Directional light is mainly used for simulating light coming from very large and far light sources, such as the sun and the moon. Because the light source is very large and far, we can assume that all light rays are parallel to each other, which makes the calculations relatively simple.
The following screenshot shows the same model we used to demonstrate ambient light under directional light:
When rendering an outdoor scene that uses directional light to represent the sun or the moon, it is very common to combine the directional light calculation with the ambient light calculation. However, you may still want to support ...