[loda117]

Hi and Welcome to TSF

Let me get some things cleared to understand your issue
The screen on the monitor goes Dim? not the TV right? or both get DIM ?

 

[loda117]

If the TV screen works fine with the laptop and only the laptop screen is getting dim then that is def inverter or the backlight that are going out as makinu1der2 said

You can get the inverters now a days for fairly cheap prices online
if you feel comfortable enough to replace it yourself
does the laptop has a manual or the manufacturer's website has it ?