Jnanena Tu Tad-ajnanam

For those whose ignorance of the Self has been destroyed by knowledge, that knowledge illuminates the Supreme — just as the sun illuminates everything when it rises.

When a lamp is lit in a dark room, the darkness vanishes instantly. In the same way, when the lamp of knowledge is kindled within, the light of the Paramatma rises from inside. No external source is needed.

This shloka answers 5.15 directly. There, Krishna said beings are deluded because ignorance covers knowledge. Here, he says that when knowledge destroys that ignorance, everything becomes clear. Tradition holds the 'adityavat' simile in very high regard — knowledge, like the sun, illuminates everything at once.