Hi,
Welcome to the forum.
Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html
If you have AC power lighting a 40W globe and the power fails, how do you aim to get the DC battery current to supply the AC for the Globe?
What is the mains AC voltage?
What is the battery voltage?
Can you please tell us your electronics, programming, Arduino, hardware experience?
Thanks.. Tom... 