How does the shape of a leaf help it to use sunlight?

As much as I know... Broader, fuller leaves will be nearer the base because they are shaded by the upper tree canopy. If they are broader, larger, or have less exaggerated lobes then they have more surface area to catch what sun-rays they can. Likewise, leaves at the top of the canpy are distictly lobed, smaller, etc, because they have a greater exposure to sunlight. They can't typically absorb as much light as they are exposed to, so they have less surface area so they don't absorb too much and litterally get burnt out. Other shape characterisitcs are typically due other environmental pressures over time.