How much to spend?
Bike lights range from $20 to $1500 for a set. For a rechargeable LED system that you want to see with at a good riding speed, you want to spend a minimum of $50. $100-$200 is the sweet spot for a reliable system you can use for the next few years.
LEDs and rechargeable batteries?
Rechargeable systems of today feature lithium-ion batteries. Like cell phone batteries, they can be charged about 500 times, making them an inexpensive and environmentally sound alternative to disposable batteries.
LEDs are the latest bulbs available today and they are brighter and more efficient than the halogen and HID bike lights of old, Make sure you are buying an LED bike light.
How much light? What is a lumen?
Light output is measured in Lumens which is the total light output of a light throughout the entire beam pattern. This output can only be measured accurately with a light integrating sphere which is a scientific instrument usually costing about $25,000 and requiring an engineering degree to operate. For reference, a 100-watt lightbulb is about 700 lumens and car headlights put out about 3000 lumens
For MTB trail riding, 700 Lumens is the minimum. It allows you to ride at a decent speed with a good sized beam pattern that allows you to clearly see the periphery. An even better setup is two lights: the more powerful light on the handlebars at about 1000 Lumens and a 700 Lumen light on the helmet.
For commuting, since streets are brighter, 400 lumens is the minimum for seeing where you’re going and avoiding obstacles. To be seen by vehicle drivers, you want 50 lumens on the front and rear of your bike so improve your safety.
The faster you ride the more light you need in order to not “outrun” your beam. That means 2000 Lumens on your bars and 1000 on the helmet.
Picking a beam patterns
After output, the next most important attribute of lights is beam pattern. Beam pattern is the shape and size of the light that is projected by the light. As a light gets brighter, you want to look for a wide and even beam pattern. A bright light is more useful when the beam is dissipated over a wide area evenly, while also projecting out a fair distance.
A clean beam pattern that doesn’t have hotspots or dark artifacts is desirable, too. And finally, color is a factor as well. A white, slightly yellow (or warm) color is best, as it reveals trail contours better and is not harsh on the eyes. Pure white lights or blueish lights may appear bright but they are difficult to see with and increase eye strain.
Helmet or bar Light?
The bar light is ideal for a powerful light that is out of sight, out of mind, with the ability for longer battery run times. A very wide beam pattern is desirable to see the periphery. A helmet light is ideally a smaller light that’s lighter with a tighter beam. That beam can see a long distance and will follow the riders eyes to help them see through corners and switchbacks. Ideally, the rider will have both lights complementing each other and lighting up the periphery with the bar light and seeing through corners with the helmet light.
If the rider can only have one light, the helmet light is the more common choice. It allows the rider to use the Lumens more efficiently, aiming left to right with head movement.
Heat and run time
Run time is the total time the light runs in high power until the light shuts off or dims down to half of its brightness as the battery loses energy. Most self-contained (flashlight style) lights last 1 hour at full power. The ones with an external battery last about two hours. At half brightness, runtime will double and so on.
So what we recommend is get the brightest light you can afford and run it at half power or 1/3 power when you are not descending at full speed.
When the bike is in flashing mode, it typically lasts 10x its normal run time.
Self-contained or wired?
All bike lights used to be wired, but the emergence of LED and lithium batteries have allowed bike lights to combine the light head and battery into one compact package. The big advantage is no wires and connectors to fiddle with. The self-contained bike light can also be used around the house or campsite as a very powerful flashlight.
If you need lights that last a very long time at full brightness, then get a wired bike light. But for most folks, get a self-contained LED light. It is convenient, bright and you can use it as the ultimate flashlight around the house when not riding.
Check here for our 2018 Best Trail Lights Recommendations.