Brightness Issue in my Hp 15-R006TU Note book

Hi,

I have a problem with my screens brightness.Its My HP 15-R006TU notebook.I purchased my notebook on may 31 and it came with DOS OS.So i formatted it windows7 64 bit OS.But now i am having some display problem.When i am switching over any window my brightness incresing slowly and again if i will move to any dark screen then it change slowly. When i connect charger it goes asusal.

for e.g:

Let us consider i am watching a video in some player.suddenly if i will move to my desktop screen the light will change slowly either increase (If bright)/dim slowly.This made me sad after purchased my new HP notebook :(

Kindly help me or suggest me what to do.

Regards,

Asish Kumar Panda