mobile | classic
Dataweek Electronics & Communications Technology Magazine

Follow us on:
Follow us on Facebook Share via Twitter Share via LinkedIn


Electronics Buyers' Guide

Electronics Manufacturing & Production Handbook 2019


LED flicker, and how to prevent it
28 August 2019, Opto-Electronics

With the growing popularity of LED lighting, especially now that very cheap LED luminaires are coming to the market, flicker is becoming more of a problem.

Flicker, a repetitive switching on and off of the light source, isn’t a problem for incandescent bulbs because if the power supply to the bulb drops momentarily, the element doesn’t lose sufficient heat for the light output to diminish. With LEDs, however, once the supply current drops below a certain level, no matter how briefly, the light will turn off (an LED takes around 300 µs to turn off). In fact, pulse width modulation (PWM) control schemes used in dimming use this effect at high frequency to dim the light output. It is lower frequencies, even those above 80 Hz that aren’t visible to the naked eye, that cause problems.

Flicker present in LED lighting, even if not visibly perceptible, can have serious consequences for people’s health, especially if they are exposed for long periods of time. At one end of the scale, it can be annoying and distracting, and even slow text reading speed by 30%. It can also cause eyestrain, blurred vision and dizziness. The most serious problems flicker can cause include migraines and even triggering epileptic seizures (if in the range of 3 to 70 Hz).

LED lighting flicker can also cause technical problems, for example, if used in sports stadium lighting, invisible flicker can be very visible when camera footage is slowed down for replays. More significant levels of flicker can also cause havoc with video footage played back at normal speed, appearing as dark lines across the picture.

The causes of flicker include cheap and simple LED drivers that use rectified mains to power the light source. While electrolytic capacitors are used to reduce ripple in the output current, they are expensive and bulky components, which are often the cause of failure of luminaires because of their relatively short lifetimes. For these reasons, manufacturers often skimp on capacitor specifications when budget is tight.

The frequency of rectified mains would be 100 Hz in Europe or South Africa, or 120 Hz in the US, which is right in the problem area. Poor-quality LED dimmer circuits whose PWM frequencies are below 200 Hz are another common culprit, along with electromagnetic interference from external noise sources.

Flicker may be measured in a number of ways. The most common are flicker percentage and flicker index. Percentage flicker is a measure of the depth of modulation of flicker, simply comparing the maximum signal level to the minimum. Lower percentage flicker means less substantial light flicker is present.

Figure 1.A theoretical LED driver output signal used to demonstrate the percent flicker and flicker index.
Figure 1.A theoretical LED driver output signal used to demonstrate the percent flicker and flicker index.

The more informative metric, flicker index, accounts for the different possible duty cycles of the drive signal, comparing the duration of high and low light levels with the average intensity. Lights can have similar flicker percentage while having very different flicker index (i.e., very differently shaped drive signals).

Referring to Figure 1, the formulae defining these two metrics are:

Percent flicker = 100% x (max - min) / (max + min)

Flicker index = area above mean / total area = Area 1 / (Area 1 + Area 2)

There is a relatively new industry standard that regulates the amount of acceptable flicker in LED lighting, IEEE SA-1789-2015. This standard provides guidance to help manufacturers design or select suitable LED drivers in order to minimise health and productivity effects due to flicker (in contrast to previous versions of the standard which focused on visible flicker).

This standard sets relatively strict levels of acceptable flicker in lighting – this is 8% flicker for countries where the mains frequency is 50 Hz, and 10% for countries where it’s 60 Hz. It was quite controversial when it was introduced, as it implied that many LED lights on the market actually had negative effects on health. Even today, there are actually not that many LED drivers on the market that can meet this strict standard.

Figure 2. Mean well IDLC-45 45 W LED driver.
Figure 2. Mean well IDLC-45 45 W LED driver.

Meeting this IEEE standard for flicker means choosing a driver circuit carefully, and probably paying a bit more for it. For good flicker performance, it’s necessary to avoid simple, low-cost, single-stage circuits that use rectified mains with insufficient capacitor smoothing, as these often have high ripple currents. 30% flicker for this type of circuit is absolutely not uncommon.

Drivers that have a constant-current mode are recommended for low-flicker applications. For example, the IDLC-45 series from Mean Well is a range of 45 W LED drivers with a constant-current mode output for LED panel lighting, flood lighting and indoor lighting. The IDLC-45 series features ripple current below 5%. Fulham also has the 30 W L05031 in its Lumo series, which is a high-performance driver that offers output ripple current at less than 1%.

Figure 3. Fulham Lumo L05031 W high-performance LED driver.
Figure 3. Fulham Lumo L05031 W high-performance LED driver.

For those designing a lighting application that requires minimal flicker and needing advice on driver selection, Avnet’s team of technical specialists is on hand to assist.

For more information contact Avnet South Africa, +27 11 319 8600,

Supplied By: Avnet South Africa
Tel: +27 11 319 8600
Fax: +27 11 319 8650
  Share on Facebook Share via Twitter Share via LinkedIn    

Further reading:

  • Qi-compliant wireless charging coils
    28 August 2019, Avnet South Africa, Passive Components
    Vishay has expanded its offering of Qi-compliant wireless charging transmitter and receiver coils with the introduction of 14 new products in industry-standard shield sizes. Consisting of eight single-coil ...
  • Digital fibre-optic sensor
    28 August 2019, Vepac Electronics, Opto-Electronics
    The DFS digital fibre-optic sensor series from Tri-Tronics is designed to provide reliable detection using plastic fibre-optic light guides. The slim-line housing with protective lid will fit in a variety ...
  • All-in-one light pipe system
    28 August 2019, Vepac Electronics, Opto-Electronics
    Bivar’s Zero Light Bleed adaptor technology, with built-in surface-mount LED, channels light directly to the lens, eliminating disruptive light bleed. The all-in-one adaptor system is built with optimum ...
  • 3 Watt DC-DC converters
    28 August 2019, Avnet South Africa, Power Electronics / Power Management
    Aimtec has introduced three new series of switching regulators – the AMSRB1-78JZ, AMSRL1-78JZ and AMSRL-78JZ – all meeting the EN62368 standard and suitable for IoT (Internet of Things) applications. The ...
  • Buck converter with low quiescent current
    31 July 2019, Avnet South Africa, Power Electronics / Power Management
    Texas Instruments introduced an ultra-low-power switching regulator with what it claims is the industry’s lowest operating quiescent current (IQ) at 60 nA. The TPS62840 synchronous step-down converter ...
  • MCUs with industrial communication interfaces
    31 July 2019, Avnet South Africa, DSP, Micros & Memory
    Texas Instruments introduced new communications capabilities on its C2000 microcontrollers (MCUs). C2000 F2838x devices enable designers to use a single chip to implement connectivity, including EtherCAT, ...
  • High-intensity colour LEDs
    31 July 2019, Würth Elektronik eiSos, Opto-Electronics
    Würth Elektronik has expanded its LED portfolio with a particularly compact model family. The WL-SMCC series of SMT chip LEDs, available in 0402 and 0603 packages, is characterised by a full-surface lens ...
  • A quick guide to multi-standard mesh networking
    31 July 2019, Avnet South Africa, Telecoms, Datacoms, Wireless, IoT
    Recent advances in wireless technology have enabled the use of mesh network topologies in home and building control applications. Low-cost IoT technology is driving the launch of devices such as smart ...
  • RGB LEDs for decorative lighting
    26 June 2019, Würth Elektronik eiSos, Opto-Electronics
    Würth Elektronik’s new WL-SFTW and WL-SFTD series of RGB LEDs are targeted at accent and decorative lighting, optical displays as well as industrial applications. Thanks to their PLCC contacting design, ...
  • eSPI-to-LPC bridge
    26 June 2019, Avnet South Africa, Computer/Embedded Technology
    Microchip Technology’s new ECE1200 bridge allows developers to implement the eSPI standard in boards with legacy LPC connectors and peripherals. Product longevity is critical in industrial computing ...
  • Designing certified power solutions for LED lighting
    26 June 2019, Avnet South Africa, Power Electronics / Power Management
    LED lighting has become the product of choice in all types of environments, from domestic to industrial through to specialist areas such as stage lighting. The combination of efficiency in terms of lumens ...
  • Automotive smart hub ICs
    26 June 2019, Avnet South Africa, Telecoms, Datacoms, Wireless, IoT
    Microchip Technology has added new single-port USB smart hub ICs to its family of USB automotive products. The USB4912 and the USB4712 can be used to add a single port under the radio, in the centre console ...

Technews Publishing (Pty) Ltd
1st Floor, Stabilitas House
265 Kent Ave, Randburg, 2194
South Africa
Publications by Technews
Dataweek Electronics & Communications Technology
Electronics Buyers’ Guide (EBG)

Hi-Tech Security Solutions
Hi-Tech Security Business Directory

Motion Control in Southern Africa
Motion Control Buyers’ Guide (MCBG)

South African Instrumentation & Control
South African Instrumentation & Control Buyers’ Guide (IBG)
Terms & conditions of use, including privacy policy
PAIA Manual


    Classic | Mobile

Copyright © Technews Publishing (Pty) Ltd. All rights reserved.