Genesis 1:14-19

14 And God said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days, and years: 15 And let them be for lights in the firmament of the heaven to give light upon the earth: and it was so. 16 And God made two great lights; the greater light to rule the day, and the lesser light to rule the night: he made the stars also. 17 And God set them in the firmament of the heaven to give light upon the earth, 18 And to rule over the day and over the night, and to divide the light from the darkness: and God saw that it was good. 19 And the evening and the morning were the fourth day.

Let there be lights in the Heavens to divide the day from the night... Notice God has not changed the length of the days or night here, but for He has created a new order in which the light should be dispensed from actual physical bodies. As with the rest of creation God has created an order in which everything is self sufficient within the created universe to supply the needs to sustain life. It was not necessary for God to create these lights, He could have continued to be the source of light forever, however just as Jesus and the plan of salvation was in place before the foundation of the earth was formed, God had reason to create a source for light within the humanly known universe to lay the foundation of belief and faith without seeing. Jesus said to Thomas, you believe because you have seen, blessed are they that believe without seeing. Had God not created elements to disperse the light, how much faith would it require if we knew light was supernatural? Let us also not forget that these lucid bodies of light are performing in obedience to God, they glorify God because they are doing exactly what God commanded them to do, let us remember to glorify God by doing what he asks us to do.