Because God is light.
"This then is the message which we have heard of him, and declare unto you, that God is light, and in him is no darkness at all."
-- 1 John 1:5
"Unresting, unhasting, and silent as light,
Nor wanting, nor wasting, thou rulest in might;
Thy justice like mountains high soaring above
Thy clouds which are fountains of goodness and love."
-- "Immortal, Invisible, God Only Wise", Walter Chalmers Smith, stanza two (1867)
