It's more than just being safe, it's the LAW in Iowa.
According to Iowa Code 321.384:
Every motor vehicle upon a highway within the state, at any time from sunset to sunrise, and at such other times when conditions such as fog, snow, sleet, or rain provide insufficient lighting to render clearly discernible persons and vehicles on the highway at a distance of five hundred feet ahead, shall display
As reported by Radio Iowa, legislators claim that it is unlikely that the Iowa lawmakers will make driving while handling a smartphone illegal. Right now it is illegal to text and drive in the state of Iowa. However, people cannot be ticketed just for having their phone in their hand.