The opening into fullness — a flower's unfolding, and light's soft spill past its source.
Old Norse blom (flower, bloom), from Proto-Germanic *blomo, from a root meaning to thrive or flourish; the light-photography sense (a soft overflow past its source) is a modern metaphorical extension of the flower's opening.
An opening into fullness — used here for both a flower's unfolding and light's gentle overspill past its edge.