Dunno. the Bible doesn't say what the light is, it just says: "And God said,Let there be light, and there was light."
I'm interested in hearing how you dance around this one. The only natural sources of light worth mentioning that effect our planet are our star the sun, the moon, and the rest of the stars in the universe. Please tell me what this magical source of light was that lit up the earth before the G man made the Sun.
What if it was a spectrum of light not visible to human eyes, like light with wavelengths that we cannot see, such as: radio waves, microwaves, infrared, ultraviolet, X-rays, or gamma rays?