Yunus 10:67
The verse's two verbs assign different purposes to night and day.
هُوَ ٱلَّذِى جَعَلَ لَكُمُ ٱلَّيْلَ لِتَسْكُنُوا۟ فِيهِ وَٱلنَّهَارَ مُبْصِرًا ۚ إِنَّ فِى ذَٰلِكَ لَـَٔايَـٰتٍ لِّقَوْمٍ يَسْمَعُونَ
It is He who made the night for your rest, and the daylight for visibility. Surely in that are signs for people who listen
Yunus 10:67 · Translation: talal-itani
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"Li-taskunū" — that you may find stillness; the root "sakana" means "to halt, to settle, to rest." Night is a time for stopping. Day, by contrast, is "mubṣir" — illuminating, giving sight to the eye. Two spans of time are bound to two distinct human needs: for one, to rest; for the other, to see. The verse does not merely call night "the dark time" and day "the bright time"; each has its own function.
Observation
Chronobiology shows that the body carries a roughly 24-hour internal clock — the circadian rhythm. The hormone melatonin rises with evening darkness, sleep pressure climbs, body temperature falls, metabolism slows. By day the reverse: cortisol rises, alertness increases, digestion quickens. The verse's pairing of "night for stillness, day for seeing" can be set alongside this internal rhythm: the kind of need that takes refuge in the night has a counterpart in modern physiology.
Exegesis
Al-Qurṭubī dwells on the phrase "li-taskunū" — stillness is not merely sleep but the resting, together, of mind, body, and the senses. The verse also hints at the proper time for contemplation; classical exegetes see the last third of the night (the hour of tahajjud) as contemplation's clearest moment. The closing of the verse is telling: "for a people who hear." Night is not made for seeing — it is made for hearing.
Sources
Tafsīr: Abū ʿAbdillāh al-Qurṭubī, al-Jāmiʿ li-Aḥkām al-Qur'ān. Science: chronobiology — circadian rhythm, melatonin regulation (basic physiology).