The city does not need the sun or the moon to shine on it, for the glory of God gives it light, and the Lamb is its lamp. The nations will walk by its light, and the kings of the earth will bring their splendor into it. On no day will its gates ever be shut, for there will be no night there.
Revelation 21:23-25

Many people perceive this as a heaven which is in the future.

There will be no more night. They will not need the light of a lamp or the light of the sun, for the Lord God will give them light. And they will reign for ever and ever.
Revelation 22:5

Let’s look at this shall we?

the people living in darkness
have seen a great light;
on those living in the land of the shadow of death
a light has dawned.”
Matthew 4:16

In him was life, and that life was the light of all mankind.
John 1:4

When Jesus spoke again to the people, he said,

I am the light of the world. Whoever follows me will never walk in darkness, but will have the light of life.
John 8:12

I have come into the world as a light, so that no one who believes in me should stay in darkness.
John 12:46

You are all children of the light and children of the day. We do not belong to the night or to the darkness.
1 Thessalonians 5:5

but it has now been revealed through the appearing of our Savior, Christ Jesus, who has destroyed death and has brought life and immortality to light through the gospel.
2 Timothy 1:10

But you are a chosen people, a royal priesthood, a holy nation, God’s special possession, that you may declare the praises of him who called you out of darkness into his wonderful light.
1 Peter 2:9

Don’t we realize Revelation 21 and 22 are actually a fulfillment of this?

The sun will no more be your light by day,
nor will the brightness of the moon shine on you,
for the Lord will be your everlasting light,
and your God will be your glory.
Your sun will never set again,
and your moon will wane no more;
the Lord will be your everlasting light,
and your days of sorrow will end.
Isaiah 60:19-20

The Lord is already my light. This is because the veil of darkness has been removed from me.

And we all, who with unveiled faces contemplate the Lord’s glory, are being transformed into his image with ever-increasing glory, which comes from the Lord, who is the Spirit.
2 Corinthians 3:18

It’s already happened. You are all children of that city. The New Jerusalem.
The light of all men lives inside you.

The true light that gives light to everyone was coming into the world.
John 1:9
~ Simon Yap