The length of Christmas lights needed for a tree depends on the size of the tree and the desired effect. A small tree may require only a few feet of lights, while a larger tree may require several hundred feet of lights to achieve full coverage. Additionally, it's important to choose the right type of lights for the tree. Incandescent lights are the most traditional option, but they can get hot and are not as energy efficient as LED lights. LED lights are a better choice for a tree as they are more energy efficient and don't get as hot.