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