Daz1712:
Since you have a relay operation the light already and obviously have wires run to the light, why not monitor the voltage on the output of the relay.If the light is turned on via the wall switch there will be voltage on the output of the relay event if the relay is not on, indicating that the lightswitch is on.
If the relay is turned on then there will also be voltage at the relay.
There will be no voltage only when the light is turned off.
A small "whatever voltage" plugpack that outputs 5 volts dc will then let you connect to the Arduino.
Better yet replace the light with a low voltage LED light and run the whole lot off a low voltage transformer where it will,only tingle when you grab those bare wires instead of fill the room with the sound of Sizzling Bacon!
Please Note: No matter how skilled you are it is very easy to get shocked. I speak from experience in a moment of forgetfulness and panic untill i realised the fuse had blown, not my eyes.
Daz
The arduino is the test bench for me. In the future when I will find all the code and the how to plug things correctly I am going to transfer this to a esp8266 controlled by blynk so the power for the arduino is not a problem here.
About your suggestion though I am not sure that I understand it fully. How can I monitor the output voltage of a relay? Also if I do that and I close the lights from the wall and then try and open it from the arduino nothing will happen.