You don’t need a four foot long light fixture to illuminate a four foot long reef aquarium. You can actually get away with a three foot long fixture, or even smaller. The only thing you need to worry about is lighting up the areas where corals will be present. Keep in mind though that going with a smaller fixture means the aquarium will have darker areas in the corners that would normally be lit up to some extent had you gone with a longer light. Using this same logic, if you want to go with individual pendants, you don’t need extras over areas where there are no corals. However, you might not like the look of dark spots in your aquarium, but you won’t have as high an electric bill going this route.