Why is the laptop's screen to my toshiba dim and flickering?

I've had my toshiba laptop (satellite a505 s6005) for over a year and the screen got dim and flickers continuously. The screen is so dim that one can barely read or see things distinctly. The flickering is not that bad but it is more than just subtle. I understand that it can either be the back light of the screen or the inverter. Which one is more likely the culprit?