وَمَا يَسْتَوِى ٱلْأَعْمَىٰ وَٱلْبَصِيرُ · وَلَا ٱلظُّلُمَٰتُ وَلَا ٱلنُّورُ · وَلَا ٱلظِّلُّ وَلَا ٱلْحَرُورُ · وَمَا يَسْتَوِى ٱلْأَحْيَآءُ وَلَا ٱلْأَمْوَٰتُ
"The blind and the seeing are not equal; nor the darknesses and the light, nor the shade and the scorching heat. Nor are the living and the dead equal."
And the last link in the series is the heaviest: the living and the dead. The ordering moves from the lighter to the heavier.
ٱلظُّلُمَٰتُ is plural, ٱلنُّورُ singular. This usage was treated in al-Baqara at 2/257, and what was recorded there can be carried over to here: darkness is the absence of light, and absence has many forms; light is one.
حَرُور — root ح-ر-ر: heat. The lexicographers generally describe ḥarūr as "the burning heat that continues through the night" or as "a hot wind", and compare it with samūm. Samūm was treated in al-Ṭūr and in al-Wāqiʿa at 56/42; I rely on that treatment.
And what is set opposite it is ẓill (shade). How shade is used in two tableaux was treated in detail in al-Wāqiʿa at 56/30 and 56/43 — there shade occurred once as mercy and once as a shelter turned inside out. Here shade stands on the good side of the contrast.
إِنَّ ٱللَّهَ يُسْمِعُ مَن يَشَآءُ وَمَآ أَنتَ بِمُسْمِعٍ مَّن فِى ٱلْقُبُورِ — "you are not one who can make those in the graves hear."
The last of the four contrasts (living/dead) turns here into a comparison. And it arrives at the same place as the question in al-Zumar at 39/19: the limit of responsibility.