Light Switches in the Cellar

In your cellar there are three light switches in the OFF position. Each switch controls one of three light bulbs on floor above.
You may move any of the switches but you may only go upstairs to inspect the bulbs.
When upstairs, you cannot access the switches. What is the minimum number of times you need to go upstairs to determine the switch for each bulb?

Solution-

1. First you will turn lights switch 1 to 'ON' for few minutes and then turn 'OFF'.

2. Now turn switch 2 to 'ON'. And go upstairs.

3. There you will notice as whichever bulb is 'Off' and 'hot', that points to switch 1. the bulb which is 'ON' - is attached to switch 2. And the third bulb points to switch 3.

So we need to go upstairs only once.