Your level of hollowing needs to be at least 15 for you to get bonus luck. Once your hollowing is 15, the number of bonus luck depends on the level of weapon. The weapon needs to be +10 to get the full 5 points. One bonus per active hand slot. Hollow shield +10 and hollow weapon +10 will give you a total of 10 extra luck. I don't know why people say this is the worst stat since resistance. You only need to level luck to 30 and have hollow LH and hollow RH to hit the 40 softcap. Plus, bleed and poison also scale with luck. A weapon doesn't lose its initial scaling when infused hollow, bleed. So, for example, a great club infused with blood has a B in str. Infused with bleed at 40 luck, it has a whopping 89 in bleed. Say hello to my little friend, demon in pain! Infused with poison, it has 117 poison! Infused hollow with 40 luck and 28 str, it still scales with luck but already has 520 AR. Arguably the best stat in the game.