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HKTDC Hong Kong Lighting Fair 2011 (Spring Edition) Seminar
OLED Shining On Lighting

  LED lighting was one of the leading trends at the HKTDC Hong Kong International Lighting Fair 2011 (Spring Edition)
  LED lighting was one of the leading trends at the
HKTDC Hong Kong International Lighting Fair 2011
(Spring Edition)
Organic light emitting diode (OLED) technology is brightening the lighting industry by cutting production costs, increasing design flexibility and lengthening device lifespans, according to a Hong Kong scientist.

“OLED is widely expected to be the next generation of products that will likely revolutionise the whole concept of lighting,” predicted Professor Zhu Furong of the Department of Physics and Centre for Advanced Luminescence Materials at the Hong Kong Baptist University.

He was speaking at a symposium entitled “Lighting 2011 – New Materials and Technologies” at the HKTDC Hong Kong International Lighting Fair 2011 (Spring Edition).

Professor Zhu said that an OLED — a light emitting diode (LED) in which the electroluminescent layer is made of organic semiconductor compounds — had a string of advantages over inorganic LEDs, including:

  • a surface light source rather than a point source
  • simpler manufacturing process
  • easier and less expensive to use in large areas
  • a flexible form
  • transparent light possible
  • little heat

The OLED was discovered in a useful form by Kodak in 1989, while the first OLED product hit the market in 1998, recounted Professor Zhu. “Today, OLED is a whole new industry with applications that include displays and lighting,” he explained, adding that the technology enables novel lighting panels, signage and keypad illumination to be produced at low cost.

“OLED is definitely the next wave in solid-state lighting (SSL),” Professor Zhu remarked. SSL refers to lighting that uses LEDs as illumination sources rather than electrical filaments, plasma or gas.

He noted that OLED lighting was evolving fast, with a global market forecast to be worth US$40bn by 2016. “The OLED is still in the early stages of development, but it is steadily and increasingly penetrating the lighting market,” he said. “Unlike inorganic LEDs and fluorescent tubes, OLEDs require no diffusers or light guide plates and therefore offer higher efficacy.”

Professor Zhu added that researchers would continue to enhance the OLED, which currently has a shorter lifespan than the inorganic LED.

Most lighting OLEDs being used at present are white-light OLEDs (WOLEDs) in signage and glass tiles, although the sector is increasingly seeing OLEDs with tunable colours and brightness, transparent OLEDs, all shapes of OLEDs and even flexible OLEDs.

Professor Zhu highlighted the advances in WOLED lighting. “WOLED is an encouraging and promising new lighting technology, offering high potential for new lighting markets,” he said.

“WOLED devices are expected to achieve an efficacy of 100-150 lm/W in the long run. WOLED products are thin, flexible and suitable for large-area lighting.”

WOLEDs are applied in large lighting panels measuring, for example, 30x30cm, and have been used in OSRAM lighting panels, Matsushita Electric’s electroluminescence lighting and Konica Minolta’s first flexible OLED lights that were launched in 2010.

Professor Zhu also cited the example of Universal Display Corp’s 5x5cm WOLED device featuring an efficacy of 68 lm/W, a lifetime of more than 10,000 hours and a colour rendering index of 80.

Major lighting manufacturers including OSRAM, Philips, Lumiotec, GE and Konica Minolta have announced mass production of WOLED products, he added.

“Nevertheless, the WOLED is facing several challenges, such as how to achieve high efficacy at high luminance, how to attain a high colour rendering index, stable colour quality, large-area lighting uniformity, a longer lifespan and even lower costs,” he said.

Transparent OLEDs, meanwhile, allow for special lighting applications, such as on windows or furniture with transparent or translucent elements, advised Professor Zhu.

 

Dazzling Displays

OLEDs are also used in a range of electronic displays such as TV, computer, mobile phone and PDA screens.

Compared with LCDs, OLED displays offer:

  • a higher contrast ratio (more than 10,000:1)
  • a shorter response time (less than 0.1millisecond)
  • a wider viewing angle (greater than 170 degrees)
  • a slimmer total thickness (less than 1.5mm )
  • lower power consumption (less than 50% of that of LCDs)

“Most important of all, the OLED has a simpler structure that significantly reduces manufacturing costs,” said Professor Zhu.

“OLED displays will have a growing market share for portable applications thanks to their image quality, slimness and light weight.”

He said the OLED offers potential benefits for future display technology, including:

  • new product design opportunities
  • portable devices with large, storable displays
  • lightweight and robust structures
  • lower production costs

“OLED-based displays are likely to replace LCDs in many applications including mobile phones, palm tops, digital cameras, PDAs and TVs. Some small-sized matrix-driven OLED displays are already available in the market,” observed Professor Zhu.

“But it is clear that OLEDs must deliver an even greater cost advantage to become the mainstream as LCDs continue to improve.”

OLED displays use either active-matrix or passive-matrix addressing schemes.

With passive-matrix OLEDs (PMOLEDs), the display is controlled by switching on rows and columns to light the pixel at the intersection.

Active-matrix OLEDs (AMOLED), by contrast, require a thin-film transistor backplane to switch each individual pixel on or off, enabling higher-resolution and larger displays.

“PMOLED technology is mature and widely recognised in the market,” advised Professor Zhu. “On the other hand, AMOLEDs are making promising progress and are already used in TVs supplied by Sony, Toshiba, Samsung and LG Philips.”

AMOLED TVs emerged in the 2000s and are expected to continue their uptrend in the coming decades until at least the 2030s, according to Display Bank graphs presented by Professor Zhu.