Color changing light emitting diode monitoring thyristor circuit

In order to monitor the trigger conduction status of two anti-parallel thyristors or bidirectional thyristors, a
monitoring circuit as shown in Figure 13-16 can be used , and the indicator light uses a color-changing light-emitting diode .
    If the voltage output through the thyristor V is a symmetrical voltage in the positive and negative half cycles,
the red and green tube cores of the three-color light-emitting tube alternately conduct in the positive and negative half cycles, emitting
orange light. If V outputs only a positive or negative half-cycle voltage,
only one die can pass current and emit red (or green) light. Therefore , the conduction status of the thyristor
can be judged based on the color of the light .