The IEEE Standards Working Group, IEEE PAR1789 “Recommending practices for modulating current in High Brightness LEDs for mitigating health risks to viewers” has been formed to advise the lighting industry, ANSI/NEMA, IEC, EnergyStar and other standards groups about the emerging concern of flicker in LED lighting. This paper introduces power electronic designers for LED lighting to health concerns relating to flicker, demonstrates that existing technologies in LED lighting sometimes provide flicker at frequencies that may induce biological human response, and discusses a few methods to consider when trying to mitigate unintentional biological effects of LED lighting. The paper represents on-going work in IEEE PAR1789 that is vital to designing safe LED lamp drivers.

LED lighting flicker and potential health concerns: IEEE standard PAR1789 update

Domestic induction cookers operation is based on a resonant inverter which supplies medium-frequency currents (20-100 kHz) to an inductor, which heats up the pan. The variable load that is inherent to this application requires the use of a reliable and load-adaptive control algorithm. In addition, a wide output power range is required to get a satisfactory user performance. In this paper, a control algorithm to cover the variety of loads and the output power range is proposed. The main design criteria are efficiency, power balance, acoustic noise, flicker emissions, and user performance. As a result of the analysis, frequency limit and power level limit algorithms are proposed based on square wave and pulse density modulations. These have been implemented in a field-programmable gate array, including output power feedback and mains-voltage zero-cross-detection circuitry. An experimental verification has been performed using a commercial induction heating inverter. This provides a convenient experimental test bench to analyze the viability of the proposed algorithm.

Load-Adaptive Control Algorithm of Half-Bridge Series Resonant Inverter for Domestic Induction Heating

Visible Light Communication (VLC) is an emerging technology in which Light Emitting Diodes (LEDs) transport information wirelessly, using the visible light spectrum. While most of the research on VLC has focused on wideband white LEDs used in ambient illumination, narrowband and colored LEDs have received little attention. Short-range free-space optical communication based on narrowband LEDs as visible light transmitters and receivers enable a variety of applications, a scenario we refer as LED-to-LED communication. In this paper, we introduce the communication and networking protocols of LED-to-LED communication. Our work addresses fundamental challenges such as efficient collision detection medium access protocol and elimination of light flicker. We build a prototype and demonstrate bi-directional data exchange in a network of up to four LEDs. We further study the trade-offs in the system design and measure the achievable bit-rate and transmission distances.

/pdf/low-complexity-visible-light-networking-with-led-to-led-129uk9b64s.pdf

Low-complexity Visible Light Networking with LED-to-LED communication

Flickers and interharmonics have an inherent relationship. The magnitude of a voltage can fluctuate if it contains interharmonics. This paper proposes a limit for interharmonics by utilizing the published limits on voltage flicker. The limit is presented as an interharmonic-magnitude versus interharmonic-frequency curve and is called interharmonic-flicker curve. The interharmonic-flicker curves based on the rms and peak magnitude fluctuations and on the IEC flickermeter are derived. A systematic method to derive limits for interharmonics from the flicker limits is presented. The paper also reveals that the IEC flickermeter needs improvement when dealing with interharmonic-caused flickers. Potential applications of the proposed interharmonic-flicker curves include the designing and evaluation of mitigation measures to reduce the flicker impact of interharmonic producing sources.

Interharmonic-flicker curves

Nowadays, more and more lamp types are being used. Since different lamp types have different working principles, they also have different flicker responses. This paper shows the measurement results of different flicker responses for various types of lamps. These results prove that the UIE/IEC flickermeter, which has been used widely around the world for many years, cannot be used to advise on the flicker level of all lamp types. This is because of the fact that this flickermeter is based on a 230 V, 60 W or 120 V, 60 W incandescent lamp and can be used as reference only for this type of lamp or as reference to the standard. The UIE/IEC (International Union for Electricity Applications/International Electrotechnical Committee) flickermeter and the existing standards are therefore insufficient for other lamp types. This paper describes a proposal to improve the UIE/IEC flickermeter.

/pdf/flicker-responses-of-different-lamp-types-15fddt9lu7.pdf

Flicker responses of different lamp types

This paper is intended to provide an overview of the IEC flicker measurement and assessment procedures. The IEC procedures are correlated with existing IEEE flicker standards to show the benefits of the IEC methodology. Application issues, such as customer impact assessment, are also discussed. Three case studies, two field tests, and one EMTP analysis are provided to show the correlation of IEC flickermeter output values with documented customer complaints. The case studies also provide areas where modifications to the IEC flicker standards may be necessary when developing a new IEEE flicker standard.

L.E. Conrad

Papers

Voltage and lamp flicker issues: should the IEEE adopt the IEC approach?