The people who really understand this subject are the ultramarathon runners. These races are typically either 50 miles or 100 miles. The 50-mile race can be done during daylight hours, but the 100-mile race typically gets into some night running (except for the awesome winners). In the old days >20 years ago, they had to use incandescent headlamps with ordinary batteries, but the incandescent bulbs would break or burn out, and they were just kind of a pain with lots of battery changes. Decent LED headlamps were almost unheard of at that time, so enterprising runners fabricated their own fluorescent lights into a waist-lamp. Typically, it was a six inch tube across the front, and a stack of batteries on the back of the belt. That was good for two reasons. First, it put the light down low where it would raise some good shadows on the trail. Secondly, it was wide enough to light up a lot of trail width. You really knew when those guys were coming along! Then about 15 years ago, the good LED headlamps came along. Most of the early ones required 3 AA cells in order to drive the typical LED devices of the day. Later on, charge pumps changed all of that so that in some cases a single cell or pair of cells will drive the LED. Still, most LEDs emit a very narrow spectrum of light, so things don't always look the same color as they would with natural sunlight. That may or may not be a problem.