“Make a tzohar for the ark…” (Genesis 6:16).
Rashi* cites two views regarding what the tzohar was. One understanding is that it was a window that functioned as a skylight for the ark. The other view is that it was a luminous stone.
Previously, Rashi presented two views of what was meant by the qualifier when the Torah said (Genesis 6:9) that Noach was righteous “in his generation.” One was that this showed how truly righteous Noach was, since he wasn’t dragged down by his wicked generation. The other view was that he was only righteous compared to his wicked generation. Had he lived in Abraham’s generation he wouldn’t have shone.
When Lot and his family later fled the destruction of Sodom, they were told not to look back (19:17). Rashi explains that they were only being saved through the merit of Abraham and they had no right to watch the city being destroyed and gloat.
With this idea, we can see that the views of Rashi about the light source in the ark are consistent with his perspectives on the righteousness of Noach. According to the view that Noach was truly righteous, the light source could be a window through which he could look out at the destruction of the flood. But according to the view that he wasn’t truly righteous, the light source for the ark would have to be a luminescent stone that would prevent him from seeing the destruction outside. (Pardes Yosef)
* Rashi is the acronym of Rabbi Shlomo Yitzchaki, famous 11th century French Torah commentator