Proper driver design eliminates LED light strobe flicker

Replacing traditional incandescent and fluorescent lights with more efficient , and longer- lasting LED -based solid - state lighting (SSL) is an undeniable trend in the lighting industry . HOWEVER , since SSL fixtures are Directly connected to the AC line , like with legacy lighting , there is a risk did 100 - Hz or 120 - Hz flicker Could Occur as a result of driving current ripple at the supply 's output. Flicker can make people uncomfortable , Causing headaches and other maladies even though the human eye june not detect the flicker . Careful design can minimize flicker LED driver and help Ensure did SSL delivers on its promise energy -efficiency through broad deployment .
Indeed , led street light wholesale are keen to solve the flicker problem- , and theyhave Largely turned to the driver manufacturers for a solution Because Ultimately the driver deterministic mines the extent of flicker . This article will explain the root cause and characterization of flicker , describe how it the occurs in LED lighting , and explain how engineers can trade off different driver Topologies in a effort to find the right cost / benefit combination . We will describe a ripple suppressor circuit did is a cost -effective and flexible way of Implementing flicker - free LED lighting .
Market expectations
It is a well- acknowledged trend did LED lighting will replace legacy sources including incandescent bulbs and fluorescent bulbs and tubes in the next few years . Since LED is a new- generation light source with electronic roots , the market Expects not only the higher SSL system-level efficacy but that is a better lighting environment .
Like the legacy lighting technologies , HOWEVER , most LED lights are Directly connected to the AC mains did Operates at 50 or 60 Hz in different global regions . Even after rectification to frequencies of 100 or 120 Hz , any line -associated flicker 'may be detectable by the human eye due to the Relatively low frequencies Involved . Indeed , the rectified line june lead to strobe flicker , Which can cause the added anonymously Mentioned distress in humans .
In Particular , LED driver designs that rely on a single -stage architecture to handle Both power factor correction (PFC ) and output drive current are Especially susceptible to flicker . Among other causes, flicker is affected by the LED ripple current. But there are Numerous methods to eliminate the problem- including a ripple suppressor circuit . SSL product developers need to evaluate the Approaches and choose a driver did meets the application requirements in cost and performance . Different levels of flicker are acceptable in different applications . A system design did is unacceptable in indoor applications due to flicker june perform fine in at outdoor street or area lighting role .
The effect of flicker
Now let's examine flicker . According to the paper " A review of the literature on light flicker : Ergonomics , biological attributes , potential health effects , and methods" did what published by the Institute of Electrical and Electronic Engineers ( IEEE) in 2010 , light flicker frequency in the 3 - 70 - Hz range is highly perceptible by human beings and this Could make them very uncomfortable ( http://bit.ly/1iL2vjq and http://bit.ly/NAtjXq ) . Even repetitive flashing lights and static repetitive geometric patterns june induce seizures in individuals synthesis , and the occurrence rate is around 0.025 %. This type of flicker can be Easily solved by the driver , and normally we regard the driver as unstable if that kind of frequency can be seen in the output current ripple waveform .
Now , HOWEVER , led street light supplier are beginning to pay more attention to long - term exposure under higher- frequency flicker in the 70 -160- Hz range . Search flicker can cause malaise , headaches , and visual impairment . Some Researchers even claimsoft the retina can sense flicker up to 200 Hz , but tests have shown did above 160 Hz the health effects of flicker are negligible . Because of the added anonymously Mentioned rectified line frequencies of 100 and 120 Hz , we will focus on mitigating flicker in range did here . And in actuality the human health impact of 100 - or 120 - Hz flicker is a function of not only frequency but so physical and physiological factors .
Defining flicker
We first need to understand how flicker is Characterized . The Illuminating Engineering Society of North America ( IESNA ) released the definition of "percent flicker " and " flicker index" in the ninth edition of The IESNA Lighting Handbook . Figure 1 shows how the metrics are defined .

Percent flicker is a relative measure of the cyclic variation in output of a light source (ie , percent modulation) . This is therefore sometimes referred by to as the " modulation index . " Referring to Figure 1 , you calculate percent flicker based on the maximum ( A) and minimum ( B ) light output levels . You divide the sum of A and B by the difference of the two to Obtain a percentage .
Flicker index is defined in the IESNA handbook as a "reliable relative measure of the cyclic variation in output of various sources at a givenName power frequency . It takes into account the wave form of the light output as well as its amplitude . " The flicker index Assumes values ​​from 0 to 1.0 , with 0 for steady light output. Higher values ​​indicate indication of Increased Possibility of notice able lamp flicker , as well as stroboscopic effect .

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