Home | English | 简体 | 繁體 | UGC | Font Size: A A A

  Dynamic Optimization of Power Flow and Electric Vehicle Resources in Smart Grid

  Mass Transport in the Nano-structured Electrode of Polymer Electrolyte-based Fuel Cells

  Smart Grid

  LED Replacement Lamp Driver with Universal Compatibility

  Sustainable Lighting Technology: From Devices to Systems

  Exploiting Strain-relaxed Quantum Wells for Broadband Emission LEDs

Members of the joint HKU and PolyU research team

Lighting systems consume about 18% of electricity globally. This project focuses on "sustainable lighting technology". It clarifies the important concept that "energy saving is not necessarily environmentally friendly", unless the technology has long lifetime and a large portion of the product materials is recyclable. The research team is therefore promoting a new "Sustainability" concept involving three criteria, namely (1) energy saving, (2) long product lifetime and (3) recyclability. The recent advancement in Light-Emitting Diode (LED) technology provides a platform for fulfilling these three sustainability criteria for lighting applications.

LED devices are known for their high luminous efficiency and long lifetime (typically 6 to 8 years). However, the bottleneck of traditional electronic drivers for LED systems is their relatively short lifetime of typically 3 years – limited by the lifetime of a component called electrolytic capacitor. For outdoor applications, extreme weather conditions such as wide temperature changes and lightning are also major factors restricting the lifetime of LED products.

This Theme-based Research Project is jointly carried out by the HKU team (led by Prof Ron HUI) and PolyU team (led by Prof Michael TSE). After intensive research for the first two years of the project period, we have achieved the following:
  • The development of a new LED device structure with low thermal resistance
    Heat and light are enemies to each other in LED technology. In order to maximize the light output, it is necessary to design an LED device structure that has low junction temperature. In other words, a good LED device structure should be one that allows heat to flow out of the device easily. We have developed a new LED device structure with good thermal performance. Consequently, high light output from LED devices becomes feasible.
  • The development of patent-pending "passive" LED drivers that can fulfil the three sustainability criteria
    This technology has been adopted by a Hong-Kong-based company in the production of passive LED street lamps. These lamps have a high energy efficiency exceeding 92%, a designed lifetime exceeding 10 years and 80% of the product materials being recyclable. It is envisaged to be the world’s first LED street lamp product of which the LED driver’s lifetime exceeds that of the LED device. Therefore, this technology is ideal for outdoor applications.

  • The development of "active" LED drivers that are free of electrolytic capacitors
    Without any electrolytic capacitors, the bottleneck in the lifetime restriction of LED drivers can be removed. New compact LED products with high efficiency and long lifetime for indoor applications become possible.

  • New colour and dimming control
    Colour and dimming control are important functions of LED systems. In the past, dimming control of LED systems inevitably affects the colour temperature. We have now developed new techniques that can separate colour and dimming control so that colour temperature control can be achieved at a constant light intensity; and light intensity can be controlled at a constant colour temperature.

  • Extended LED system theory
    On the theoretical aspects of the project, we have successfully developed a Unified Theory linking the interactions of (i) Heat, (ii) Light, (iii) Electric Power and (iv) Colour in LED systems. This theory has become a design tool for optimizing LED systems for a wide range of products. One can now predict the light intensity and colour variations of an LED system before building the product.

Prof Ron Shu Yuen HUI
Department of Electrical and
Electronic Engineering

The University of Hong Kong