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The Race for LEDs


Digital LED Driver Technology Eliminates Harmful Flicker

March 24th 2012


With LEDs gaining traction in replacing incandescent bulbs, a downside of LED-based concepts is gaining visibility as well: There are concerns that the flicker associated with LED lamps might cause health problems - even epileptic seizures can be triggered by this phenomenon.

IEEE experiments suggest US-based LED driver company iWatt claims that its technology avoids these problems. Two factors cause LED lamps to flicker. One is the mains grid frequency that can introduce low frequency flicker to the LEDs which, in contrast to incandescent bulbs, do switch on and off at the rhythm of the grid frequency - much in contrast to conventional incandescent bulbs which are simply to inert to react on the grid frequency. The other factor that transforms LED lamps into nervously flickering lights are dimmers - available dimming circuits frequently are optimized for incandescent bulbs; they cannot cope with quickly reacting light sources such as LED lamps. Both factors added can cause significant flicker - and while it is a known fact that many LED lamps perform poorly when used with an electronic dimmer. However, this flicker is not just annoying but it can cause health problems.

Experiments of the Institute of Electrical and Electronic Engineers (IEEE) have demonstrated that the flicker in a commercially available LED lamp can into a frequency range that is known to cause photosensitive epileptic seizure, explains Scott Brown, Vice President of Marketing for iWatt, Inc, a privately held company producing driver ICs for LED lamps.

The reason for the poor performance of LEDs under dimming conditions is that LED lighting and LED dimming is not a simple linear problem - some lamps exhibit visible flicker at low dimmer settings or do not work with the dimmer at all. 

Brown claims that iWatt has created a technology that eliminates flicker in LED lighting. The company has developed a two-stage driver topology with patented digital control technology which eliminates flicker under all operating conditions, Brown promises. The algorithm implemented in iWatt's digital LED drivers maps the operating characteristics of dimmers and digitally filters the LED drive current, effectively eliminating voltage spikes that otherwise would cause flicker. The company has characterized a representative sample of dimmers available and implemented its algorithm accordingly, resulting in smooth dimming and ensuring the elimination of low frequency flicker. "Health concerns have to be taken seriously", Scott said. "But our LED driver technology provides a cost-effective solution to safely eliminate this problem". 

Christoph Hammerschmidt is the editor of EETimes Europe from where this article came from.

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