How would you know it’s light if there was no dark to contrast it ? Light only exist because dark surrounds it, and dark only exists because light surrounds it. One cannot exists without the other.
If I show you a black circle on a white paper you would point at the black and say “this is the thing that is drawn on the paper”. If I were to show you a white circle on a black paper, you would point at the white instead with the same statement. If I showed you an all white paper and told you there is a white circle on it, you would tell me I’m an idiot and that there is nothing there. Contrast is why something exists.