Lands of Algia 4E
Elf master crafters use the leaves of the sun tree to create radiant armor of leather.
Enhancement: +2 AC
Property: Gain resist 5 radiant
Power (Daily • Radiant): Free Action. You can use this power when an enemy hits you with an opportunity attack. Deal 1d10 + Dexterity modifier radiant damage to that enemy. Published in Player’s Handbook, page(s) 231.
Found in the main chamber of the Temple of Nerilous