23 Sep 2015
Organic light-emitting diodes, or OLEDs for short, are flat, homogeneous and energy-efficient flat lighting elements. Their outstanding properties are their extremely thin construction and a two-dimensional radiation characteristic, which differs radically from previous light sources. In addition, they do not require diffusers in order to achieve homogeneous illumination and, unlike LED lights, they do not require any complex thermal management. For the user these properties mean less outlay and a longer lifetime.
Whereas OLED technology has already established itself as a common standard in consumer products, above all flat-screen televisions, smartphones and tablet PCs, OLED illumination in image processing was still a vision of the future until recently. The technology is now ready for the market: in early 2015, hema electronic from Aalen presented its first OLED product – the backlight series seelectorLUX OLED, which is distributed through STEMMER IMAGING.
These backlights, which are dimmable from 0 to 100 percent and feature a light field area of 102 mm x 102 mm with dimensions of 142 mm x 123 mm and a height of just 2.5 mm, are characterised by very high homogeneity and colour fidelity. They operate with a colour temperature of 2500 or 2900 K and exhibit a relatively high Colour Rendering Index of 80. This CRI value describes how much the colour rendering of an illumination deviates from the ideal of daylight. A high CRI value means better colour rendering and leads to advantages in colour applications. CRI values of over 90 can typically be attained with OLEDs, so that OLED-based illumination is particularly well suited to uses in the printing industry and especially in medical applications. It is important for doctors that the colours of pictures taken are as realistic as possible in order to arrive at a reliable diagnosis.
Further features of the first OLED lights from hema electronic are their luminous flux of up to 300 Lumen, an operating temperature from +5 °C to +40 °C and the 24-Volt supply to the intelligent OLED controller box, which is provided by a power supply unit. According to hema, further lighting components such as tunnel lighting and coaxial lights are in preparation.
However, hema electronic is not the only company driving its OLED activities forwards; intensive work towards furthering development of the technology is also progressing on internationally, as Dr. Gotthard Weißflog from OLAB network management in Jena underlines: “The mass production of organic LEDs for lighting applications has begun at OLEDWorks/Philips and LG Chem. Further companies from Germany, such as Osram, as well as those from Japan, China, Taiwan and the USA will follow suit shortly. That should lead to a reduction in the price of OLED components.” Weißflog is convinced that this will also result in new business opportunities for industrial imaging, since imaging technology is absolutely necessary for automation and quality assurance in mass production.
Weißflog says that, like LEDs, there will not be “one” OLED: “LG Chem, for example, is the leader in large formats and now offers an OLED panel with dimensions of 32 cm x 32 cm. Philips, on the other hand, manufactures OLEDs with a luminous intensity of up to 10000 cd/m² and a very low colour point tolerance.”
The first flexible OLEDs can now be ordered from Konica Minolta and LG Chem. Due to the strong interest in flexible OLEDs on the part of the automotive industry, Weißflog is sure that this development direction will come on in leaps and bounds in the coming years. “Flexible OLEDs enable or simplify the development and manufacture of 3D shapes with flat lighting. Innovative system solutions are conceivable here”, says Weißflog, looking to the future.
He points to a further development direction: “Transparent OLEDs, which shine in one direction when switched on, have only been offered so far as laboratory samples. However they basically show new possibilities for compact complete systems consisting of camera, optics and lighting.”
Dr. Tobias Henzler also estimates that “OLED lights will be used increasingly in industrial imaging in the near future due to their interesting features.” The sales employee from STEMMER IMAGING supports the further development of the OLED technology together with Dr. Weißflog and further OLAB networkers and has subjected the latest lights to thorough tests in the laboratory at the Puchheim-based company.
Dr. Henzler reports that the significant results of his investigations include the outstanding overflashing capacity of the OLED lights: “Normal LED modules can be overflashed up to a factor of 10 or 15 at the most, in other words they can be operated with a current that is higher by this factor, resulting in a short-term brighter light radiation.” The tested OLED lights, conversely, can be overflashed up to a factor of 90 and thus generate an extremely bright light, such as is required for demanding applications. “This factor 90 doesn’t mean that OLEDs wouldn’t be suitable for even higher overflashing”, explains Dr. Henzler, “but it represents the limit for commercial flash controllers. The efficiency is reduced and it was clear to us from the start that doubling the current wouldn’t result in a doubling of the brightness, but the fall-off was much less than expected.”
If one assumes the efficiency of the OLEDs to be 100 % in normal operation, then it was still around 50 % with 90-fold overflashing. “We haven't carried out any long-term investigations in our tests, so we don't know whether the operation of OLEDs in this high overflashing region will have a negative effect on their lifetime.” According to Dr. Henzler, however, the test results are very promising and lead to the assumption that OLED lighting could develop into an interesting alternative to LEDs in image processing.
According to Henzler a second result speaks in favour of that: “Unlike LEDs, which shine as points, no hotspot is created because OLEDs work as a light area. That makes thermal management much easier in the application.”