Record in Efficiency and Brightness for White LEDs

Development engineers at Siemens subsidiary Osram have set a record for the brightness and efficiency of white LEDs. The prototype LED measures one square millimeter and achieves a brightness of 155 lumens at 350 milliamps (standard measuring conditions). This represents an increase in brightness of around ten percent compared to the previous record-holder. The new LED also boasts an efficiency of 136 lumens per watt, also a record. Future applications include general lighting purposes and headlights for cars. Lighting systems that are energy-efficient and thus environmentally compatible are an important element in the Siemens portfolio of environmental products, which generated revenues of €17 billion for the company in fiscal year 2007.

The new semiconductors can also operate at a higher current. At 1.4 amps, for example, these tiny products will generate up to 500 lumens, which is brighter than a 40-watt incandescent bulb. The latter, however, has an efficiency of a mere 15 lumens per watt, which means most of the energy is lost in the form of heat. The new LED, which is now being developed to market maturity, is also significantly more efficient than Osram’s Ostar Lighting LED, which delivers 75 lumens per watt.

For the researchers from Osram Opto Semiconductors, the new record was the result of combining different technologies. To boost brightness, they used an enhanced epitaxial process to apply a thin film of the light-generating substance to the semiconductor substrate. At the same time, they also improved the design of the chip. Last but not least, they optimized the combination of the blue light emitted by the chip itself and the yellow light from the phosphor above, which together produce white light when mixed.

Osram researchers also recently succeeded in improving the robustness and luminosity of organic light-emitting diodes (OLEDs). High in brightness and low in energy consumption, these ultra-thin plastic films have an efficiency of 46 lumens per watt and a service life of more than 5,000 hours.