On what day did God create light?

Day One, my friend. Light was the first thing created. This is how it goes in Genesis 1:1-3 ;

'In the beginning God created the heaven and the earth. And the earth was without formform and void; and the darkness was upon the face of the deep. And the Spirit of God moned upon the face of the waters. And God said, "Let there be light:"and there was light.'