Kommentar zu Bereschit 6:16

צהר A LIGHT — Some say this was a window; others say that it was a precious stone that gave light to them (Genesis Rabbah 31:11).

בצדה תשים, on the side which is wide, for that is the side called צד. The long side is referred to as צלע.

צהר, this word is derived from the word צהרים, “noon,” an instruction that Noach make a window in the ark that would let in the light after the rain would stop falling, during the long period when the water level would gradually subside. This is what is meant in 8,7 when the Torah wrote ויפתח נח את החלון, “Noach opened the window.” Some of our sages (Bereshit Rabbah 31,11 ) believe that Noach suspended a brilliant gemstone which provided light inside the ark. The words תעשה לתבה, “you shall construct for or inside the ark,” contradict such an explanation. There is no question that Noach had prepared oil for the lamps he took along into the ark. The window mentioned here in our verse is a natural source of light, affixed by Noach in the highest part of the ark.