The main advantage of adding lights to your poles is easy accessibility. Instead of needing to remember to bring a flashlight or headlamp, you have light right at your disposal. Also, if a hike takes longer than you expect and you didn't plan on bringing a light source, you can still find your way without tripping on unseen rocks and such.
Also, keep in mind that the instructions here apply to both poles; they're made in exactly the same way.
Step 1: Materials
1x Pair of trekking/ski poles (you can either buy some or modify ones you already own)
4x Single AAA battery holders (Something like these: http://www.frys.com/product/2966145 - you may be able to find less expensive ones locally, however. Otherwise, two of these are even better: http://www.radioshack.com/product/index.jsp?productId=22874876&prodFindSrc=cart)
2x Bright white LED lights (something like these: http://www.radioshack.com/product/index.jsp?productId=3060980)
2x 5mm LED holders (something like this: http://www.radioshack.com/product/index.jsp?productId=2062559 - if you want to save a bit more money, these aren't entirely necessary. They'll increase the range of the light, though, so they're recommended)
2x Small SPST switches
A bit of scrap sheet metal
A few feet of electrical hookup wire (I used 22-gauge)
Stronger glue (Gorilla Glue, JB Weld, Super Glue, etc.)
Solder of your choice
A Dremel or other rotary cutting tool
An electric drill (either handheld or drill press)
A hot glue gun
A soldering iron
A few clamps (for holding parts in place while glue cures)
Once you have these materials, you're ready to start!
Step 2: Cut Holes in the Poles
The battery holder holes don't need to be incredibly precise, just large enough to snugly accommodate the holders. Hold the holder next to the pole where you want the hole to go (approximately the upper-middle part of the pole) and loosely mark its perimeter. Transfer the markings to the other pole, and cut it out with a Dremel. Try not to damage the part you're cutting out, as you'll need it later.
Then, decide where to drill the holes for the light and switch. The light can go pretty much anywhere, just make sure it's at the front of the pole - try holding the pole in your hand, and mark which side is the front. The switch hole, however, should be no more than half an inch away from the top or bottom of the rectangular hole. If it's farther, it'll be a huge hassle to mount the switch.
Once you've decided on location, drill each hole on each pole with the correctly sized bit. The holders I used needed a 5/16 inch bit, and I widened the hole a bit with a Dremel to decrease friction.
Remember to be careful when drilling on a cylinder, as larger bits tend to slip. Try making a pilot hole first with a smaller bit.
Step 3: Prepare the Electronics
Now, do the same thing with each switch.
After this, you're ready for final assembly.
Step 4: Assemble the Circuit
First, solder the negative wire of the battery holder to the negative end of the LED (protect all solders with heat shrink). Then, solder the positive end of the battery holder to one side of the switch. After that, solder the other end of the switch to the positive end of the LED.
At this point, you should test the circuits of each pole. Put batteries into each holder and flip the switches a few times. If everything is working, move on. If not, check all the connections and make sure there are no shorts.
Once all the wires are secured together and the circuit works, fasten in the light and switch. I secured the light with a bit of hot glue on the inside and my switch came with a nut to hold it in place. Next, compact the loose wires into the pole so there's room for the battery holder to sit inside without sticking up. Secure the holder in place with some hot glue, and the circuitry is done!
Step 5: Attach the Battery Cover
After the glue has cured, remove the clamps and bend each newly attached prong slightly downward (downward as in pointing into the pole body). Then, cut a small groove at an end of the battery compartment in the pole body to. Play with the size to see what works best.
After cutting, put some electrical tape on the underside of the cover as insulation from unwanted electrical connections.
To attach the cover, slide one prong into one end of the battery compartment hole and the other into the groove you just cut. These will hold the cover nicely in place.
Step 6: Recap
I think there are many improvements that can be made to this design, especially in terms of the battery cover and waterproofing capabilities. With some design work and precise equipment, something like this could eventually become a marketable product.
In seventh grade I presented this idea in an invention competition at my former school, and it won second place. The first place winner of that year is now working on making his invention into a small business with the help of a program hosted at Harvard University - only nine others besides him on a national basis were accepted. The competition was no small matter, to be clear. I think the idea could have potential, and so do others, apparently. I'd love to see what ideas the maker community can come up with: improvements, additions, anything.
I hope this Instructable, along with my others, can serve as inspiration for bigger and better things. Thanks for looking!