LED Light Sizing

Hey guys, so I am looking to now purchase LED lighting for my tank. Its 48" wide and I was wondering does this mean that it absolutely needs a light that spans the length of the tank? Will a 36" adjustable light fit and will this be enough for the tank?



Or should I really be getting a perfect fitting light?



This is the one I was looking to get. It has day and night mode and is 36"