Strong Light Runes need a Starstone along with a Blank Rune; a Silver Ingot and three Normal Light Runes to make one Strong Light Rune.
Strong Runes can be crafted at level twenty at the Rune Altar.
You need three of these to learn Cleansing Light and you will need extra to cast the spell.
The command to make a Strong Light Rune is [nya!rpg rune altar strong light]. For more info use [nya!info strong light rune].