Secondary light source

One of the most useful assumptions in graphics is that there is "direct" lighting and "indirect" lighting.  Mirrors always mess that up.  Here is an example of a shadow cast by "indirect" light:

The shadows on the ground are from the Sun which is well above the horizon.  The dimmer shadow in the doorway is from a bright "secondary" light.

The light comes from a car:

The shadow is cast from the highlight on the red car.  Interestingly the iPhone camera makes all these bright hightlights about the same, whereas in real life one is MUCH brighter.  Clamping FTW!

For games and historical visualizations it is probably best to just pretend those secondary specular lights are not there.  However, for predictive applications they should be tracked.    Dumping the whole concept of "direct" light is not irrational in such cases.