Minecraft wiki entry for Respawn_Anchor, associated text: When crafted, a respawn anchor has no (zero) charge and can't yet be used until charged. When a glowstone block (not glowstone dust) is used with it, a charge is added, the texture of the block changes, and it starts emitting a light level of 3. Up to four glowstone blocks can be used to charge the anchor. The charge is indicated by a dial on the side of the block. Each additional piece of glowstone after the first increases the light level by four, up to a maximum of 15.