In the words of the prophet, "Sez who?"
They glowed in the dark?
Citations, please?
In other words, sunlight. Now there's a surprise!
Oh, so You Don't Believe The Bible, eh?
For my citation, Id reference old testament Biblical scholar and expert of ancient near east background of the Bible, Professor of Old Testament studies at Wheaton College and former professor at Moody, Dr. John Walton. Specifically his books, The Lost World of Genesis One, and the Old Testament Background Bible Commentary.
Perhaps you're not understanding what I am saying.
Genesis often uses phenomenological language of the ancient authors. For example, the blue sky is described as "the waters above", but the sky of course isn't literally made out of water. That's just how ancient Egyptians and Babylonians described it.
And when it comes to the question of light before the sun, we see this occurrence in Egyptian creation texts as well. Coffin texts, pyramid texts, and the Memphite theology.
And when Egyptians described light before the sun, they were describing lights appearance before the sun god Ra had appeared above the horizon. It would logically follow that Genesis, which contains the same creation order as the Memphite theology, is simply doing the same thing. It's describing lights appearance in the sky, before the sun had risen and before the sun was actually appointed to rule the day.
I will additionally cite Old Testament scholar, and PhD Bible professor of Capital Seminary, Dr. John Soden, and Old Testament scholar Johnny Miller, PhD in Old Testament from Dallas Theological Seminary, in their book "In the Beginning...We Misunderstood":
"The starting point: Before the beginning of creation, there was an infinite dark, watery, chaotic Sea. There was nothing above the sea or below the sea - The sea was all there was. Immersed in the sea, Atum, the creator God and source of everything, brought himself into existence by separating himself from the waters. Egyptian cosmologies that view Amun has the creator, or even as one of the four initial qualities of the pre-creation matter from which creation emerges, within also understand the wind to be present in the water, because Ammon was also god of wind. Since Atum, Amun, and Re are all connected with the Sun, light was men in existence, even though the sun itself had not yet risen."
So what I am saying is, the light before the sun was viewed phenomenologically as something independent of the sun.
And in Egyptian texts, the god associated with the light was created in the chaotic waters and rose up out of them. Thus light existed before the sun was created. Entities beyond the firmament, those in the waters, did not yet exist until they were appointed a purpose.