Jim Franklin

Earp, A.A., Franklin, J.B. & Smith, G.B. 2011, 'Absorption tails and extinction in luminescent solar concentrators', Solar Energy Materials And Solar Cells, vol. 95, no. 4, pp. 1157-1162.
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Non-ultraviolet (UV) photoexposure of luminescent solar concentrators (LSC's) can produce photoproducts that cause additional extinction at wavelengths somewhat longer than the main dye absorption peak. This photo-induced 'tails' extinction is deleterious to luminous output in collectors of useful lengths. An experimental method that enables the subdivision of tails extinction in an LSC into absorbed and scattered components is described. The relevant theory is outlined, and experimental results are presented for a polymethyl methacrylate (PMMA) LSC containing Lumogen F083 dye. For this sample, tails absorption increased significantly with outdoor exposure, while tails scattering remained constant. Further measurements indicate that LSC luminous output is around five times more sensitive to tails absorption than to fluorescence quenching. This work also indicates that merely checking for dye quenching, as is often done, can be a misleading indicator of long-term LSC output.

Earp, A.A., Rawling, T., Franklin, J.B. & Smith, G.B. 2010, 'Perylene Dye Photodegradation Due to Ketones and Singlet Oxygen', Dyes and Pigments, vol. 84, no. 1, pp. 59-61.
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The photodegradation rate of a perylene dye (Lumogen F Yellow 083) in methyl isobutyrate was found to increase with ketone concentration for two different ketones. Of the ketones employed, methyl pyruvate, an impurity in methyl methacrylate, was found to be particularly deleterious to dye stability. In agreement with other published studies, the addition of the anti-oxidant DABCO (1,4-diazabicyclo-[2.2.2] octane) to the dye matrix was found to increase dye stability; however when ketones were present, DABCO lead to increased photodegradation. These results highlight the importance of removing ketone impurities from dye matrices during production of Luminescent Solar Concentrators (LSCs).

Earp, A.A., Smith, G.B. & Franklin, J.B. 2007, 'Simplified BRDF Of A Non-lambertian Diffuse Surface', Lighting Research and Technology, vol. 39, no. 3, pp. 265-281.
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For real diffuse surfaces, the bi-directional reflectance distribution function (BRDF) is non-Lambertian, and may require a more complex model in ray tracing simulations. The BRDF of a diffuse white surface is studied at multiple angles of incidence, and

Deller, C.A., Franklin, J.B. & Smith, G.B. 2006, 'Monte Carlo ray-tracing in particle-doped light guides', Lighting Research and Technology, vol. 38, no. 2, pp. 95-108.
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A general Monte Carlo ray-tracing method for light guides with particles randomly dispersed in a matrix is presentedd. Previous ray-tracing approaches have been designed for undoped cylindrical light guides, where a propagating ray is deviated bu total internal reflection only. These geometrical principles are extended and further developed into a method of ra-tracing suitable for particle-doped systems. Redefining ray direction after deviation by a particle, obtaining ray/wall intercept points and angles, and calculation of ray reflection angles from a cylindrical surface are described. Simulations of light from a source LED traced through TRIMM-doped (Transparent Refractive Index Matched Micro-Particle) polymethyl methacrylate (PMMA) light guides have been performed. Distributions of the light exiting the walls of two concentrations of TRIMM-doped lgith guides are given, as an exampled of an application of the described ray-tracing method.

Swift, P.D., Smith, G.B. & Franklin, J.B. 2006, 'Hotspots in cylindrical mirror light pipes: description and removal', Lighting Research and Technology, vol. 38, no. 1, pp. 19-31.
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The transmittance and irradiance distribution at the exit aperture of a cylindrical mirror light pipe (MLP) have been measured and calculated for the cases of collimated and diffuse inputs. MLPs are an example of a nonimaging optical system that can concentrate light, which may give rise to problematic hotspots and glare either on any diffuser used at the exit aperture or in the illuminated room. It is shown in this work that use of a diffuser at the entrance aperture overcomes these problems without a marked reduction in transmission of a typical MLP.

Deller, C.A., Smith, G.B. & Franklin, J.B. 2004, 'Colour mixing LEDs with short microsphere doped acrylic rods', Optics Express, vol. 12, no. 15, pp. 3327-3333.
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The output colour distributions from red, green and blue (RGB) LEDs mixed with cross linked PMMA micro particle doped PMMA mixing rods is compared to output from a plain PMMA mixing rod. Distinctive patterns with clear colour separation result with the undoped rod. These are homogenised by our mixers, resulting in white light. Light output has been photographed, measured and computer simulated at a distance of 10 cm from the output end of the rods.

Earp, A.A., Smith, G.B., Swift, P.D. & Franklin, J.B. 2004, 'Maximising the light output of a Luminescent Solar Concentrator', Solar Energy, vol. 76, pp. 655-667.
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Earp, A.A., Smith, G.B., Franklin, J.B. & Swift, P.D. 2004, 'Optimisation of a three-colour luminescent solar concentrator daylighting system', Solar Energy Materials and Solar Cells, vol. 84, pp. 411-426.
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Smith, G.B., Jonsson, J.C. & Franklin, J.B. 2003, 'Spectral and global diffuse properties of high-performance translucent polymer sheets for energy efficient lighting and skylights', Applied Optics, vol. 42, no. 19, pp. 3981-3991.
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A visible and near-IR spectral study is presented for a translucent smooth polymer sheet in which dopant particles are clear polymer with a refractive index close to that of the clear polymer host. Diffuse, specular, and total reflectance and transmittance and absorptance as a function of sheet thickness and dopant levels approach ideal behavior for lighting applications. A fourth optical parameter, side loss ST, is introduced to fully account for the measured data. This covers radiation that is trapped by total internal reflection (TIR) and travels sideways sufficiently far, including to the sheet+s edges, to miss detection on exit. ST has a strong spectral character, whereas total T and R spectra closely follow the spectrally flat wavelength dependence of the undoped clear sheet. Three distinct regimes are identified for the behavior with wavelength of the specular and diffuse components and are linked to rear surface TIR and side loss

Smith, G.B., Earp, A.A., Stevens, J., Swift, P.D., McCredie, G.M. & Franklin, J.B. 2000, 'Materials Properties for Advanced Daylighting in Buildings', Sayish AAM, vol. 6, no. 1, pp. 201-206.
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Some recent developments in materials used to illuminate interior and exterior spaces with daylight, and mathematical modelling of their interaction with light for design purposes are presented. The Sydney 2000 Olympic Stadium roof and a new solid light guide system are two examples. Emphasis is on making full use of the daylight resource, not just the diffuse component, while controlling the associated solar heat gain. Sensitivity to glare is essential if materials capabilities are to be realised.

Deller, C.A. & Franklin, J.B. 2005, 'Optimising the length of doped polymer light mixers', National Congress of the AIP, Canberra, Australia, January 2005 in Proceedings of the 16th National Congress of the Australian Institute of Physics, ed Colla, M, Australian Institute of Physics, Canberra, Australia, pp. 84-87.
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Transparent Refractive Index Matched Micro-particles (TRIMM) in polymer rods are highly efficient light mixers. This paper addressess the problem of estimating the optimum length fr the mixing rods, for a given TRIMM-to-matrix refractive index ratio and concentration. Light mixing can be this maximised and loss minimised, without computer ray tracing simulations. The probability density function and mean angle for a single TRIMM sphere ray deviation are derived and used in modelling an expression for a critical mixer length for rays of normal incidence. Similar models could be very useful design tools with further development.

Earp, A.A., Franklin, J.B. & Smith, G.B. 2005, 'Extraction of trapped light from luminescent solar concentration', National Congress of the AIP, Canberra, Australia, January 2005 in Proceedings of the 16th National Congress of the Australian Institute of physics, ed Colla, M., Australian Institute of Physics, Canberra, Australia, pp. 104-107.
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In modern light sources such as Luminescent Solar Concentrators (LSC's) and Light Emitting Diodes (LED's), light is emitted within a light-guiding structure of high refractive index. Some of this light is trapped and will not be able to escape. Similar problems are observed when collecting fluorescent radiation in waveguides (1) and scintillation detectors (2). For lighting applications, this trapped light should be ablet o escape the light-guiding structure. In LED's this is commonly achieved witha special profile in the active zone. However, inLSC's the small light-emitting zone is remote from the large light collector so a different approach must betaken. This paper will focus on the extraction of emitted light from rectangular LSc's and propose a way of extracting a large fraction of the trapped light.

Deller, C.A., Smith, G.B. & Franklin, J.B. 2004, 'Uniform white light distribution with low loss from coloured LEDs using polymer doped polymer mixing rods', SPIE Annual Meeting: Optical Systems Engineering, Denver, USA, August 2004 in SPIE Annual Meeting 2004: Optical systems engineering, ed McCall; M., SPIE, USA, pp. 231-239.
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Deller, C.A., Smith, G.B., Franklin, J.B. & Joseph, E.K. 2002, 'The integration of forward light transport and lateral illumination of polymer optical fibre', Congress of the Australian Institute of Physics, Sydney, Australia, July 2002 in Proceedings of the Australian Institute of Physics 15th Biennial Congress 2002., ed Neilson D, Causal Productions Pty Ltd, Adelaide, pp. 307-309.
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Smith, G.B., Earp, A.A., Franklin, J.B., McCredie, G.M. 2001, 'Novel high-performance scattering materials for use in energy saving light fittings and skylights based on polymer pigmented with polymer', Solar and Switching Materials, San Diego, August 2001 in Solar and Switching Materials, ed Lampert, Granqvist, Lewis, SPIE, Bellingham WA USA, pp. 10-18.
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Simple quantitative performance criteria are developed for translucent materials in terms of hemispherical visible transmittance, and angular spread of transmitted luminance using a half angle. Criteria are linked to applications in luminaires and skylights with emphasis on maximising visible throughput while minimising glare. These basic criteria are also extended to angle of incidence changes which are substantial. Example data is provided showing that acrylic pigmented with spherical polymer particles can have total hemispherical transmittance with weak thickness dependence, which is better than clear sheet, while the spread of transmitted light is quite thickness-sensitive and occurs over wider angles than inorganic pigments. This combination means significantly fewer lamps can achieve specified lux levels with low glare, and smaller skylights can provide higher, more uniform daylight illuminance.