Took me 12 days to finish this.

A complete Videowalkthrough for all 900 collectable Lightseeds:

http://www.princeofpersia-game.de/content/view/1118

Just click on the Area for which you want to know how to reach the lightseeds and watch.

The first Video for is for the 40 "normal" lightseeds and the second for the Lightseeds which need a magical power of Elika which you don't have to use to get through the area.

I think this should solve every "How to get the last lightseed in this area" question.