Having a headlamp that illuminates your favorite running path is a good start, but you also want a running headlamp that’s comfortable and fits properly. Most headlamps have an adjustable strap for a more secure and personalized fit. If you plan on running outdoors frequently in inclement weather, consider a headlamp that’s at least water resistant. A handful of models are weather resistant and are built to withstand tough conditions such as rain and sleet.
Headlamp brightness is measured in lumens. Many of the best running headlamps offer at least 100 lumens, which is ideal for road running. However, if you’re planning on using the headlamp on trails, consider going up to 200 lumens or higher. A greater output means better visibility even on the darkest trails. Another feature for trail runners to consider is an adjustable light or at least a beam that can alternate between a broad output and a narrow beam.
Source: Heavy Sports