DELL VOSTRO auto contrast/brightness changes.

I purchased VOSTRO 5402 Laptop recently. 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..THIS iS SO ANNOYING and affect my eyes... According to my experience searching on internet I am not the only one who faced this kind of Issue Dell forum is filled with such issues and no proper solution for this problem is found yet.

Issue Examples: Scrolling down a website that has light content at the top and dark content at the bottom.. so while scrolling the brightness changes for the whole screen and it is legible.

switching between two different windows or two different tabs that has different color shades (light and dark e.g light blue to dark brown or vice versa) the screen seems to change its brightness according to the color's density.

This issue occurs only when laptop is on Battery mode and not on Plugged in Mode, May be there is some setting that has to be ticked off or some software that has to be uninstall which is unknown yet.

I have done almost all the possible tricks that I could find on internet through Dell and other forums.. PLS SUPPORT ASAP