Improving LED Light Output and Efficacy Through SPE™

Commercial white LEDs combine a light-emitting semiconductor with a phosphor to produce visible white light. The nature of most phosphors, however, causes more than half of the light, or photons, generated to divert back toward the semiconductor die, where much of it is absorbed and lost. This scattering reduces the LED’s overall light output.

In 2004, LRC researchers developed Scattered Photon Extraction (SPE™), a method to improve the light output and efficacy of white LEDs. The SPE method combines optimally shaped optics and placement of the phosphor away from the die. This configuration allows light traveling back toward the die to escape through the sides of the optics, generating 30 to 60 percent more light output (lumens) and luminous efficacy (lumens per watt of electricity) than typical white LEDs. Moreover, moving the phosphor layer away from the semiconductor die improves LED life.

Since the development of SPE, a number of other LRC studies have used this method to:

• Improve the spatial color uniformity of mixed-color LED systems
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• Optimize performance through optical ray-tracing
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• Understand the effects of phosphor layer order in multiple-phosphor LED packages
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• Develop a snap-in LED module for outdoor luminaires
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• Design a better recessed downlight
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• Investigate the use of multiple phosphors in layers
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• Analyze phosphor treatments to close the LED "green gap"
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• Build an LED replacement for linear fluorescent lamps
  

This study was part of a larger project funded by the U.S. Department of Energy: High-Efficiency, Nitride-Based Solid-State Lighting

Technical Reports and Publications

Narendran, N., Y. Gu, J.P. Freyssinier-Nova, and Y. Zhu. 2005. Extracting phosphor-scattered photons to improve white LED efficiency. phys. stat. sol. (a) 202 (6): R60-R62.
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Narendran, N. 2005. Improved performance white LED. Fifth International Conference on Solid State Lighting, Proceedings of SPIE 5941: 45-50.
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Wu, H., N. Narendran, Y. Gu, and A. Bierman. 2007. Improving the performance of mixed-color white LED systems by using scattered photon extraction technique. Seventh International Conference on Solid State Lighting, Proceedings of SPIE 6669: 666905.
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Zhu, Y., and N. Narendran. 2008. Optimizing the performance of remote phosphor LEDs. Journal of Light and Visual Environment 32(2): 115-119.
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Zhu, Y., and N. Narendran. 2010. Investigation of remote-phosphor white light-emitting diodes with multi-phosphor layers. Japanese Journal of Applied Physics 49: 100203.
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Zhu, Y., P. Dutta, and N. Narendran. 2010. Post-synthesis annealing effects on SrGa2Se4:Eu2+ phosphors with peak emission wavelength in the green gap. Tenth International Conference on Solid State Lighting, August 1-5, 2010, San Diego, CA, Proceedings of SPIE 7784: 77840P.
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Project Summary Sheets

LED Replacement for Linear Fluorescent Lamps (2013)

Designing a Better Recessed Downlight Using SPE Technology (2010)

Snap-in LED Module for Outdoor Luminaires (2010)

Techniques to Improve Green Phosphor for Superior White LEDs (2010)

White SPE LEDs with Multi-phosphor Layers (2010)

Optimizing Remote-phosphor LEDs with Optical Ray-tracing (2009)

SPE Technology for Mixed-Color LEDs (2007)

'SPE' Method Enhances White LED Light Output (2005)

Patent Information

Sponsors

The Link Foundation, Energy Fellowship Program
United States Department of Energy, Cooperative Agreement No. DE-FC26-01NT41203
University of California at Santa Barbara