6 February 2012 Light emitting diode in stationary transportation applications: wavelength response to varying temperature
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In recent times, the transportation industry has generated a number of developments involving new technology in signaling. Important developments have involved the production of light by means of light emitting diode (LED). The optical proprieties of LEDs depended on junction temperature. Since the heat from the junction must be dissipated into the ambient somehow, changing the ambient temperature affects the junction temperature and hence the emitted light. When the LEDs have been used in the railway or traffic signals, the optical proprieties of these have to maintain more rigorous color specifications. Besides, the limits imposed must be respected in ample range of variation of the ambient temperature (typ. 233-347K). The peak wavelength of LED shifts proportionally to changes in junction temperature. Therefore, to respect color specifications with signals using LED as light source it is not simple. In this paper, we describe problems of the temperature dependent changes of colorimetrical parameters of LEDs. Besides we will introduce a method through which to build a correct signal with feedback that, according to the measured temperature, it reacts to correct the optic characteristics of signal.
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Giuseppe Schirripa Spagnolo, Giuseppe Schirripa Spagnolo, Donato Papalillo, Donato Papalillo, Andrea Martocchia, Andrea Martocchia, "Light emitting diode in stationary transportation applications: wavelength response to varying temperature", Proc. SPIE 8278, Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVI, 82781P (6 February 2012); doi: 10.1117/12.909490; https://doi.org/10.1117/12.909490


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