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Padova, Italy

Trivellin N.,LightCube SRL | Trivellin N.,University of Padua | Meneghini M.,University of Padua | Dal Lago M.,University of Padua | And 4 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

With this work we report on the performance and degradation mechanism of commercially available remote phosphors (RP) for SSL. Thermal analysis indicates that phosphors can reach temperatures above 60°C during operation at an ambient temperature of 25°C when subjected to an optical power of 346 mW/cm2. We also demonstrate that temperature is a strong driving force for the degradation. Results indicate a gradual reduction in luminous flux output and a decrease of correlated color temperature as a consequence of stress. We demonstrate that the degradation rate is strongly correlated with stress temperature with an activation energy of 1.36 eV for a TTF of 70%. © 2013 SPIE.


Meneghini M.,University of Padua | Dal Lago M.,University of Padua | Rodighiero L.,University of Padua | Trivellin N.,LightCube SRL | And 2 more authors.
Microelectronics Reliability | Year: 2012

This paper describes an extensive analysis of the degradation of high-power white LEDs, submitted to dc and pulsed stress. By means of combined electrical and optical characterization we provide experimental evidence for the following: (i) dc stress can induce a significant decrease in the luminous flux of the devices; (ii) degradation rate has a linear dependence on the stress current level, thus indicating that current is a major driving force for degradation; (iii) optical degradation is significantly correlated to the increase in the defect-related current components, and to the red-shift of the emission wavelength of the main blue peak. On the basis of these results, degradation is ascribed to the increase in the defectiveness of the active region, with subsequent generation of defective or shunt paths; (iv) PWM stress determines a stronger degradation with respect to dc stress, for devices aged under similar conditions. The different mechanisms that may contribute to increasing the degradation rate during PWM stress with respect to dc case are discussed in the paper. © 2011 Elsevier Ltd. All rights reserved.


Trivellin N.,LightCube SRL | Trivellin N.,University of Padua | Meneghini M.,University of Padua | Ferretti M.,University of Padua | And 4 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

Color temperature, intensity and blue spectrum of the light affects the ganglion receptors in human brain stimulating the human nervous system. With this work we review different methods for obtaining tunable light emission spectra and propose an innovative white LED lighting system. By an in depth study of the thermal, electrical and optical characteristics of GaN and GaP based compound semiconductors for optoelectronics a specific tunable spectra has been designed. The proposed tunable white LED system is able to achieve high CRI (above 95) in a large CCT range (3000 - 5000K).


De Santi C.,University of Padua | Dal Lago M.,LightCube SRL | Buffolo M.,University of Padua | Meneghini M.,University of Padua | And 2 more authors.
2015 IEEE 1st International Forum on Research and Technologies for Society and Industry, RTSI 2015 - Proceedings | Year: 2015

This paper describes one of the first studies of the degradation of retrofit light bulbs based on white GaN light emitting diodes. The results indicate that the lifetime of LED lamps depends mostly on the stability of the driver and optical elements, rather than on the degradation of the LED chips, that have a stable output over stress time. By comparing lamps from four different manufacturers stressed at room and high temperature, we found that (i) long-Term stress causes a change of the chromatic properties of the lamps, which is ascribed to the degradation of the phosphors or to the inner LED reflector; (ii) during ageing the LED driver may degrade gradually and/or catastrophically, causing a reduction of the output optical power, or a complete failure; (iii) proper thermal management and heat dissipation reduce the degradation rate; (iv) spectral transmissivity measurements and visual inspection reveal the degradation of the diffusive optical elements, which is induced by the short wavelength side of the LED emission spectrum. © 2015 IEEE.


Trivellin N.,University of Padua | Trivellin N.,LightCube SRL | Barbisan D.,University of Padua | Barbisan D.,LightCube SRL | And 16 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2016

With this work we report on the design of an LED based star simulator. The simulator is the result of a cooperation between the Italian National Astrophysics Institute and LightCube SRL, a University of Padova (Italy) R&D spin-off. The simulator is designed to achieve a luminous output customizable both in spectrum and in intensity. The core of the system is a 25 channels independent LED illuminator specifically designed to replicate the spectral emission of the desired star. The simulated star light intensity can also be carefully tuned to achieve the correct illuminance at a specific distance from the star. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.

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