Albert Barnes on Revelation 21:23

And the city had no need of the sun, neither of the moon, to shine in it. This imagery seems to be derived from Isa 60:19-20. Isa 60:19 Isa 60:20. No language could give a more striking or beautiful representation of the heavenly state than that which is here employed.

For the glory of God did lighten it. By the visible splendour of his glory. Rev 21:11. That supplied the place of the sun and the moon.

And the Lamb is the light thereof. The Son of God; the Messiah. Rev 5:6; Isa 60:19.

(a) "sun" Rev 22:5, Isa 60:19,20 (b) "the light" Jn 1:4