For mounting a battery powered light I used a long M5 bolt, some washers and a couple of nuts, and a piece of wood with a cylindrical shape that was about an inch (25.4 mm) in diameter that I drilled a hole through. I intentionally drilled the hole through the wood off to one side, not concentric, because I wanted to lower the center of gravity. You can mount in a midfork rack mount (if Nomad Mk II, M6, not M5).
Best done up around the midfork rack mount or higher, any lower and you get too many shadows from uneven terrain.
The attached photo is a dynohub powered light, not battery. But I attached this photo because it is NOT what I recommend, I only show this as an example of what will give you too many shadows in uneven ground because the light is too low to the ground. In this case I mounted the light in the fender mount, as this bike (not a Thorn) did not have a mid fork rack mount. I plan to mount this light up higher in the near future.