Why certain items with ‘light’ hurt vampires and some – not?
Light damage rules are complex, some items have fiery light, some have magical light. the fiery light will never hurt undead/demons, the other can, depending on light intensity and other stats of the item, for example BLESSED or if the item has inherent SLAY_UNDEAD flags etc… Maybe fiery light can also hurt if item is SLAY_UNDEAD or similar