Where to install? The right spot for your helmet light
In general, mounting your helmet light on an MTB-helmet is the optimum solution for extreme mountain biking in the dark. The cone of light falls along your line of vision and allows you to ride with increased foresight and speed. If the lamp is mounted on the Handlebar, the light cone falls rather onto your steering path. The latter option can be especially unsteady on winding trails, and can make navigating them difficult. That said, helmet mounting also has its disadvantages: powerful headlamps are oftentimes heavier due to the large size of the battery, and carrying additional weight on the helmet can quickly become uncomfortable. However, you can carry large batteries in a backpack or jersey pocket and connect them via an extension cable. The optimal combination, therefore, is an extremely bright lamp attached to the handlebars with its battery mounted onto the frame, and a smaller lightweight lamp installed on the helmet.
When putting together a combination of both helmet and handlebar lights, make sure to test out how much weight you can comfortably carry on your helmet, and make sure to determine if handlebar mounting is even an option for your bike.