How to adjust the brightness lenovo Z50? Can't adjust brightness lenovo Z50-70 windows 8.1 f11 f12 don't work?

How can i adjust the brightness lenovo Z50? Can't adjust brightness lenovo Z50-70 windows 8.1 f11 f12 don't work?

Read more: How to adjust the brightness lenovo Z50? Can't adjust brightness lenovo Z50-70 windows 8.1 f11 f12 don't work?