The following is taken from Exodus chapter 10:21-23, "Then the LORD said to Moses, "Stretch out your hand toward heaven that there may be darkness over the land of Egypt, a darkness to be felt." So Moses stretched out his hand toward heaven, and there was thick darkness in all the land of Egypt three days; they did not see one another, nor did any rise from his place for three days; but all the people of Israel had light where they dwelt."
Is there anything that we can glean from this? Notice that darkness was to be felt? I've been in the desert where there were no street lights, no traffic, a place where you could not see your hand a foot from your face, but I never felt that kind of darkness. Also notice that the duration was three days. That has a numerical value attached to it, Jesus was in the tomb for three days as an example. The darkness was so "thick" the Egyptians could not move about under normal circumstances. Everything shut down, yet the people "of Israel had light where they dwelt".