I have a laptop ideaPad z400 from lenovo that there is a brightness trouble. When it was with windows 10. I were with the same problem, but I could fix easily installing default driver. But now, I've installed ubuntu 16.04 LTS and initially it wasn't any problem but, when I tried to change the brightness, it keep very low.
I have the same laptop and the same problem. Here is the solution I found:
You should see:
You need to adjust the first line (adjusting the second line won't do anything). Find the current brightness:
Find the maximum brightness:
Adjust it to the desired value, say 15, by:
echo 15 | sudo tee /sys/class/backlight/ideapad/brightness