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.
SCHIRRIPA SPAGNOLO, G., Donato Papalillo, D., Martocchia, A. (2012). Light emitting diode in stationary transportation applications: wavelength response to varying temperature. In Materials, Devices, and Applications for Solid State Lighting XVI (pp.82781P1-82781P8). Bellingham, WA : SPIE [10.1117/12.909490].
Light emitting diode in stationary transportation applications: wavelength response to varying temperature
SCHIRRIPA SPAGNOLO, Giuseppe;
2012-01-01
Abstract
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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
