The character's hand of choice is hideously scarred, and from wrist to elbow it appears as if it is a network of jagged, seemingly recently-healed wounds.
As a bonus action, you can flex the muscles of your
scarred limb causing the wounds to tear open and shed
bright light in a 20-foot radius and dim light for an
additional 20 feet for 1 hour. While shedding light, the
character’s arm is wracked with lancing pain making it
impossible to hold or manipulate objects with the injured
limb. The character must finish a short or long rest before
it can be used again.