I had this same issue. White screen, chime, responded to light sensor. Hooked to external monitor, would get video there. But I could only get a white screen on the internal monitor. I swapped the logic board with a known good logic board and this fixed the issue. So I'm going to say it's a logic board issue, strange as it is, or a logic board to LVDS connector issue (all I did was remove this, the HDD connector, data/usb connector, airport card connector, magsafe port, iSight connector(?), and top case connector, to swap the logic board). I had a !@#$ of a time finding any info, so I hope this helps some people out there. I'm going to investigate and see if I can find any further answer to this.