Origin site is here (http://www.nejm.org/doi/full/10.1056/NEJMicm1104059#t=article)
He is a truck driver and he had sun on one side of his face only.
You can notice which side is sunned one easily.
More than many facts and studies on UV burning, As you know 'Seeing is believing'
Please be mind that sun cream is very important to not only good health but your appearance.