LithLum is a legendary Runeword created by combining a Lith Rune of Ritual and a Lum Rune of Invocation.
How to Create LithLum
You can create LithLum by adding the legendary Lith Rune of Ritual and the magic Lum Rune of Invocation to a two-socketed 
Helm, 
Chest Armor, 
Pants, or 
Two-Handed Weapon.
Overflow
When LithLum overflows, you receive the Lum Rune's overflow effect (Increased Resource Restored) 4 times.
Overflow occurs when your Ritual generates more Offering than required for the Invocation. The overflow effect is proportional to the amount Offering overflows.
Legions
Helltide