In reply to idiotproof:
I think it depends on 2 things.
1, are you doing any speed work on these runs?
If so you need a good far reaching spot and a handheld high intensity led.
2, Will you be running over the same bit of ground or on easy formed trails?
If you will be then you should just take it easier till you know the trail and just go with a high intensity hand held.
I do alot of trail running at night and find that this combintaion works best as I can vary the amount of illumination without excess weight on my head.
Rob