Light seeds appear as floating balls or energy the same colour as Elika's magical abilities and are used to help re-energize Elika after she has exorcised the Corruption from each of the fertile grounds. Elika requires the Light Seeds but the knowledge of why still eludes her other than she simply knew.
Light Seed's only appear after an area has been cleansed of corruption and 25 are awarded after each of Corrupted has been freed or destroyed. There are a total of 1001 light seeds in the entire map.
The only area not containing any Light seeds is The Temple. When the Prince Destroys the Tree and retrieves Elika's life essence it appears, similar to a Light Seed, only larger.