Update 3/22/06:  Pivvay (Chris) has done a great write-up on DIY LED lighting.  It's a bit of work and no guarantees you will have light out in the boonies, but check it out:  http://slipangles.blogspot.com/2006/03/geek-this.html.

Part 1 of this series addressed nutrition and supplements for 24 hour solo efforts, geared towards an experienced racer who is doing their first solo event.  Picking up where I left off, here's another bit of Q&A from Yuri.

Yuri: How many lighting systems should I have and, do you wear a system on your helmet as well?

Dave:  Great question.  24s can be won and lost in the dark, trust me on this one.  For starters, there's a lot of info at MTBR on lights.  Another great review of LED light systems is at gearreview.com.  There are so many choices out there...I encourage anyone reading this with different experiences to post a comment of favorite setups. 

It depends on the style of riding and the course demands...but I generally prefer two light systems.  On the bars I'll have a bright (HID) wider beam light, and on my helmet a narrower spot beam.  The helmet light doesn't have to be quite as powerful as the bar light - it is simply a spot to fill in the gaps, especially in twisty singletrack so you can see where you are going as opposed to where your bars are pointed.  I also like the helmet mounted light to be narrow and bright enough that it can throw light farther than the bar light.  This is especially helpful if there are high speed sections on the course.  At Moab, for instance, there are some straight shot gradual descents that are rippin fast - if you have enough light, anyway (unless of course you just use the force). 

Also, some types of lights seem better for certain types of terrain.  For example, if it's dark terrain, like high-country in the woods stuff, I prefer brighter light, like an HID.  If it's desert terrain, like Moab, I like yellower halogen light possibly mixed with HID light.  I've only used one LED system to date, and this is an area of keen interest as the systems generally last longer and are lighter.  Experiment as much as you can before the race to determine what works best.

I wouldn't consider any light system that I didn't trust to run for 2 laps, about 3 hours.  Also, the batteries must be able to charge up within the same timeframe - 2 laps.  This way, you can get by with 2 light systems and 4 batteries.  This is what I'd consider the bare minimum - if you can beg, borrow or steal a couple of backup systems and/or batteries you'll have more piece of mind.  24 hour events require a backup light source of some sort, and this requirement is satisfied by a second light.  That is a great argument for two light systems.  You can get the charging done by neutral support probably, depending on the type of systems and support offered, or you could do it yourself with a power inverter and your car battery.  I've been doing the latter for the last 3 years.  The inverter can be found at Radio Shack.  I can charge multiple batteries and run a low wattage shop light through the night, works a charm.  Here's my setup:

Before the race, you'll want to make sure you have it all dialed in.  If you need a connecting wire from the bike mounted battery to the bar-mounted light, zip tie it in place...if you need an extension from the helmet mounted light to the battery, make sure you've got that worked out and it works.  Sometimes long cords develop shorts at the worst possible times.  I find that the routing of the wire from the helmet to battery is non-trivial, in particular.  Good to have it figurred out so it isn't in the way on race day (night).

As a final note on night riding, take good care of your eyes.  I can't stress this one enough...  Always wear eye protection, no matter how much it might feel good to go without (initially).  The colder the temps, the more critical this becomes.  Evolution, for example, has set up some deep water fish with mechanisms that keep the eyeballs at a constant 20-25C.  It turns out that the "speed" of sight is greatly determined by eye temperature.  I can tell you from personal experience, if you scratch your eyes with dust or whatever, then it gets cold, you are going to be so pissed as you crawl in your sleeping bag listening to the race carry on despite your temporary blindness.

So there you have it.  Stay tuned for more rants and secrets.