Smart lighting may replace common light bulb in coming years

January 14th, 2009 - 4:42 pm ICT by ANI  

Washington, January 14 (ANI): The common light bulb may become history in coming years, thanks to researchers at Rensselaer Polytechnic Institute in New York who have significantly improved the lighting performance and energy efficiency of light emitting diode (LED).
The significance of the breakthrough work lies in the fact that supplanting the common light bulb by a new wave of lighting devices based on LEDs and solid-state lighting may lead to vast environmental, energy, and cost benefits as well as innovations in healthcare, transportation systems, digital displays, and computer networking.
Working in collaboration with experts from Samsung Electro-Mechanics, the researchers have achieved an 18 percent increase in light output and a 22 percent increase in wall-plug efficiency, which essentially measures the amount of electricity the LED converts into light.
The researchers have revealed that the new type of LED achieves a notable reduction in efficiency droop, a well-known phenomenon that provokes LEDs to be most efficient when receiving low-density currents of electricity, but then to lose efficiency as higher density currents of electricity are fed into the device.
While the cause of this droop is not yet fully understood, some studies have suggested that electron leakage may be a large part of the problem.
This droop is under the spotlight since todays high-brightness LEDs are operated at current densities far beyond where efficiency peaks, said project leader E. Fred Schubert, Wellfleet Senior Constellation Professor of Future Chips at Rensselaer, and head of the universitys National Science Foundation-funded Smart Lighting Engineering Research Center.
This challenge has been a stumbling block, because reducing the current densities to values where LEDs are more efficient is unacceptable. Our new LED, however, which has a radically re-designed active region, namely a polarization-matched active region, tackles this issue and brings LEDs closer to being able to operate efficiently at high current densities, Schubert said.
Schuberts team focused on the active region of LEDs where the light is generated, and found that the region contained materials with mismatched polarization.
He said that the polarization mismatch likely causes electron leakage, and therefore a loss of efficiency.
He and his colleagues found that the polarization mismatch could be strongly reduced by introducing a new quantum-barrier design.
The researchers replaced the conventional Gallium Indium Nitride/Gallium Nitride (GaInN/GaN) layer of the LED active region, and replaced it with Gallium Indium Nitride/ Gallium Indium Nitride (GaInN/GaInN).
The substitution allowed the layers of the active region to have a better matched polarization, and in turn reduced both electron leakage and efficiency droop.
The benefits seen by testing the new GaInN/GaInN LED were consistent with theoretical simulations showing polarization matching reducing electron leakage and efficiency droop.
An article on this study has been published online this week by Applied Physics Letters. (ANI)

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