I would recommend a handlebar light AND helmet light for street and trail riding at night. I bike commute at 5:30am and there are quite a few "no cop, no stop" drivers running stop signs that early in the morning. Having a helmet light to shine on vehicles approaching the intersection and alerting them when I have the right away is just added safety for me. The helmet light works very well when I take 90 degree turns at night to illuminate the side road so I can avoid anything in the turn at +15 mph that might make me lose traction (water, sand/gravel, pot holes, road debris, road imperfections, etc...).
I also like the helmet light on the trails since it can illuminate every where you look; especially, around corners. If you pass other riders, you just have to tilt your head up or away so you don't night blind them. If you need to stop at night, you have the helmet light to see what you are doing (once had my right shoe lace tangled in the crank, lost water bottle on a trail over a hard bump, and left crank arm fell off at 20 mph commuting to work).
I have an el-cheapo TianNorth 9T6 15000lm 3 mode light with 18650 battery pack with extra battery pack, Amazon, $40 for light, $30 for extra battery pack. Not even close to 15,000lm, more like 800-1100lm. Has a very wide and long beam to light the road for morning commutes (won't out run your light at 20-22 mph). Extremely bright strobe for daytime riding in traffic. Only use this light on paved roads or alone on trails because it will night blind other bike riders on trails.
I also use Topeak Mega Whitelite 10w with 18650 battery pack for my helmet, $400 regular price, can get lucky on eBay like I did and get it for $70-$100. Very bright leaning more towards spot than flood light type of illumination. Very handy to see 3X further down the trail or road. Spotted and avoided a few skunks, porcupines, and coyotes on the trails in ABQ near the river. I also spotted a wolf and a lot of elk and deer on a trip to the Grand Canyon in Nov with the Topeak.
The only downside I found with 18650 batteries is they deliver full power until they run out. My el-cheapo light just dies when power is low. The Topeak gives me a warning when reaching low power. I would make sure if you have a feature that notifies you when power is low or the 18650 powered light will die right in the middle of your ride. Extra battery packs and a $15 LED flashlight for back-up you can attach to your helmet or handlebar can't hurt.
I also have two Light and Motion Vis 180 Bike Tail lights, $80, Amazon, or $45-$60, eBay. One for my rear bike rack and the other on my helmet. Very bright and can be seen in the daytime and it has a slow strobe feature instead of the seizure causing fast strobe. Has a setting of just a yellow light if you travel in a pack and you don't want to night blind the bikes directly behind you. USB rechargeable and I just recharge once a week after 40-60 miles of bike commuting.
