SRD:Brilliant Energy

Brilliant Energy: A brilliant energy weapon has its significant portion transformed into light, although this does not modify the item’s weight. It always gives off light as a torch (20-foot radius). A brilliant energy weapon ignores nonliving matter. Armor and shield bonuses to AC (including any enhancement bonuses to that armor) do not count against it because the weapon passes through armor. (Dexterity, deflection, dodge, natural armor, and other such bonuses still apply.) A brilliant energy weapon cannot harm undead, constructs, and objects. This property can only be applied to melee weapons, thrown weapons, and ammunition.

Strong transmutation; CL 16th; Craft Magical Arms and Armor, gaseous form, continual flame; Price +4 bonus.