ST Low Voltage On/Off Sensor


I’m fairly new to home automation and ST, but I’ve been able to start building a very satisfying home automation system. I am however looking for a solution to a special need I have. I have a dual energy home heating system that switches electricity billing rates based on a temp sensor in the utility meter outside. I don’t have access to this data, however, there is a witness light (LED) that goes on when in high rate mode. I would like to simply be able to flip a virtual switch (CoRE or otherwise) when the light is on. Could someone suggest a sensor or possible an existing thread to point me in the right direction. The light is probably on a less than 24v circuit.