LightCube SRL

Padova, Italy

LightCube SRL

Padova, Italy
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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.


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.


Dal Lago M.,University of Padua | Meneghini M.,University of Padua | Meneghini M.,LightCube SRL | Trivellin N.,University of Padua | And 7 more authors.
Microelectronics Reliability | Year: 2013

GaN-based light-emitting diodes have recently demonstrated to be almost ideal devices for the realization of next generation light sources, thanks to their high performance and long expected lifetime. For a massive market penetration of these devices, their reliability must be significantly improved: if on one hand the physical mechanisms responsible for gradual degradation have been extensively described, on the other hand the origin of catastrophic failures still has to be investigated in detail. One of the most critical situations occurs when an LED module is directly connected to an energized power supply: this event (usually referred to as "hot-plugging") can generate current spikes up to several tens of amperes, that can potentially destroy or damage the LEDs. The aim of this work is (i) to analyze, for the first time, the nature of the current spikes generated during hot-plugging, (ii) to understand the failure mechanisms of LEDs submitted to high current spikes, and (iii) to present a simplified model to explain the hot plugging phenomenon. The study is based on transient electrical measurements, carried out on several LED modules (fabricated by different manufacturers), connected to three different power supplies. Results reveal that the amplitude and the time constants of the current spikes are directly determined by the number of LEDs connected in series and by the output capacitance of the current driver, and provide information on the gradual or catastrophic failure of LEDs submitted to current spikes. © 2013 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).


Dal Lago M.,University of Padua | Meneghini M.,University of Padua | Meneghini M.,LightCube SRL | Trivellin N.,University of Padua | And 7 more authors.
Microelectronics Reliability | Year: 2012

The aim of this work is to investigate the thermal stability of remote phosphor plates to be used in solid-state lighting systems, for the conversion of the blue light emitted by GaN-based LEDs into white light. A preliminary thermal characterization revealed that in normal conditions of blue light irradiance the phosphor plates can reach temperature levels higher than 60 °C, which can affect both performance and reliability. The results of accelerated thermal stress tests indicate that high temperature levels can trigger a relevant degradation mechanism (estimated activation energy is 1.2 eV), that drastically reduces the phosphor conversion efficiency and modifies the photometric and colorimetric characteristics of the emitted white light. © 2012 Elsevier Ltd. All rights reserved.


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.


Dal Lago M.,University of Padua | Meneghini M.,University of Padua | Meneghini M.,LightCube SRL | De Santi C.,University of Padua | And 7 more authors.
Microelectronics Reliability | Year: 2014

This work presents an extensive study on the effects of Electrostatic Discharges (ESD) on state-of-the-art GaN based LEDs, based on optical and electrical measurements carried out during the ESD events. ESD events were simulated through a Transmission Line Pulser (TLP) which generates voltage pulses with a duration of 100 ns and increasing amplitude: during each pulse, spatially-resolved electroluminescence measurements were carried out through an high speed EMCCD camera. These measurements allowed to identify the chip region where the discharge is localized and the change in the damaged area induced by consecutive ESD events. Also the current and voltage waveforms at the LED terminal were monitored during the tests; this analysis provided important information about modifications the impedance of the devices. The analysis was carried out on different types of commercially available low-power GaN-based LEDs with several differences in the manufacturing technology. Thanks to these tests we have identified two different failure behaviours during a destructive ESD event, clearly related to the different defects in the semiconductor lattice and to structure of the chip. © 2014 Elsevier Ltd. All rights reserved.


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.


Patent
Lightcube S.r.l. | Date: 2014-07-23

The present invention refers to a LED lighting module that comprises a primary chain of LED devices and secondary chains of LED devices. The primary chain of LED devices is connected in series to a current generator, adapted to provide a supply current to the lighting module. The secondary chains of LED devices are connected in parallel to one another and in series to said current generator and to said primary chains of LED devices. The primary chain and one the first and second secondary chains form different lighting units with different colour temperatures. The lighting module comprises one or more electronic switches, through which it is possible to alternatively turn on/off one of the lighting units in order to change the colour temperature of the light emitted by the lighting module.

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