The Quran

هُوَ الَّذي جَعَلَ الشَّمسَ ضِياءً وَالقَمَرَ نورًا وَقَدَّرَهُ مَنازِلَ لِتَعلَموا عَدَدَ السِّنينَ وَالحِسابَ ۚ ما خَلَقَ اللَّهُ ذٰلِكَ إِلّا بِالحَقِّ ۚ يُفَصِّلُ الآياتِ لِقَومٍ يَعلَمونَ

Muhammad Asad

He it is who has made the sun a [source of] radiant light and the moon a light [reflected],¹ and hasdetermined for it phases so that you might know how to compute the years and to measure [time]. None of this has God created without [an inner] truth.² Clearly does He spell out these messages unto people of [innate] knowledge:

The nouns diya' and nur are often interchangeable, inasmuch as both denote "light"; but many philologists are of the opinion that the term diya' (or daw') has a more intensive connotation, and is used to describe "a light which subsists by itself, as that of the sun and fire" - that is, a source of light - while nur signifies "a light that subsists by some other thing" (Lane V, 1809, on the authority of Taj al-'Arus ): in other words, light due to an extraneous source or - as in the case of the moon - reflected light.
Lit., "God has not created this otherwise than in accordance with truth" - i.e., to fulfil a definite purpose in consonance with His planning wisdom (Zamakhshari, Baghawi, Razi): implying that everything in the universe - whether existent or potential, concrete or abstract - is meaningful, and nothing is "accidental". Cf. 3:191 - "O our Sustainer! Thou has not created [aught of] this without meaning and purpose (batilan)"; and 38:27 - "We have not created heaven and earth and all that is between them without meaning and purpose, as is the surmise (zann) of those who are bent on denying the truth".