Horn of Light is a Equip Spell Card.
Spell Cards are usually activated from the hand on your turn unless their type gives another timing window.
On the current TCG and OCG Forbidden & Limited lists tracked here, Horn of Light is Unlimited.
YGOPRODeck lists Horn of Light for these formats: GOAT, OCG GOAT, Duel Links, Common Charity, Edison, TCG, OCG, Master Duel.
A listed print of Horn of Light appears in Dark Beginning 1 (DB1-EN004) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for Horn of Light is about $0.05 on Cardmarket (prices change frequently).
