(Isra) 17 : 12
وَجَعَلْنَا اللَّيْلَ وَالنَّهَارَ آيَتَيْنِ ۖ فَمَحَوْنَا آيَةَ اللَّيْلِ وَجَعَلْنَا آيَةَ النَّهَارِ مُبْصِرَةً لِتَبْتَغُوا فَضْلًا مِنْ رَبِّكُمْ وَلِتَعْلَمُوا عَدَدَ السِّنِينَ وَالْحِسَابَ ۚ وَكُلَّ شَيْءٍ فَصَّلْنَاهُ تَفْصِيلًا
And We have made the night and day as two Signs, and We have made obscured the sign of the night and made the sightful the sign of the day so that you may seek the Bounty from your Lord and may know the number of years and calculate. And We have explained everything in detail.
The Three-Time-Knower Lord has arranged the day for livelihood and the night for resting as told in verse 78: 10-11. And It is told in verse 78: 19 that, Lord has made the sun as the burning lamp. See explanation 3: 190-194; 7: 52 and 16: 89.