I don't have an idea on the switch with 4 pins. I understand that the switch comes with two pairs of contacts. One pair of contacts is connected to a 230V supply while the other pair of contacts is connected to a 5V supply.
The 230V supply is used to control the lamp using the NC Relay when the arduino is switched off.
When the arduino is powered on, the 5V supply reports the position of the switch to the Arduino from where the actions over the lamp are controlled.
Am I correct?