Inspiron 11 (3137) - Dynamic Contast

hi,

i am facing an issue in which the screen adjusts its contrast/brightness automatically

it (the whole screen display) gets dim when some dark color content is on the screen and gets brighter when some light color content on the screen.

my laptop's status;

   - adaptive brightness(window service) : off (inspiron 11 3137 doesn't have sensor)

   - display power saving technology(intel graphic driver) : off (it works on battery mode. but i'm using ac power adater)

   - brigteness doesn't change at external monitor(using hdmi).

   - brightness change at real dos.

   - bios version : a02(newest)

i don't think it's a hardware defect.

i think it's a bios level problem. but disable menu doesn't exist on bios.

please help.