Tanach zu Schemot 7:25

Adonoy said to Moshe, “Stretch out your hand toward the sky, and there will be darkness over the land of Egypt. The darkness will be tangible.”

Moshe stretched out his hand toward the sky, and there was total darkness in the entire land of Egypt for three days.

Man could not see his fellow man, nor could anyone rise from his place for three days. But all the B’nei Yisrael had light in their dwellings.