Led Railway Signal vs Full Compliance with Colorimetric Specifications

In recent times, the transportation industry has generated a number of developments involving new technology in signalling. Important developments have involved the production of light by means of light-emitting diode (LED). Unfortunately, the maximum light output, dominant wavelength, reliability and the lifetime of LEDs are all closely related to the junction temperature. Accordingly, LED performance largely depends on the ambient temperature of its operating environment. Consequently, adequate heat-sinking is required to maintain a long lifetime and compliance. Today again, designing an LED railway signal that is able to meet compliance over wide range of temperatures is problematic. In particular, for yellow aspects compliance is difficult to achieve at extreme ambient temperature because the shift in the colour of yellow LEDs over the specified temperature range can be greater than the magnitude of colour specification. Use of phase change materials (PCMs) can provide practical solution of these problems. PCMs can store and release thermal energy during the process of melting and freezing (changing from one phase to another). When such a material freezes, it releases large amounts of energy in the form of latent heat of fusion or energy of crystallization. Conversely, when the material is melted, an equal amount of energy is absorbed from the environment as it changes from solid to liquid. This paper presents studies that enable the design of railway signals to meet, in a rigorous way, colorimetric compliances on a large range of temperature change. Furthermore, the proposed system is applicable, in a simple way and without operational changes, to the existing systems. It is sufficient to insert inside of the signals a suitable amount of a specific PCM.