MacBook Pro screen dimming problems after EFI 2.3 update
This is what I did and it worked for me:


  1.Shut down the computer.
  
  2.Plug in the MagSafe power adapter to a power source, connecting it to the Mac if >its not already connected.
  
  3.On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time.
  
  4.Release all the keys and the power button at the same time.
  
  5.Press the power button to turn on the computer. 
  
  Note: The LED on the MagSafe power adapter may change states or temporarily turn off when you reset the SMC.