Albert Barnes Commentary Psalms 136:7

"To him that made great lights; For his lovingkindness [endureth] for ever:" — Psalms 136:7 (ASV)

To him that made great lights - (Genesis 1:14). The sun and the moon are here particularly referred to.

For his mercy ... - His mercy is manifested in all that has followed from the creation and diffusion of light—(all the beauty in the universe as seen; all the life, beauty, and vigor in the vegetable and animal world; all that there is of life and happiness in the universe—for there could be neither if darkness reigned everywhere).

His mercy is also manifested in light itself: light, the emblem of happiness; the source of joy; the producer, in large measure, of the beauties of the universe, and the revealer of those beauties everywhere.

How can a man think of light and not praise its Author?