What was the first light? The one that illuminated the first day of creation. The sun, moon, an stars weren’t made until day four. The word for Light differs from that of the light of the sun and moon.
In Genesis 1:3 the Hebrew word for light is “owr” and simply means light. In Genesis 1:14 when God created the sun and moon the Hebrew word for light is “ma’owr” which means “a luminous body.” So in creating the Sun and Moon, God was gathering the light into a luminous body, the Sun, to light the day. He then created the Moon and positioned it to reflect a portion of the Sun’s light onto earth during the night time.