Back - light problem. Check and replace damaged component/s at its back-light inverter
board, or replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. It will be best to replace the inverter board as card basis.
In some models of LCD TVS; the backlight inverter and its T'Con board will be a part of the panel itself, and will be a built-in type inside the LCD panel. If so, they can't be replaced. In this case; a panel replacement is the only repair. For some other models, the backlight inverter section circuit will be a part of the main power supply regulator [SMPS]. To such sets, the power supply section circuit too should trouble shoot. Contact any service technician. The circuit will differ with models and versions.
Just understand; usually circuit diagram to Philips brand devices will be much complicated than other brand devices. So; you should have skill to locate the faulty section circuit.
I advice you to contact any service technician; or the authorized service center for Philips in this case. Surely you will feel some difficult to go with this set's repair.
Type in the brand name and type of your device, in the search box [at the top right
] of the display window; to gather down all the posts related to your device brand. It will make surf easy.