What other information have you been given about this topic? It seems a bit vauge at the moment. However, if you have been given nothing except this title, you can make that work to your advantage as you can shape the essay the way that you want to. Your first start would be brainstorming the topic and coming up with ideas and thoughts surrounding this phrase. Clearly it comes from the Bible when God created the earth, but are there any other concepts or ideas that you could apply it to? Are there any other moments in history that you could refer to through this allusion?
One idea that I have had is thinking about famous revolutionary inventions or discovers that really represented the discovery of "light" for mankind. You might like to pick either one of these and focus on it in depth, talking about how important this invention or discovery was, or you might like to pick three or four such inventions and discoveries over the course of history and do the same thing, but much more briefly. This would be an interesting take on the question. Hope this helps and good luck!