Ambient light sensor for automatic backlight adjustment?

This really does need to be implemented in a smartphone, just so I can laugh about it.

Patent the idea, quick.
hasn't this been already implemented ? Afaik my Samsung Note 3 uses the camera for automatic backlight dimming, and it also detects wether you still look at the screen or not and triggers the lockscreen timer accordingly
I was talking about using biometrics for backlight brightness adjustment.  I didn't know it was used for locking the screen, which is pretty cool.