why you see light before you see a person appear?

Answer 1

I don't quite get the question. Our eyes rely on the stimulus of light to see. We see an object because it has reflected light into our eyes. We then recognise it's a person because our brain breaks down all the cues and stimulus and checks against our memory for recognition. All this takes time. Presumably light travels much faster than a person to you; added to that you need light to see anything, light coming off the person will always arrive before the person whether to your eyes or to your consciousness.