Use of inherent physical properties of LED for their safe monitoring in railway signaling

This paper proposes a method for monitoring proper function of light emitting diodes (LED) in railway optical signals, based on some inherent physical properties of this diodes and also on some physical properties of the optical system of the signal lamp. A partial reflection of light on optical interfaces in front of LED chip is used to evaluate the irradiated power of lighting LED. Switching two or more diodes enables to use their photoelectric properties as a photodetecting element. A simple relaxation oscillator, which uses internal capacity of LED´s p-n junction is proposed as a simple analog interface to an MCU, which drives or monitors the lamp and sends the information on its state to the upper level interlocking system.