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OLED—raising lighting to a new level

-May 23, 2012

Luminescent carpets and ceilings. Windows that provide bright daylight even when it's dark outside. Glimmering luminescent clothes. When designers and scientists start talking about organic light emitting diodes (OLEDs), their imagination knows no bounds. Indeed, the future holds in store infinite ways of using OLEDs. But even today, these ultra-flat light sources have already managed to raise light to a brand new level. So how are they different from existing light sources? OLEDs are surface light sources, rather than spotlights. Just a mere 1.8 millimeter thick, OLEDs diffuse a warm, pleasant and homogeneous light over the entire surface. More precisely, OLEDs are composed of ultra-thin layers of organic semiconductors and color molecules, which are embedded between two layers of glass. When a voltage is applied, the organic layers begin to light up.

Manufacturing OLEDs involves one of the most high-tech processes around and can be compared with the manufacture of PC chips. It begins with an extremely thin, transparent and electroconductive oxide layer composed of indium tin oxide (ITO) being applied to a glass slide. This layer forms the anode. The subsequent stages of the process involve the application of the organic layers, although the term 'organic' has nothing to do with vegetables or animals in this case. Contrary to LEDs, OLEDs are manufactured using chemically organic material – in other words, carbonate-based components. The final stage incorporates an aluminium cathode, whose prime function is ensuring that the OLED works like a mirror when it is turned off. When voltage is now applied to the OLED, electricity flows from the anode to the cathode and makes the layers in the middle light up. The color that we see depends on the voltage, as well as – more importantly – the material that has been embedded in the organic layers.
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Figure 1 Structure of an OLED.

Surface light sources versus spotlights

The main difference between LEDs and OLEDs is that OLEDs, contrary to LEDs and other common light sources, diffuse their light from the source right across the entire surface, hence the term 'surface light sources'. Light from OLEDs is characterized by a natural softness, whilst diffusing nicely and not dazzling. Due to their extreme flatness – below 1.8 millimeter –, OLEDs can be integrated in many different surfaces and products and allow light sources to be designed in a wide range of shapes and sizes. OLEDs can be fully dimmed right across the spectrum – less electricity means less light, more electricity makes it brighter. No sophisticated electronics are required – standard potentiometers are all that they need.

OLEDs are available in virtually all colors, not to mention in the sphere of high quality white light. Alongside standard shapes, companies such as Philips also provide sophisticated shapes as well as structural OLEDs. As a result, dreams of technical light designs can be given wings very easily. In terms of size, OLEDs have also been gaining ground in recent years, with dimensions exceeding 140 cm² becoming increasingly common. However, for many consumers, the homogeneity of the light is more important than size. With big OLEDs, the "halo" effect (the OLED's darker center and lighter edge) is the restricting factor. This effect occurs because the electricity is always fed in at the edge, with the resistance in the OLED causing the power of the light to weaken as it reaches the center.

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Figure 2
OLEDs generate homogenous light from a flat light source.

Unbeatable energy efficiency

Today, the majority of energy produced is used for lighting buildings. This amount is greatly reduced when energy-saving lighting is used, such as OLEDs. In terms of energy efficiency, organic light diodes are far more advanced than the usual lighting systems. Not only because manufacturing organic components requires less energy than for non-organic components, but also because OLEDs are cold light sources and require less electricity due to their special technology. OLEDs are quick and efficient at converting electrical energy into light, without becoming heating up. In fact, they do not get any warmer than 30 degrees Celsius. As a result, they can be integrated into materials that never used to be associated with light sources, such as straw or paper, for example. The voltage carries no risk either – none of the Philips OLEDs require any more than 14 volts, with a maximum current of 500 mA.

Cars also benefit from new lighting technology

The features that attract designers and architects to OLEDs are the very features that are also winning fans within the car industry. For the first time ever, light applications can be fused together with the vehicle. This paves the way for such features as rear lights that need extremely little casing depth despite their unique shape, giving the car engineer more room for other on-board systems. Or simply more room in the boot, for example. Dreamlike car seats will soon become a reality as they become much more than a simple place to sit. With integrated OLEDs, seats will become sources of light in their own right. The use of Lumiblade OLEDs in the roof lining or on the doorsill provides designers and engineers with brand new ways to introduce lighting into the interior. To a great extent, the light source is concealed within the car, with unsightly, superfluous plastic light casing becoming a thing of the past. The first prototypes from Audi and Smart give us an idea of just how OLEDs can be used. In association with BASF at the last IAA in Frankfurt, carmaker Smart presented a concept study in which transparent OLEDs were combined with transparent solar cells in the roof. A sensational feeling for the passengers of the "smart forvision", with the OLEDs acting as sky lights by day and only lighting up when the door is opened.

Mass-market OLED manufacturing

At the moment, although manufacturing and purchasing OLEDs is more expensive than with usual light sources, technology is continually moving forward with increasing speed. When organic light diodes can be mass-produced – in the not too distant future – the consumer will be able to benefit from the lower prices resulting from increased production. Philips, for example, is already boasting an efficiency and lifespan of up to 45 lumen per watt and 15,000 hours respectively for their Lumiblade OLED brand. A quick comparison: Usual bulbs only achieve a lifespan of 1,500 hours. And that's nothing compared to their efficiency. The halo is also continually improving as a result of advances in technology and has already reached 4000 candela per square meter. Experts predict that indicators will improve two-fold every twelve months.

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Figure 3
OLED production at Lumiblade.

The light of the future, today

The international trend towards sustainability is having an enormous impact on the development of energy-saving light sources. This means that energy-saving lamps and halogen spotlights will gradually disappear from the market. The word on everyone's lips is OLED. The organic light diodes are considered to be THE surface light sources of the future. Experts, architects and designers all believe that OLEDs will be the next big thing in the lighting industry over the next few years. The first products, produced by Philips, for example, are already on the market. The Dutch company's OLEDs can be found in lamp collections such as the "O'Leaf" lighting range by Modular Lighting Instruments or the desk lamp, "Edge", by Establishde&Sons. Admittedly, these are designer lighting collections targeted at the high-end of the market with a price tag of between 800 ($1021) and 2300 euros ($2935) – albeit not completely unaffordable. With these products, Philips is leading the way for future developments within this market. Alongside the traditional uses of standard lighting, OLEDs provide additional ways in which structural lighting (signage) and special lighting can be used. The field of photography will be no exception either, with OLEDs pushing traditional light sources aside when holohedral, homogeneous illumination is needed alongside extremely high quality light. This, in addition to the lack of heat generation, makes OLEDs predestined for such applications.

With products such as the LivingShapes interactive wall, the new light source has already found its way into places such as bars, restaurants, lounges and shops. By means of a hidden sensor, more than 1,000 OLEDs react to what is happening in front of the wall and translate this into luminous OLED spots. The first time people see this kind of wall, they are mesmerized by the fascinating warmth of this natural light. The OLED is also making inroads into the field of functional lighting. Philips recently presented an OLED at the Frankfurt Light + Building exhibition, whose 120 lumen made it the brightest OLED light ever. Which is why, on top of their decorative uses, OLEDs will also be used in practical lighting solutions such as desk lamps, for example.

But one thing is certain: the OLED is just setting out on its journey to fame as a new source of light. It is set to completely transform the way in which we perceive light, allowing new and exciting applications to see light of day, which were, until today, only a figment of our imagination.

Summary: OLED benefits at a glance

  • OLEDs are very thin and are quick and effective at converting energy into light – without the heat. This is why they are ideal for such areas where we have reached the limits of conventional light sources (e.g., macrophotography).
  • OLEDs can be connected to large-scale lighting systems that offer strong, even luminosity OLEDs are available in every possible color.
  • OLEDs provide a beautiful, all-round homogeneous light.
  • OLEDs are extremely energy-efficient and energy-saving.
  • OLEDs are free from harmful substances and are re-usable.

About the author
Dietmar Thomas is the official spokesperson for Lumiblade, Philips' OLED division located in Aachen (Germany). From here, he and his colleagues oversee the worldwide marketing activities for this new lighting technology. Thomas can look back on over 25 years in communication with large corporations, PR agencies, and media in Europe and the United States.

This article was originally published by EE Times.

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