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Virtual Journal for Biomedical Optics

Virtual Journal for Biomedical Optics


  • Editors: Andrew Dunn and Anthony Durkin
  • Vol. 8, Iss. 5 — Jun. 6, 2013

Broadband mean free path of diffuse light in polydisperse ensembles of scatterers for white light-emitting diode lighting

Willem L. Vos, Teus W. Tukker, Allard P. Mosk, Ad Lagendijk, and Wilbert L. IJzerman  »View Author Affiliations

Applied Optics, Vol. 52, Issue 12, pp. 2602-2609 (2013)

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We study the diffuse transport of light through polymer slabs containing TiO2 scattering particles. The slabs are diffuser plates typical of a commercial white light-emitting diode (LED) module (Fortimo). We have measured the diffuse transmission and reflection properties over a broad wavelength range (470–840 nm) from which we derive the transport mean free path using the theory of light diffusion. With increasing scatterer density, the mean free path becomes shorter. The mean free path increases with wavelength; hence, blue light is scattered more strongly than red light. To interpret the results, we propose an ab initio model without adjustable parameters for the mean free path by using Mie theory. We include inhomogeneous broadening as a result of the size distribution of the scattering particles as measured by dynamic light scattering. Surprisingly, the calculated mean free path decreases with wavelength, at variance with our experiments, which is caused by particles with radii R in excess of 0.25 μm. Close inspection of the scatterers by electron microscopy reveals that large particles (R>0.4μm) consist of clusters of small particles (R<0.13μm). Therefore, we have improved our model by only taking into account the individual scatterers within the clusters. This model predicts mean free paths in good agreement with our experimental results. We discuss consequences of our results to white LED lighting modules.

© 2013 Optical Society of America

OCIS Codes
(230.3670) Optical devices : Light-emitting diodes
(290.4020) Scattering : Mie theory
(290.4210) Scattering : Multiple scattering
(290.5850) Scattering : Scattering, particles
(290.7050) Scattering : Turbid media
(160.4236) Materials : Nanomaterials

ToC Category:
Optical Devices

Original Manuscript: November 13, 2012
Revised Manuscript: February 1, 2013
Manuscript Accepted: February 8, 2013
Published: April 15, 2013

Virtual Issues
Vol. 8, Iss. 5 Virtual Journal for Biomedical Optics

Willem L. Vos, Teus W. Tukker, Allard P. Mosk, Ad Lagendijk, and Wilbert L. IJzerman, "Broadband mean free path of diffuse light in polydisperse ensembles of scatterers for white light-emitting diode lighting," Appl. Opt. 52, 2602-2609 (2013)

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