If the sun was not created until the fourth day, how was there light on the first day?

TL;DR:

Genesis teaches that light existed from day one because God Himself established it, even before assigning the sun its role on day four. The mechanics of light is not the focus but the truth that God created and unfolds creation by His intentional design and authority.

what does the bible say?

Genesis 1 shows that a form of light permeated creation from the first day even before the sun was created. The sun, moon, and stars were given their purposes on day four (Genesis 1:14-19), serving as ongoing markers for humanity rather than the initial source of light.

While we can't be certain of the initial light source, many possibilities have been proposed. One possibility is that the light on the first three days was a temporary protosun (i.e., protostar). A second explanation is that the light on the first day (Genesis 1:3) was a direct act of divine creation, with God Himself as the source. God does not need the sun, moon, and stars to provide light (Revelation 21:23). A third possibility is that the nearest star, our sun, was created on day one along with the other stars and celestial bodies ("the heavens" of Genesis 1:1). But these light sources were not yet visible to an observer on earth, due to the initial cloud cover. The "making" of the sun on day four refers to its functional appearance and role in the earth's environment, not its physical creation, which took place on day one with the other stars.

from the old testament

Genesis 1:1 says "In the beginning, God created the heavens and the earth." The term heavens refers to the sky and celestial bodies, which includes our sun, the nearest star. The term create (Hebrew bara, Strong's H1254) means to shape, fashion or create something new, fresh, and good. Bara is only used regarding God's creative work. It could mean to create out of nothing (ex nihilo), such as the physical universe, or it could mean to create out of something, such as Adam and Eve.
On day four, "God made the two great lights—the greater light to rule the day and the lesser light to rule the night—and the stars" (Genesis 1:16). Here the verb make (Hebrew asah, Strong's H6213) means to do, prepare, produce, or make. Asah can be accomplished by God or man, instantaneously or involving some process.
In the creation account (especially Genesis 1:26-27 and 2:4), both created and made are used in reference to ex nihilo creation events, and both are also used in reference to things God made from previously created material. Both verbs describe divine creative acts, with bara emphasizing the divine origin and asah focusing on the process or result. This is illustrated next.
Observe that on day one God Himself separated the light from the darkness (Genesis 1:4), while on day four God set the sun, moon and stars in the sky to carry on with the separation of light from darkness (Genesis 1:17-18). So the night/day cycle was initiated and controlled by God from day one, while the sun and stars were not visible until day four. Thus, day four highlights God having a distinct purpose for the luminaries He made: to mark times and seasons for humanity (Genesis 1:14-19).

from the new testament

One theory about the light that existed before God created the sun is that the light emanated from God. This theory is plausible considering James calls God "the Father of Lights" (James 1:17), and Revelation 21:23 describes God as the source of light in the new heavens: "And the city has no need of sun or moon to shine on it, for the glory of God gives it light, and its lamp is the Lamb."

implications for today

Like a pebble on a lake, a conflict has wider reverberations than just the two opponents. Eventually, most observers pick a side. This can happen with with conflicting ideas, too. When science and faith appear to be in conflict, leaving us unsure what to believe, we should trust the Bible and wait for further light on the details. We should also not expect Scripture to do what it was not meant to do. For the ancient Hebrews reading Genesis, the most important truth revealed was the fact of creation by God and understanding our role in His orderly design. The emphasis of the author was not to provide us with scientific or exhaustive explanations as to how the different aspects of our universe work.

We may not understand all the details behind creation, but we know that God is the Author of all. We can trust that He has revealed Himself through creation, His Word, and His Son. And because we know Him, we have faith that we will one day spend eternity with Him. Until then, we can use science to help us understand what He has done, leading us to awe and worship of our Creator, who spoke all things into existence with purpose and order.

As we hold Scripture as our ultimate authority, we can patiently explore the created world with humility, trusting that all truth ultimately points back to Him. In doing so, our study of creation becomes not a source of doubt but an invitation to worship the Creator who is both beyond our full comprehension and intimately known through Christ.

understand

The Bible is silent about the physical source of light for days one through three.
Several possibilities for the light source have been put forth.
We must understand the intent and boundaries of both science and Scripture.

reflect

How do you reconcile your understanding of the purpose of the celestial lights (sun, moon and stars) with what the Genesis account says?
What are some other science-faith conflicts that you've faced as a Christian, and how have you reconciled them?
In what ways does this passage invite you to worship God for who He is, even when you don’t have all the answers?

engage

How does the beauty, vastness and orderly design of the universe help you give glory to God (Psalm 19:1)?
How can Christians best engage with those who think the Bible contains contradictions?
How can we encourage unity among Christians when disagreements arise about how to interpret details of creation?