3. What the heck
is that?

4.  Flicker vs Continuous
 Shimmer vs Smoothness
 “Steppy” vs High Resolution
 Color Shift vs Maintaining Color
 Expected Light Level vs Full Range (0-100%)

5. Dimmer
input
LED Driver
response
LED
Light source
0-10V
DMX/RDM
DALI
Wireless
Forward Phase
Reverse Phase
Current Reduction (CCR)
Pulse Width Mod. (PWM)
Hybrid Method
Constant Voltage
Constant Current
The driver delivers the desired
performance in the luminaire
OR

6. Sending a signal to the driver
Not directly dimming the LED
0-10V
DMX/RDM
DALI
Wireless
Forward Phase
Reverse Phase

7.  Not all dimmers are created equal: some have linear responses, some have
logarithmic responses, and others exist
 To optimize the dimming experience, dimming curves in the drivers or in the
controls need to be configurable
X =

10. AC Input
Control
0-10V, DMX,
DALI...
+
Pulse Width
Modulation
(PWM)
Constant
Current
Reduction
(CCR)
Hybrid
The driver is similar to a fluorescent ballast but
will control an LED instead of a fluorescent tube

11.  Constant LED current,
varying LED on/off times
 Good dimming regulation at
deep dimming (same
current) levels
 Little color shift
X Potentially undesirable
flicker, depending on
frequency

12.  Varying LED current, LED
always on
 No flicker
 Higher LED efficacy at lower
dimming levels
X Poor dimming regulation at
deep dimming (low current)
levels

13. • Varying LED current, duty
cycle and frequency
 Best dimming regulation at deep
dimming levels
 High frequency operation)
 No flicker
 Dimming to dark
 No color shift when dimming Sec

14. Light level was not a concern of
incandescent dimming because it
dimmed to off
Square law dimming:
10% measured = 32% Perceived
5% measured = 22% Perceived
1% measured = 10% Perceived
0% measured = 0% Perceived
Shouldn’t this great technology we
have in LEDs meet, if not exceed, the
performance of older light sources?

15.  Digital drivers will change currents and with that brightness levels in digital steps
 The human eye is extremely sensitive for brightness changes at low light levels
 An LED has a very ‘unforgiving’ diode characteristic: it reacts immediately to any
change in drive currents - no ‘damping’
1 2 3
0.1%
0.103%
dimming setpoint
dimminglevel
To ensure a continuous perceived change of
brightness, the change in intensity from
setpoint 1 to setpoint 2 should be less than 3%

16.  Digital drivers will change currents and with that brightness levels in digital steps
 An LED has a very ‘unforgiving’ diode characteristic: it reacts immediately to any
change in drive currents - no ‘damping’
To ensure a continuous perceived change of brightness between minimum dimming
level and 100%, a minimum of 65,536 steps (16 bit resolution) is needed.

17.  Potential flicker-induced problems :
 Headaches, fatigue, blurred vision, eyestrain
 Neurological problems, including epileptic seizure and other biological effects
 ‘Unstable light output’ in video applications
Flicker is increasingly becoming a concern in the lighting industry.
Flicker, Why all the Buzz

18.  Incandescent
 HID
 Fluorescent
 And NOW LED

19.  The U.S. Department of Energy (DOE) defines
flicker as a “variation of light output over time”
 Repetitive change in magnitude over time, or
modulation, of the luminous flux of a light
source
 Every light source operating on an AC source
will have a modulated signal

20.  Visible Flicker: Flicker that is
consciously perceivable by a
human viewer.
 Invisible or Imperceptible
Flicker: Flicker that is not
consciously perceivable by a
human viewer
 Stroboscopic: indirectly
perceivable

21. IESNA has defined two
metrics for flicker:
 Percent flicker
 Flicker index
Source: IES Lighting Handbook, 10th Edition
A - B Percent Flicker = 100% XA+ B
Area 1 Flicker Index = Area 1 + Area 2
IES Metric Average Peak-to Peak
Amplitude
Shape Duty Cycle Frequency
Percent Flicker Yes Yes No No No
Flicker Index Yes Yes Yes Yes No

22.  3-70 Hz – Epileptic
Seizure risk
 70-165 Hz – Migraine
Inducement risk
 165-800 Hz - Visual
Impairment, stroboscopic
effects
Typical for dimmed LED today
Red=80% unacceptable
Yellow = 80% acceptable
White = imperceptible
Light Level 100%-10% 10%-5% 1% 0.1%
Percent Flicker <25% <100% 100% 100%
Min. Modulation
Frequency
>10 kHz >10kHz >1000Hz >1000Hz
Source: Assist Recommends…

23.  Requirements
1. Raise your hand
2. Shake your hand

25.  Demand Flicker % and Flicker Index
 Max Flicker Percentage – 40%
 Max Flicker Index - .15
 Frequency above 1 kHz
 Review Samples with your flicker
checker
 Get Active
 CALiPER
 IESNA and CIE are considering developing
standards
 IEEE creating recommended practices for evaluating
flicker risks
 Minimize Flicker – Ambient and Task
 Hospitals, Schools, Clinics, Offices, Classroom and
Daycare

26.  California Energy Commission (CEC)
 Voluntary California Quality Light-Emitting Diode (LED) Lamp
Specification, December 2012
 Title 20
 Zhaga
 Book 1
 EPA EnergyStar
 Lamps and Luminaire specificaitons

27.  A forward-looking standard developed to reduce
anomalies with LEDs and phase cut dimmers
 It contain design specs for LEDs, drivers, engines,
controls and test guidelines for help determining
compatibility
 Ex. An SLL-7A compliant lamp and dimmer must be used
together, which will yield a compatible solution
 Released in mid-2013 and created for new products,
not existing equipment

28.  Understand the application requirements and set an expectation for the customer,
natural dimming is possible if correct technology is implemented
 Know what components will make up your system (control, driver, LED)
 Consider the driver and its capabilities, know which type the fixture manufacturer is using
 Ask about its flicker percentage or index, know what perceived light level it can dim down
to and what the dimming resolution is
 Ask the luminaire manufacturer for a driver that meets your requirements

29. Thank you for your attention!!!
Questions?