Presented by: Mark Phillips, IES, CLEP

eldoLED / Acuity Brands

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.

What the heck is that?

Flicker vs Continuous

Shimmer vs Smoothness

“Steppy” vs High Resolution

Color Shift vs Maintaining Color

Expected Light Level vs Full Range (0-100%)

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

Sending a signal to the driver

Not directly dimming the LED

0-10V

DMX/RDM

DALI

Wireless

Forward Phase

Reverse Phase

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 =

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

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

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

• 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

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?

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 setpointdim

min

g l

evel To ensure a continuous perceived change of

brightness, the change in intensity from setpoint 1 to setpoint 2 should be less than 3%

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.

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

Incandescent

HID

Fluorescent

And NOW LED

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

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

IESNA has defined two

metrics for flicker: Percent flicker

Flicker index

Source: IES Lighting Handbook, 10th Edition

A - B Percent Flicker = 100% X A+ 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

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…

Requirements

1. Raise your hand

2. Shake your hand

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

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

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

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

Thank you for your attention!!!

Questions?