No, no.
"Let there be light" came AFTER the Big Bang.
God had to create the universe first. Light was only later.
Genesis 1:1 describes the cosmological beginning of the universe (which includes light, but not the "fiat lux" variety). Genesis 1:2 describes an Earth that has already been formed, and moves the point-of-view of the narrative to the surface of the Earth. Genesis 1:3 describes the preparation of the Earth for life (or renewed life, if you interpret 1:2 as describing an extinction event). That's where, "Let there be light," comes into play. I'm not sure why there wasn't light before -- perhaps the sky was heavily overcast, or nothing had evolved eyes yet.