On the color stability of phosphor-converted white LEDs under DC, PWM, and bilevel drive

Ka Hong Loo, Y. M. Lai, Siew Chong Tan, Chi Kong Tse

Research output: Journal article publicationJournal articleAcademic researchpeer-review

69 Citations (Scopus)


Most commercial white LEDs are made from nitride-based blue LEDs coated with yttrium aluminium garnet phosphor, which produce spectra that shift in opposite directions under the influences of drive current and junction temperature changes. This property gives rise to different emitted spectra, hence chromaticity properties, when the LED is driven/dimmed by different current waveforms. By using a commercial white LED sample, LUXEON K2, the effects of drive current and junction temperature on the changes of chromaticity coordinates are studied experimentally. The impact of dc, pulse width modulation (PWM), and bilevel current waveform is discussed through a graphical analysis, followed by experimental verification. It is proven that dc offers the best color stability over dimming due to the counteracting influences of drive current and junction temperature variations, whereas an LED constantly suffers from noneliminable chromaticity changes when driven by the PWM. Theoretical explanations are given to justify these cases, and it is found that, for the case of dc drive, an ideal heat sinks thermal resistance can be selected based on a simple equation to minimize the overall chromaticity change over dimming. This paper provides an in-depth discussion on the relations between the chromaticity properties of phosphor-converted (pc) white LEDs and the driving/dimming methods used.
Original languageEnglish
Article number5604702
Pages (from-to)974-984
Number of pages11
JournalIEEE Transactions on Power Electronics
Issue number2
Publication statusPublished - 16 Jan 2012


  • Driving method
  • LED
  • LED color
  • phosphor-converted (pc) LED
  • white LED

ASJC Scopus subject areas

  • Electrical and Electronic Engineering

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