ambient light

ambient light control.
when waking up control does not work till f1 or f2 is pressed
why???

 

ambient light on mac pro

seems when the computer "wakes up" the ambient light control does not function until i use the f1 or f2 key. increasing the light using these keys then seems to initiate the ambient light control function.
this does not seem to be constant however.
before putting the computer to sleep all is well - it is only after a period of inactivity that this particular function does not operate until going thru the above procedure (f1/f2).
when the f1/f2 are pressed, i notice that the "light reading icon" always shows zero and the screen goes blank until repeated pressings of the buttons.
strange - this morning the computer woke up and everything worked fine.
thanks for your interest!