וְהָיָ֖ה בַּיּ֣וֹם הַה֑וּא לֹֽא־יִהְיֶ֣ה א֔וֹר יְקָר֖וֹת יקפאון [וְקִפָּאֽוֹן׃]
And it shall come to pass in that day, that there shall not be light, But heavy clouds and thick;
Read kabbalistic (mystical) interpretation of Zechariah 14:6: and classical mystical sources.