Idaho Code § 49-924: Single-beam road-lighting equipment.

Head lamps arranged to provide a single distribution of light shall be permitted on motor vehicles manufactured prior to January 1, 1955, in lieu of multiple-beam road-lighting equipment specified in this chapter if the single distribution of light complies with the following requirements and limitations:

(1) The head lamps shall be so aimed that when the vehicle is not loaded, none of the high-intensity portion of the light shall at a distance of twenty-five (25) feet ahead project higher than a level of five (5) inches below the level of the center of the lamp from which it comes, and in no case higher than forty-two (42) inches above the level on which the vehicle stands at a distance of seventy-five (75) feet ahead.

(2) The intensity shall be sufficient to reveal persons and vehicles at a distance of at least two hundred (200) feet.