Macbook turns on with light

You have two light sensitive sensors on the computer. The camera, which if a camera software is running such as iChat or Photobooth, may trigger the machine to think it is about to get some input, however I don't know where the setting for that would be. The other is the one for the keyboard. The one for the keyboard is under the speaker grills that are either side of the keyboard. If you can duplicate the experiment simply by putting your hands over the speaker grills immediately after putting it to sleep, and then removing your hands when there is light in the room, you know it is those sensors that for some reason are being activated.

My advice - get rid of this lamp immediately!
Just a guess, is it a fluorescent, balanced lamp? One of those with a "brick" balance on the cable or a balance built into the globe itself?
A low voltage halogen with a transformer?
If so, I can tell you that a while ago, one of them have fried my motherboard on an old PC.
Obviously the amount of electromagnetic pulse is out of control and sends random currents through anything electrical around it.
Better safe than having a "funny story" to tell. Stop experimenting, get rid of the lamp.

cheers

If that's the case, then we'd see a lot more reports of this. Halogen lamps are much more common as desk lamps these days. It would suggest the magnetic shielding around the power supply isn't sufficient. At very least have the power supply investigated by an authorized service center if nothing is reported wrong by the hardware test that came with the machine, and explain to them why you think it might be a problem.

It did happen to me, two short beeps, new motherboard.
I'd suggest the lamp is moved away, just in case...

So, the plot thickens...
Does it happen when the computer is unplugged and running off a battery?
As you say, it could be the wiring of your place, who knows...

That sounds like the wake from sleep settings. Check your System Preferences.