If it is very dim, it may be the backlight (part of the LCD) or the inverter dying. I am not so sure about compatibility of inverters (esp. with your brand of LCD assembly), but I think they should be the same/similar/compatible because we are talking of the one model of laptop alone.
One test I have in mind is to put back the old LCD. Yes, distortions on the screen display may be present as it is the original problem but may be the brightness of the screen will give you an idea if it is the inverter (this is assuming the old LCD has good backlight).