DIY Bicycle Trail Light

I’ve recently dipped my toe into mountain bike racing.  I realized there aren’t any mountains in North Texas, but there are lots of trails.  It’s also hot as blazes out so the endurance races I’ve been doing go from 6-11 PM and a light is a requirement.  Riding a trail at night requires a fairly bright light.  The first race I tried to use a hiking head lamp and I thought I was going to crash about a thousand times.  Most decent bike lights start at 100-200 lumens and around $100.  They go up to 1000 lumens and cost a couple hundred.  There are $30 bike lights available but those are in the 20-50 lumen range and they glow more than they shine.

At this point $100 is too much of an investment for me so I thought it’d be more fun to build my own bike light.  The LED technology in the flashlights advances really fast so the best lumen for your buck comes from general use flashlights instead of biking specific ones.  Costco had 220 lumen flashlights in a 3 pack for $15.  The only downside is that their 3 AAA batteries only last 1 hour.  I wired in 3 D batteries in an external battery holder and I should have 10 times the capacity (12000 mAh vs 1200 mAh source).

Here is my step by step instructions.  Total cost at the bottom:

Used drill press to drill hole in side. You can see the battery holder inside, but that wasn’t in there for the drilling.

Battery holder removed

Power chord soldered into the battery holder

Flash light reassembled

Battery holder on other end of power chord

Drilled a hole in an old water bottle and routed the power chord through there before attaching to battery holder

Assembled and working on external power



$5 Flashlight ($15 / 3pack at Costco)
$1 Power Chord (18/2 wire at Home Depot $.42/foot)
$3 Battery Holder ($2.03 + shipping from McMaster-Carr)
$13 Flashlight handle bar mount(not pictured, Amazon)
$3 D Batteries (Not sure on price, these came from my battery drawer, not sure what I paid for them)
$0 water bottle (free from doing a triathlon)

$25 total

I also bought a $5 handle bar mount but it doesn’t hold the light still through the bumps on the trail so the $13 is necessary.  I made a second one of these and put the batteries in my Camelbak and velcro+zip tied it to my helmet and it worked awesome as well ($12 total since no fancy flashlight mount required).

At the last race there were certainly brighter lights out on the trail, but there were also worse lights.  It was a totally workable solution and I feel like I saved at least $100 over buying two cycling specific lights.