The lights

First, switch on a light for 5 minutes (call this switch A), then turn off and turn another one on (assume this is switch B) and check.

The one is lighting is connected to switch B.

The one isn't lighting but hot is connected to switch A.

The other one is connected to the only left switch.

Let the switches be A, B and C.

Turn on Switch A. Keep it on for 5 minutes.

Now, Turn switch A Off, And turn On Switch B.

Now, Go up the staircase. The Light Which is Glowing Is connected to Switch B. Then, Touch the two remaining lights with your hand. The one which is Hot, Is connected to Switch A because it had been on For some time.. The last bulb is connected to switch C.

Thus, We need a minimum of 1 trip to figure out Which light bulb is connected to which switch.

Cheers!

Turn two lights on, turn on of those off.

One will be on, one will be warm, one will be off.

Well if I were any of you all I would have done it by the concept of electric current heat supply h= I^2RT hence h is directly proportional to t that is temperature and h is heat supplied so the more the time the switch is on more will be the heat radiated hence this problem is solved

You can figure out which switch works each light in one trip only if no bulbs are burnt out and all switches are wired so the circuits are open or closed when each switch is in the same position.

$\text{Light becomes hot when blowing.}\\ \text{So put on the first switch for 10 minutes or so. then put on the second.}\\ \text{Now go and check upstairs.}\\ \text{The hot one belongs to first switch, the blowing one to second and the cool not glowing one to the third.}$