Humans can predict human behavior on the road. When machines drive, they will need to be able to predict and anticipate human behaviour much better than they presently can.
Human drivers, for example, know by intuition and experience that teenagers on a corner might step out and cross against the light, while a woman pushing a child in a stroller is more likely to obey the signal.
From the concept cars and lectures made at the last congresses and workshops, we can consider there are two ways to communicate with light: signs and signals meant for ambient humans (pedestrians, bicyclists, other drivers) to see on the vehicle itself, and markings "printed" with light on the road.
Communication by light signs and signals
This uses shape, colour, homogeneity, and intensity of light signals and signs.
BMW unveiled a car equipped with a green light on the front of vehicle to help pedestrians cross the road safely by alerting them that the car has "seen" them and will wait for them to cross.