• Brightness key not working Ubuntu 16.04 LTS - Exactly same problem as me, except my laptop is Lenovo IdeaPad P400 touch. Can't change brightness in Ubuntu 16.04 LTS - Tried both the solution given by @Archisman Panigrahi and by @Serge Stroobandt. Ubuntu 14.04 brightness problem (Lenovo Z500) - tried solution given by @Lorenzo Gabriele.
• Laptops and netbooks:: ideapad p series laptops:: ideapad p400 touch notebook - Lenovo Support US.

What I did was reboot and when I saw the Lenovo logo on boot up I hit the brightness key and watched the screen get brighter. When I saw that I almost had to go back to K-Mart because I could not believe how easy that was. I still don't have brightness control, but I'm no longer having to squint my eyes to look at the screen or work in the dark.

I've had my IdeaPad Notebook P500 for over a year, and rarely had an issue with it. Today, I accidently touched the F11 key, which happens to be the 'Brightness minus' key. Immediately, the screen went very dim, to the point where it actually hurts my eyes to be typing this.

I can adjust the brightness sliders up and down on the screen, using both the F11/F12 keys and the slider box available from the 'Brightness' selection under 'Settings'. Even though the sliders go up and down, the screen stays the same very dark level.

I have uninstalled and re-installed the Intel HD driver.I have shut down the laptop and turned it back on while holding the F12 (Brightness plus) button. I have even rebooted several times.

Brightness Control App

Is there a way I can get this rectified ?