This is a sign that the backlight that lights up the screen is going out. You'll need to buy new backlight and install it yourself (which requires taking the laptop apart) or pay someone qualified to do it for you.
The information on Computing.Net is the opinions of its users. Such
opinions may not be accurate and they are to be used at your own risk.
Computing.Net cannot verify the validity of the statements made on this
site. Computing.Net and Compnet Ventures, LLC hereby disclaim all responsibility
and liability for the content of Computing.Net and its accuracy.