The lyrics to this hymn are by Charles Wesley, the same guy that gave us "Hark the Herald Angels Sing." I's set to a Welsh tune called Hyfrydol, which looks like it's pronounced like the sound an old man makes when he coughs. Wesley only wrote two verses, which is not enough, so I added one more, the one that says:
"When the world was steeped in darkness
When the world had lost its way
No hope in sight
No breath of light
You broke forth like break of day."