The 'shadows' are cast by the Light, certainly, but it is the material world which causes the shadows. My feeling now is that light shining in/through branches/hair is perhaps a 'foreshadowing'
of that future world, Arda Remade, when things will shine with spiritual light of themselves. It is an image at once of what
was (or at least of what was
intended & of what
will be. In a way it is a 'glimpse' beyond the Circles of the World (beyond time & space). The 'visions' of light in branches & hair are mystical experiences, glimpses of the divine in the mundane.
'O light to us that wander here, amid the world of woven trees' speaks of the Elves longing for what they cannot have. The Elves cannot leave the world of woven trees, because they are bound within the circles of the world. For mortals the Elves themselves provide a glimpse of Divine beauty, yet the Elves themselves will never know that divine beauty till Arda is remade, whereas Men will encounter it when they die. The Elves are carriers of an 'image' of something they cannot themselves know or experience.
I think this perhaps accounts for Men's restlessness - it is part of the Gift of Eru that Men will find no rest in the World - even when they achieve their desires they are not satisfied - they simply desire something else. Their 'freedom' to act beyond the constraints set by the Music is both driven & limited by their insatiable desire. In Middle-earth, at least, Men cannot love the Earth for its own sake (as Finrod comments in the Athrabeth) as the Elves do, because Eru has set this 'desire' in them. Men are driven, & destined never to be satisfied by what they have.
Or something like that.....