Why does my MacBook's monitor go to maximum brightness when waking up from sleep?
Try to reset the System Management Controller.

Resetting the SMC on Mac portables with a battery you can remove

Shut down the computer.
Disconnect the MagSafe power adapter from the computer, if it's connected.
Remove the battery.
Press and hold the power button for 5 seconds.
Release the power button.
Reconnect the battery and MagSafe power adapter.
Press the power button to turn on the computer.