When you create an Ambient Light, there is no specific direction this light comes from. There is no relationship to any light in our real life. Ambient Light applies the color globally, it also does not contribute to any shadows.
Only the two parameters color and intensity are supported (but not position, rotation, and scale):
<a-entity light="type: ambient; color: #BBB; intensity: 1" ></a-entity>
<a-light type="ambient" color="#BBB" intensity="1" ></a-light>
It is also possible (but not recommended) to add the Ambient Light to any Entity.