Sounds like your display is dimming due to settings under power options, so go to control panel,power options, select your highlighted power plan, then advance settings, look for display in list click and adjust to fix. It usually more than one option.
Although your Lenovo might have its own power management software if so check its settings.
I can't do Options 1 and 2 for some reason. Under PC and devices>Power and sleep, I don't have an option for auto brightness. Only an option to change the time the display stays on. Same issue with the Intel graphics card setting...I don't have the power saving option. :-(