Light is sown — i.e., scattered. The metaphor must not be pressed so as to think of a harvest to come. The image is an obvious and common one.
“Sol etiam summo de vertice dissipat omnes
Ardorem in partes, et lumine consent arva.”
LUCRETIUS.
And Milton, while enriching its metaphor, doubless had the psalm in his mind: —
“Now morn, her rosy steps in the Eastern clime
Advancing, sow’d the earth with orient pearl.”