Light-emitting diodes to be the future of light

LED, OLED, FOLED,  electricity efficiency, lighting“LEDs could represent 75% of the lighting market by 2020” according to Christophe Bresson, commercial director of the lighting department at Philips. Such an assumption may sound surprising, given the dominating position of traditional filament lamps and compact fluorescent bulbs on the lighting market, but it is based on the huge electricity efficiency potential of LEDs. Although there is still a great deal of progress to be made, especially with regards to colour rendition, impressive improvements such as flexible and organic LEDs are coming to light. Here is a short overview of a promising, fledgling technology.

How is light efficiency measured?

The electricity or light efficiency of a lighting device is expressed in lumens per watt, a measurement unit expressing the relationship between the light it emits and the power it uses. Traditional incandescent bulbs have a light efficiency of 12 to 20 lm/W, compared with 60 to 100 for compact fluorescent, aka low-energy light bulbs. The light efficiency of LEDs is likely to become twice higher as it is now and reach 150 lm/W, which would make them the undisputed champions of light efficiency!

Technical obstacles and innovations: LEDs, OLEDs and FOLEDs

A LED is an optoelectronic device emitting light (photons) when electric current (electrons) travels through it. Both very efficient and long-lasting, with a lifetime of about 50,000 hours, LEDs, though, suffer from defects which prevent them from winning further market shares. They remain expensive, mainly because of the rare earths they contain, 97% of which are produced in China which controls prices. Besides, their colour rendering index (CRI) is still unsatisfactory.

Organic LEDS or OLEDs are seen as a major innovation. They contain layers of organic semiconductors, that is made from carbon (crystals and polymers, as opposed to inorganic semiconductors such as silicon), located between two electrodes, one of which at least transparent. OLEDs have the dual benefit of being made of cheaper materials and generating light on thin and extensive layers. When built on a flexible plastic substrate, they become soft: FOLEDs (for Flexible Organic Light-Emitting Diodes) open up a host of unsuspected possibilities for tomorrow’s electronics (soft and foldable screens, lighting wallpaper, etc.)

However, two hurdles remain: the light yield of OLEDs is far below this of traditional LEDs so far, and their lifetime is relatively limited (14,000 hours).

Such drawbacks make some experts assume that by 2020 OLEDs will only find use in niche applications on the broader lighting market, such as defence equipment for instance. Although they are still too expensive to conquer the mainstream market, OLEDs represent a dramatic improvement in modern lighting.

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