I'm Working for Home Automation system through raspberry pi, I'm turn on/off lights and A/C through Raspberry pi(build application of web, to control lights/AC) either case AC switched on with physcical switch board, i need to update this value to web interface so that i know that AC is power on through swich board. How it possible to read state of the AC.
Your "physical switch board" would need some indicator of the power state of the relay or switch that's readable via a low-voltage system. Assuming that's available, you'd read that via a second GPIO pin to keep the current status independent of what signals you've sent via the control pin.
In similar projects, I check the GPIO value of that pin.
In my case, the relays are active when it's low, so a 0 value means it's on.
If you're looking to -double check- the value, then have you considered photo-diodes or similar light sensors?