Imitating Broad-Band Diurnal Light Variations Using Solid State Light Sources

Dr. Ian Ferguson
Professor, School of Electrical and Computer Engineering, Georgia Tech

Date: Wednesday, October 3, 2007 at 12:00 PM
Room: EDRB 38

Abstract

The use of light emitting diodes (LEDs) in lighting, also known as solid state lighting (SSL), has been successful in niche markets such as signage and displays, but no significant penetration has been achieved in the general illumination market. LEDs have advantages over conventional light sources, such as higher efficiency, longer life, smaller size, and enhanced controllability. The smaller size and controllability offer designers more freedom to create novel devices and fixtures while adding new functionality to lighting systems. However, in general illumination different criteria such as a high color rendering capability, and appropriate correlated color temperature make a SSL solution more difficult to construct. Currently, no available SSL technologies incorporate all the necessary attributes for general illumination. Thus, there is a need for the development of novel sources that offer new features rather than an equivalent replacement for traditional light sources. The current status of the development on a new, phosphor free, solid state light source based on hybrid GaN-ZnO will the discussed. General illumination requires high color rendering capability and appropriate color temperature. Therefore, it is important to eliminate gaps in the power spectrum of typical LED sources to achieve high quality white light. The power spectrum obtained using clusters of RGB (red-green-blue) LEDs display gaps which can be better controlled by tuning of the blue source. Tuning will allow more control of the broadband source over a 24 hour period, imitating broadband diurnal light variations. A broadband spectrally dynamic solid state illumination source has been developed. This new device is comprised of a three or two terminal dual LED structure. Separate control of two MQW regions can be achieved in this arrangement with a tunnel junction acting as a buried current spreading layer. A combination of multiple phosphors are then “pumped” by either or both of the wavelengths emitted from the dual LED to produce white light of a variable power spectrum. The correlated color temperature of the emitted white light can be controlled by adjusting the relative intensities of the two pump wavelengths. Innovations such as this will help solid state illumination sources gain a competitive advantage over conventional illumination sources. The physiological implementation of SSL on the human circadian rhythm will also be discussed.

Presenter Bio

Ian T. Ferguson is a Professor in the School of Electrical and Computer Engineering at Georgia Institute of Technology (Georgia Tech) and Director for the Focused Research Center Next Generation Lighting. His research focuses on the area of wide band-gap materials and devices (emitters, detectors and electronics) using GaN and ZnO and developing these materials for illumination and spintronic applications. He has over 200 refereed publications, six book chapters, edited ten conference proceedings, two books and multiple patents. He teaches undergraduate, graduate and short courses on solid state lighting and illumination engineering and will publish a book on ‘Solid State Illumination and Illumination Engineering’ in 2007. He founded the International Conference on Solid State Lighting which is now in its seventh year and recently completed the Festival of Lights USA.