I'm doing the "Run Nightly" half marathon at WWC next week.  I'm an experienced trail runner, but have not gone out in the dark, so this will be interesting to say the least.

I just bought a Petzl Tikka+ (140 lumen) headlamp.  Planning on also having some sort of handheld (maybe knuckle lights?), but trying to balance the need for it against the weight and inconvenience, etc.

I hope to do a test run beforehand, but out of town quite a bit before then so may not have the opportunity and may need to go in cold.

Would welcome any input on whether the handheld is necessary for running the trails and if so, which ones are recommended.  Plus any other night tips you can offer.

Thanks very much for your reply and input.  I was able to get out and do a trial run with the Tikka+, and will share how it went for anyone else that might be following this.

I think I have the same Tikka+ as you - it can put out 160 lumens in short bursts, but max 140 lumens sustained.  I tried all the power settings and the 140 lumens was just about good enough (a bit more would have been good, Black Diamond makes some headlamps with 200+ lumen output, which would probably be better for trail running but probably still not enough for riding).  

The lower outputs were definitely not enough to run with,  and the Tikka+ on highest output would not be sufficient for riding.    While the light was adequate, I did not feel comfortable running at a fast pace - no problem since with a half marathon distance I'm not going to be flying anyway - but for shorter and faster runs more output would be good.  

I also bought some Knuckle Lights, (but have not tested them yet), so hopefully that will help also.

The experience of night trail running was pretty awesome, especially after getting used to it...  You really can see where all the spiders are - their eyes light up like diamonds (and there are many spiders out there!).  The first time I encountered a larger critter (probably a possum) it was a bit unnerving to see a pair of eyes glowing back at me.   A few bats were flying around too.  

The light seems to attract insects, so (especially if riding) would recommend glasses to try to keep them out of your eyes if using a headlamp.  Also a terry cloth headband would have been good to help soak up the sweat and keep the headlamp from moving around too much.