Respiration and photosynthesis are completely two different process. Respiration has absolutely nothing to do with light, and that is why light doesn't affect it. As for photosynthesis, it cannot happen without light, so, obviously, the more light you put in, the faster it becomes, to a certain point, look back at the example i gave with the sheep. Now think about a wolf, put as much grass as you want, and yet nothing happens, because the wolf does not eat the grass. The wolf is your resiration process