I really like floating things in a design and I couldn't miss this opportunity. Because this is a bow of a celestial ranger, you can even see the tiny diamonds shapes that indicates the Aureliate gods. In designing weapon properties, I wanted to give Rangers a similar damage versatility as Paladin's smites, so this works. The difference here is that the spell slot is expended before an attack that may miss, but damage is higher.
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Enchanted by celestials for the Dawn Seeker rangers that glide among them, this weapon has seen countless righteous battles and betrayals. It has served as symbols of hope in the past, its arrival heralded by a blazing arrow arcing over a battlefield. Even normally, each arrow fired from this weapon leaves a brief trail of softly glimmering sparks.
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Daybreak
Weapon (longbow), rare (requires attunement by a Ranger of 3rd-level or higher)
Ammunition fired from this magic bow counts as magical for purposes of overcoming resistance or immunity to nonmagical attacks and damage.
Natural Light. While attuned to this bow, you can cast the light cantrip from the bow. Immediately before you fire a piece of ammunition from the bow, you can also cast light on the piece of ammunition (no action required).
Dawn Smite. Immediately before you make a ranged attack roll with this weapon, you can expend one of your spell slots to infuse the fired ammunition with primal light (no action required). You deal extra radiant damage to a target you hit or half as much radiant damage to a target you miss. The extra damage is 2d10 for a 1st-level spell slot, plus 1d10 for each spell level higher than 1st, to a maximum of 5d10. If your target is a plant, any extra damage it takes is halved.