How do I turn the lamps/lights off/on?

See the answer to Why my lights don't work for details about when the lamps/lights should turn on.

If you're lamp won't turn off, it may be because of the way that the feature works. For example, you may have a lamp on to indicate that you have joined a call group. Pressing the key will not immediately turn the lamp off - you will first be asked to confirm that you want to leave the group. When you press the softkey associated with Yes, the lamp for the group key will be turned off.