At night, under-car neon lights produce an eerie effect, simulating some kind of science-fiction-esque warp drive. While these lights might be aesthetically pleasing, they can be distracting. Too much light may be overshooting the vehicle. While legal in Idaho, the state does have ordinances that regulate their usage.
Front of Vehicle
The city of Idaho Falls quoted state laws when it stated that lights cannot extend past the front of the vehilce. This is for the actual illumination area. Since most lights are designed to illuminate the car underside only, most are in compliance.
Rear of Vehicle
Another state law is that the illumination area cannot extend past the rear of the vehicle. Again, because most lights are underside only, this should not present a problem.
Whole Car Compliance
The entire car, both front and back, must be in compliance. For marking and illumination lights, only white and amber are used in the front. For the rear, only red and amber, white for the license plate light.