Wyo. Stat. § 31-5-911: Visibility distance.

Whenever a requirement is declared by this act as to distance from which certain lamps and devices shall render objects visible or within which the lamps or devices shall be visible, the provisions apply during the times stated in W.S. 31-5-910 in respect to a vehicle without load when upon a straight, level, unlighted highway under normal atmospheric conditions unless a different time or condition is expressly stated.