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.
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). 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 specifications. The junction temperature of the power LEDs affects the device's luminous flux of the device. In this paper, we describe problems of the temperature dependent changes of LED intensity. Besides we will introduce an innovative technical to allow the use of the LEDs in applications with rigorous specifications.
At present, the progress in optics is associated with wide use of diffractive optical elements (DOEs). In this paper we present a DOE design method, which not use computer iterative methods. Starting from the knowledge of the expression of the propagated field on image plane, we use simple formulas to obtain the entire information necessary to characterize the desired DOE. The DOE designed with the proposed method can equate an arbitrary complex amplitude transmission T(r) and has higher imaging accuracy than other DOEs. Even if it is possible studying any level combination, the aim of this paper is to summarize the results of simulation experiments which were carried out only to test the binary level diffractive optical elements (DOEs).
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