'Darkness' in the Bible

Then I saw that wisdom excelleth folly, as far as light excelleth darkness.

The wise man's eyes are in his head, and the fool walketh in darkness: and yet I perceived that one event happeneth to them all.

All his days also he eateth in darkness, and he is sore vexed, and hath sickness and wrath.

for it cometh in vanity, and departeth in darkness, and the name thereof is covered with darkness;

Yea, if a man live many years, let him rejoice in them all; but let him remember the days of darkness, for they shall be many. All that cometh is vanity.