LED Flickering: A Devil hides under the Light

Steve Law

January 2015

Introduction

Invented by American Inventor Nick Holonyak Jr in 1962, Light Emitted Diode (LED), as commonly believed, is a completely new energy saving lighting technology with series of advantages, for example, a much lower energy consumption and a much longer lifespan. However, there are still shortcomings within LED products, while flickering is the most common one (Chen L and Zhan WX, 2014) . Over the last few years, a large number of LED luminaires have been found to exhibit serious visual flickers. Especially for retrofit MR16 or GLS lamps, which can have various types of flickers, due to the poor compatibility of commercial and domestic dimmers. Graph 1 and 2 had illustrated the speed camera test results of two LEDs. It can be seen that the experiment downlight of Graph 1 had displayed a strong 100Hz flicker, which may be from an inadequate DC converter. In comparison, the luminaire of Graph 2 had exhibited no visible flicker. (Hammarb ck, 2013)

Typically, flickers of LED lights are in a high frequency flickering (>1000Hz). Although it is normally invisible ripple for most people, it can still trigger a series of ocular illness. That is why I call LED flicking a devil that hides under the bright light.

IMG_3503 IMG_3502
Graph 1 Speed camera photo test for flickering LED downlight Graph 2 Speed camera test for non-flickering LED downlight

Problems

According to the research from Nantong University, China (2011), under flickering lights, pupils in human eyes needs to adjust frequently for the visualisation on the macula, this will likely cause eyestrain and myopia(Yu et.al., 2011).  Even worse, researchers from the State of Ohio University, USA claims that long term expose in low frequency flicker lights can cause severe vision-threatening diseases such as detachments, choroid atrophy, cataracts and glaucoma (Walline et. al., 2011) .Besides, if the flickering is in a frequency as high as several kHz, human eyes cannot be able to adjust fast enough to adapt the variation of irradiance. Thus, the excessing amount of light spectrum from the Led light will damage the retina, and causing photomechanical damage (Chen L and Zhan WX, 2014).

On the other hand, it is indicated by some other researches that the impact of flickering can be varied, as some people are naturally more sensitive to ripple of lights. Even for the same person, the flicker threshold and the critical flicker fusion can also varied in accordance of time of day, mood, stress, hormone levels, etc. (Wilkins,2010). Nonetheless, against all the negative effects above, there is no doubt that LED flickering is not acceptable.

Solution

Frankly, there is no single solution for LED flickering. Although IEEE PAR1789 had initiated a series of measures for safe flicker levels from LED lights. Unfortunately, these works are still in progress, and some time will be taken for it to formalise into specific standards, and additional time is also needed for these new technologies to be commercialized. Thus, to tame this devil, there is still a long way to go (Hammarb ck, 2013).

However, as a consumer, it is not necessary to get headache by considering all of the technical issues, as there a simple measure to avoid LED flickering, which is to find out the flickering index of a certain LED luminaire. This data can be found on the website of LED Benchmark®, an independent testing laboratory for LEDs. Graph 3-1 and 3-2 had shown the result of flickering test for two different LED products. It is obvious that luminaire A has a lower flickering than luminaire B, as it is indicated by to the much lower value of flickering index and percentage.

3-1 3-2
Graph 3-1 flickering test result of Luminaire A Graph 3-2 flickering test result of Luminaire B

(Source: LED Benchmark)

Summary

Even though we are not yet able to resolve LED flickering, we can still easily get away from this devil by paying more attention when choosing an LED product. So, next time when you are looking for an LED light, please keep an eye on its flicking data, instead of only looking at the prices.

Reference:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3949479/

Hammarb ck. P (2013), LEDs and Return of the Flickering, Lighting Magazine (October/November 2013), page 36-38

Yu Y, Chen H, Tuo J, Zhu Y. Effects of flickering light on refraction and changes in eye axial length of C57BL/6 mice. Ophthalmic Res. 2011;46(2):80–87

Walline JJ, Lindsley K, Vedula SS, Cotter SA, Mutti DO, Twelker JD. Interventions to slow progression of myopia in children. Cochrane Database Syst Rev. 2011;7(12):CD004916

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3949479/

Wilkins,A (2010) LED Lighting Flicker and Potential Health Concerns:IEEE Standerd PAR1789 Update. Energy Conversion Congress and Exposition (ECCE),2010 IEEE, pp 171-176

Hammarb ck. P (2013), LEDs and Return of the Flickering, Lighting Magazine (October/November 2013), page 39