This is not relevant in B/X. Neither encumbrance option involves tracking the weight of individual pieces of adventuring gear.
The only things tracked are carrying treasure vs not carrying treasure, and armor type (Basic Encumbrance) or Armor, Weapon, and treasure weights (Detailed encumbrance). In detailed encumbrance, all adventuring gear combined is treated as 80 coins of weight regardless of quantity and type.
Once a PC has completed their first expedition and has some extra coin, they should outfit themselves with a generous amount of both torches and oil flasks.