Ambient Light

Because the ambient light can evenly illuminate all objects in the scene, it is often used to solve the problem of the backlight surface of the model is completely black, generally need to be used with other types of lights together. For example, if there is only directional light in the scene, it will look very dark at the backlight of the model.

Check Scene in the Hierarchy panel, and then set the ambient light property in the ambient component of the Inspector panel.