1. A vision system for a vehicle, said vision system comprising: at least one imaging sensor having a forward field of view with respect to a direction of travel of the vehicle, said at least one imaging sensor comprising a two-dimensional array of photosensing elements, said at least one imaging sensor sensing images of objects in said forward field of view; a control responsive to an output of said at least one imaging sensor, said control modulating at least one headlamp of the vehicle in response to said output of said at least one imaging sensor; wherein said control processes said output of said at least one imaging sensor both (a) to identify a headlamp or taillight of another vehicle in said forward field of view of said at least one imaging sensor and (b) to determine a distance between the controlled vehicle and said identified headlamp or taillight of another vehicle, and wherein said control determines the distance from the controlled vehicle to said identified headlamp or taillight of another vehicle in response to a size of said identified headlamp or taillight in said sensed image; and wherein said control modulates the at least one headlamp of the vehicle responsive to said processing of said output of said at least one imaging sensor.