Contradiction with Revelation 21:23
This verse describes the city having no need for the sun or moon because the glory of God did light it, contradicting the notion in Zechariah 14:6 of there being a unique day without light.
Revelation 21:23: And the city had no need of the sun, neither of the moon, to shine in it: for the glory of God did lighten it, and the Lamb [is] the light thereof.
Contradiction with Genesis 1:3
This verse speaks of God creating light, which contrasts with Zechariah 14:6's concept of a day that is not known to be day or night.
Genesis 1:3: And God said, Let there be light: and there was light.
Contradiction with Isaiah 60:19
This verse claims the Lord will be an everlasting light instead of the sun, which contrasts with the unique day of neither clear nor dark mentioned in Zechariah 14:6.
Isaiah 60:19: The sun shall be no more thy light by day; neither for brightness shall the moon give light unto thee: but the LORD shall be unto thee an everlasting light, and thy God thy glory.
Contradiction with Revelation 22:5
This verse speaks of eternal light with no night, differing from the unique day without light and darkness in Zechariah 14:6.
Revelation 22:5: And there shall be no night there; and they need no candle, neither light of the sun; for the Lord God giveth them light: and they shall reign for ever and ever.