Investigation of solutions to minimize flicker in LED lighting

Abstract

Therefore, the new knowledge contributed to the field by this dissertation study includes:

2) The tradeoffs between flicker index and power factor and power efficiency when designing a flicker reduction electronic circuit;

Since its first introduction to lighting industry in 2005, the alternating current (AC) light-emitting diode (LED) has experienced rapid development. Not needing an external driver is a distinct advantage AC LED has over direct current (DC) LED. The absence of an external driver could mean potentially higher system efficiency, fewer failure components, smaller system envelope, and lower system cost. However, one of the main drawbacks for AC LED is light flicker. According to past research studies, light flicker can cause negative health effects and also perception of light flicker is undesirable in lighting applications. A few of solutions, including electronic circuit and slow-decay phosphors, have been proposed to reduce AC LED light flicker. However, these solutions have come at the expense of lower power factor or low power efficiency in the case of electronic circuit. In the case of slow-decay phosphors, even though there are claims of reduced flicker, there aren't any studies that have shown quantified results. In a lighting system, a good solution should reduce light flicker while maintaining high values of other parameters such as power factor, power efficiency, system efficacy, color properties, and keep the system cost low.

In this dissertation, the author investigated and analyzed both approaches, electrical and optical, to understand the benefits and limitations of each method and quantified the tradeoffs with other important parameters of an LED system when reducing the flicker.

* Electrical study: The theoretical analysis and experimental validation of results showed that for the proposed flicker reduction circuit, the achievable lowest flicker index is about 0.4 while keeping high power performance (power factor > 0.9 and power efficiency > 90%). Even though the circuit reduced flicker index down to 0.4 it is still beyond the recommended value of 0.1 (by IESNA Handbook). Therefore, as an approach to further reducing the flicker index and achieving a good solution, the use of slow-decay phosphor in addition to the proposed electronic circuit was considered.

* Optical study: Once again, the theoretical analysis and experimental validation of results showed that it is possible to reduce flicker index to 0.1 while maintaining good quality white light using slow decay phosphors. The analysis further resulted in a set of recommendations for slow-decay phosphor properties, including, the acceptable range of values for the decay constant, peak wavelength, full-with-at-half-maximum, and phosphor efficiency.

With the knowledge gained in this study the industry can develop solutions to address the flicker issue faced by AC LED technology.

1) The maximum possible flicker reduction using an electronic circuit approach;

4) A mathematical model to simulate the resulting luminescence when a slow-decay phosphor is excited by a flickering source.

3) A set of recommendations for a slow-decay phosphor properties that can reduce flicker to an acceptable level while maintaining good quality white light;