Helmet Mount

The advantage of a helmet mount is the light is higher off the ground and has a better angle
of attack to the ground. This better angle of attack puts more viewable light on
the ground. None of the light’s output is wasted by shooting it into space. You
can aim the light by just moving your head up and down or looking around. This
allows you to inspect technical descents more closely or look down the line
through quick “S” turns. For fast turning single track helmet lights are a must.
The downside of helmet lights are they don’t work very well in dusty conditions.
Some people feel they lack contrast. That the light washes out on smaller
obstacles. This is caused by the lights angle of attack. It illuminates both
sides of the obstacle. They also don’t work well in drizzly rain or fog. The
light will reflect back into your eyes off of the water droplets.

Handle Bar Mount

The main advantage of this type of system is the light cast shadows on the ground. It is
these shadows that many people feel give them the contrast that allows them to
ride at full speed. Bar lights work better than helmet lights in dusty, drizzly
rain, and foggy conditions because the light does not reflect back into your
eyes. But the reality is, in these conditions your really just measuring degrees
of better in crummy conditions.
The downside of bars lights are they don’t work well in twisting turning single track because the light quite often is aimed the wrong way. Since the light is relatively parallel to the ground you waste a fair amount of your light output by shooting it into
space.