Night and Day

[Owl]

To me, the title is too cliche and uncomfortably explicit, though you do have some really great lines scattered throughout the poem, so don't be discouraged at all! I think if you thought through the title a bit more, you'd come up with a much more interesting (keep it relevant!) set of words to label your poem with.
Also, I don't know much about meter at all, but since you're rhyming here, I think (if you haven't already) you should look into how that is crucial to this sort of poem to be sure that you're applying it correctly.

You are the day.
I am the night.
You are the light.
I am the dark. I'll just start here: L1-L4 are far too overused. I've heard those phrases before-- though, I bet that you could conjure up a really amazing/original way of restating those ideas, including words dense with meaning. In the process, you could probably cut them down successfully into 2 lines instead of 4.
But in your sights all flames are dull, A non plural form of "sight" seems more appropriate here, I'm a bit unsure though.
and embers embrace a stiller soul.
You shine so bright it's hard to bare, This line definitely needs more imagination integrated within it, otherwise it'll border on being awkwardly cliche (which also hinders this line's effectiveness).
so I offer you my cloak to wear.
For my embrace on either side,
gives mortal eyes a place to hide.
The fairest face has power more
than earthly creatures can endure.
And what a pity it would find
to, by your brilliance, turn them blind. The cutoff that "by your brilliance" is too stiff and seems to throw me off when I'm reading through the line.
The world of light can now be shown,
because my shadow has been thrown.
You are the day.
I am the night. This line, and the one prior, seem to need revision because they have the same issues that L1-L4 have.
And by my darkness,
light is known.