Light

Light is a metaphor for Creation, which began some time after the
beginning of the story.  The continual breaking forth of light suggests
that Creation is not a single event but a process that goes on until the end
of Time.
Eternity is Light; mortal life is darkness (Ulro)

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The word light appears 174 times in Poetry and Prose of William Blake.

From Thel:

For thou shalt be clothed in light, and fed with morning manna:

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From The Little Black Boy:

Look on the rising sun: there God does live
And gives his light, and gives his heat away.      
And flowers and trees and beasts and men recieve
Comfort in morning joy in the noon day.

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The Book of Los refers to the Blakean Creation (when Light began):

Chap: IV:   
I: Then Light first began; from the fires             
Beams, conducted by fluid so pure .
Flow'd around the Immense:

PLATE 54 of of Jerusalem (Erdman 203)
In Great Eternity, every particular Form gives forth or Emanates
Its own peculiar Light, & the Form is the Divine Vision
And the Light is his Garment

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The Four Zoas: the end of the 5th Night (Erdman 344):
I well remember for I heard the mild & holy voice
Saying O light spring up & shine & I sprang up from the deep    
He gave to me a silver scepter & crownd me with a golden crown