Our readers are familiar with many concepts of LED lighting and LEDs in general. This time we will shortly introduce the organic LED or OLED, its main features and applications. OLEDs are not generally used for lighting purposes, but new products and techniques are being developed.
Every week LEDcentre.uk.com tries to provide some new information on LED lighting, and we haven’t mentioned OLEDs (Organic Light Emitting Devices), which are creeping into our everyday lives, even if we don’t hear this term mentioned too often. OLEDs are not primarily used as lighting devices, but rather as displays. For their use as a main source of lighting further improvements are necessary. But how is OLED different from a simple LED?
OLEDs are organic light emitting diodes, so their components include organic substances which emit light once current runs through them. They can be either mono-layered or more often multi-layered, and also contain a usually transparent cathode and anode at the two ends for transporting current.
Organic LEDs are, basically the futuristic way of lighting, and their range of application widens continuously. The reason for their popularity is due to their exclusive features, which can be used advantageously not only in the lighting industry, but at the moment primarily in manufacturing displays of all forms (TVs, mobiles, adverts). These displays may contain PMOLED or passing matrix addressing schemes or AMOLEDs – active matrix schemes. AMOLEDS with film transistor backplanes make it possible to switch or address each pixel individually, in other words touch screen.
Other advantages include its very small size, as OLEDs are layered on a thin film, or other paper-thin sheets. They are also very light due to this, with the flexibility of plastic substances. Beside the physical features, the displayed images on OLED have a higher brightness, better power efficiency in general, and a wide viewing angle. OLED displays are generally brighter with more lively (sometimes even considered unnatural) sharpness and liveliness of the colours. Also, these panels do not require back lighting, as previous side-lighted or back-lit panels, so black colours can be fully displayed on them, as perfect solution for advertising panels.
On the other hand, OLED technology is still in its infancy, and new solutions appear on the market constantly. There are plenty of issues that need research for it to become a reliable, long-term solution for either lighting or displays. One of its disadvantages is its rather short lifespan. Blue OLED components only have the lifetime of 14 000 hours, which is about 8 years with regular use of the display. This is too little compared to current solutions available on the market (LED, LCD), and more expensive as well. Also, since blue components lose their lifespan faster than other components, their visibility is a difficulty. Blue light is more difficult to detect by the human eye, so they need to be generally more powerful. The problem has been solved so far with optimizing the colour ratio within a pixel, to balance out the differences in lifespan. Also blue light is set as more intensive, often resulting in an artificial-looking picture on the display. Further issues can be water resistance (as OLEDs are ruined by water instantly, so their outdoor performance hugely depends on the construction’s IP rating); the high power consumption of white light displays; or screen burn-in, which can happen due to the differing lifespan of the colours.
Naturally what we are primarily interested in is the technology’s application for lighting purposes. This application of OLEDs has only started, since the generally low performance of these diodes and their current short lifespan prevents manufacturers to use it as a main source of lighting. Also, the manufacturing of OLEDs has just started in larger amounts, which will hopefully lead to a reduction of its price. Demand for organic LEDs is growing constantly, due to additional applications by mobile phone companies and display manufacturers.
As for lighting, OLED as a new form of lighting offers entirely new solutions. Since OLEDs could even be printed on a sheet of paper even, they are recently applied as wallpaper with background lighting. Its transparency allows it to be used as window during daytime and source of light as a panel during the night. Novaled OLED panels bear a 60-70% transparency.
For commercial purposes the first product was the round Orbeos OLED panel by Osram in November 2009. Although due to the current problems with these applications we will still have to wait until OLED becomes a competitive lighting source, its generally peculiar features and the new solutions they allow will bring new light to our homes.
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