I have a W500 (type 4061) on which I'm having troubles with the brightness controls.
After initial startup, I'm able to use Fn+Home and Fn+End to control the brightness. The brightness OSD shows the brightness level as it is being adjusted.
But, occasionally (maybe 25% of the time???), the brightness keys do not work after putting the computer to sleep and waking it up. When this happens, I am able to use the other Fn keys (for example the LED light/PgUp key). It is only the brightness that I've noticed stops working. In addition, the "mobility center" (Win+X), no longer contains the brightness widget.
I've not found any cause as to why brightness controls work sometimes but not other times.
I've set the laptop to use the integrated (Intel) graphics and disable the OS auto-detection of switchable adapters.
I have run the Lenovo update program and believe that all of my software is up to date.