can someone help me to obtain the source of light
If you kept the Lake of the Lizards Pure:
continuously enter and exit the Lake of Purity. It will get you Glowshrooms at random
then seek out Othra or the Witch and they can help you from there.
Just equip the amulet and your good to go.
If you corrupted the Lake:
Go to the Trolls Bridge and seek out for a alternative path
It will lead you to a cave where you find Glowshrooms
Then go to the Witch.