Buyer's guide to mountain bike lights

What to look for, and how we test them

The world of bike lighting technology is packed with jargon and it can be hard to figure out exactly what you need without spending a fortune.

To cut to the basics, the only requirement for mountain biking in the dark is some kind of illumination. Even a basic commuting light can stand in, but you’ll quickly discover that riding can get sketchy very quickly without enough power to light the trail in front of you.

How bright is right?

The temptation is – naturally – to get as much power as possible. And power is good, but there’s much more to the story. If you tend to cruise climbs and cane the descents, you want max power for the sketchy bits. You can then toggle right back to save battery power as you trundle back up. If you’re more into mixed trail riding, you need good lights all the time and battery life is more important.

You may have a 1,500-lumen light, but if the battery means you can only run it at 50 percent power for a fast cross-country/trail ride, it’s less bright than a ‘weaker’ 1,000-lumen unit you can run at 100 percent. Given that battery life fades over time, having the extra capacity means you’ll get more years’ use from your light.

It’s also possible to have too much power – particularly in wet or foggy conditions, where bounce-back and glare mean you see less than with a less powerful unit. Riders with brighter lights behind you can throw your shadow down the trail, blotting it out.

In general, there’s little that will make you wish you had more power than a good average light produces. You’ll find you adjust to whatever you have, and that riders who are faster in daylight are still faster at night, regardless of what lights they have.

Overall, you need to pick a unit that suits your riding and your wallet based on the information we’re providing here.

Invest in a decent set of lights and you can continue riding throughout the winter

Related: Best mountain bike lights

What to consider when buying mountain bike lights

Fit: The first thing to check when buying is that the light and battery (if it’s external) actually fit on your bike – this is especially important if you’ve got one of the latest 35mm diameter handlebars or a compact, curvy, carbon fibre frame. It needs to be mounted securely too – a great lamp is no use if you can't fit it to your bar (or helmet), or if it just wobbles and points the wrong way when you do. A weak or loose bracket that suddenly twists or shakes loose on a rocky descent is a recipe for disaster, and a badly placed helmet light will drag your lid down or wring your neck. Also make sure you can position the light where you want it, and that it'll do the job. Check that bigger lights will actually fit on the curve of your handlebar without sitting at a crazy angle. 

Power: The next obvious criterion is power. Firstly though, you need to realise that ‘theoretical’ lumen counts, based on LED power and battery charge in perfect conditions with no heat issues or circuitry to reduce efficiency, are sometimes 30 to 40 per cent higher than the actual real-world ‘measured’ lumen output of a light.

Beam type: Power isn’t any use in the wrong place either, so decide whether you want a narrow spot beam for straight and fast riding or helmet use, a wider beam for slower, more technical terrain, or a balance of both – which is likely to be more expensive. If you ride really technical, twisty trails then a cheaper bar light and head light might give better overall illumination than a single more expensive light.

Battery life: You then need a battery that gives enough run time to cope with your longest rides, plus a bit extra for emergencies or when the battery gets old or cold. If you’re likely to be pushing its limits, check it has a battery indicator for rationing power, rather than relying on an emergency alert – these often come on way too late, and being able to check remaining run time is often nearly as important as actual battery life. Being able to run full power on descents or stop to fix a mechanical without worrying about getting stuck in the dark is vital. Sub-zero temperature can also sap battery life dramatically so buy a bigger battery if you like proper winter epics.

Controls: Ask yourself whether you want the convenience of a remote switch or the ability to tune power output, and are willing to pay extra for those features.

Separate lights or all-in-one units? Several other manufactures are now following UK pioneers Exposure down the all-in-one route rather than using a separate battery and light. Mounting is easier and the whole setup much tidier, but larger capacity all-in-one lights aren’t helmet-compatible. They’re also less upgradeable in the long-term than the most versatile modular systems.

Reliability: Mixing delicate electronics, extreme operating temperatures, powerful batteries, mud, rain and regular crashes isn't easy. Yet reliability is absolutely vital, because light failure at speed on technical terrain is no joke. The great news is that most lights available now are reassuringly reliable. If something does go wrong though, a well-established company is generally a lot easier and quicker to deal with than a foreign internet seller.

Light output is measured in lumens. This is usually a theoretical best though, and often doesn’t account for lens design or beam spread, which are highly important in how much useful light is kicked onto the trail

Features of a mountain bike light

Lamp body (head unit): This houses the LEDs, the lens in front, the reflectors behind, the circuitry that makes it all work and the fins or ribs that radiate away as much heat as possible.

LEDs: Most lights now use LEDs (light emitting diodes), because they produce more light for less power than a conventional bulb and are far less fragile than HID lamps. Technological advances mean performance has leapt forward in the past few years and each new season brings significant upgrades.

Optics: The reflector and lens in front affect how the light is thrown down the trail. Focused spot beams are great for seeing a long way for a given output; wide flood beams give good peripheral vision.

Mount/bracket: How you attach the light to your bike.Most mounts use clips and spacers but O-rings are a great simple solution. If you are thinking of using a helmet mounted light, you need a lamp that’s light enough to be comfortable and secure on your lid, rather than a neck snapper. You’ll need an extension cable and helmet mount too, so check if that’s included or an optional extra.

Battery: The bit that powers the light. Lighter, tougher, far more random charge resistant lithium ion (Li-Ion) chargeable batteries have revolutionised mountain bike lighting compared with older lead acid and NiMH batteries – but battery and lamp efficiencies still vary dramatically. Most brands sell extra batteries (often at a discount if bought with the light) so you can always swap halfway. Check your batteries are properly prepared for maximum performance (this should be in the instructions) and take a back-up until you know you can rely on their run times.

Switchgear: The switch not only turns the light on, but also lets you change power output levels. It needs to be easy to operate while riding, even with gloves on, but hard to operate accidentally. Many lights now use backlit switches that double as mode and/or run time indicators using traffic-light-style colour changes. Switchgears now range from a simple push button sequential mode switch with low battery warning light to wireless bar-mounted units or switches that can also change the different output levels and menus.

Charger: The most easily forgotten part of the lights package. Chargers range from USB leads to a plug with a lead on that lights up green when it’s done, to LCD-screened smart chargers or even battery docking stations that let you change lighting options via your PC. Car chargers are great for 24-hour races. Most chargers now use smart circuits for a fast initial charge that slows to a trickle so they don’t damage the battery, but actual charging speeds can vary quite dramatically. This can be important if you’re the sort of rider who forgets their battery is flat until an hour before a ride.

Leads: There are increasing numbers of all-in-one light systems, but most sets still use a head unit attached to the battery by a lead. Leads are often overlooked but vital to overall reliability. You want secure connectors that don't fall out and joining sections that won't let water or muck in and are long enough to fit your bike. Every joint wastes power, so it makes sense to keep things simple.

Head or bars

Most lights come with both bars and helmet mounting options. Which is better comes down to personal preference, but here are the pros and cons of each.

Helmet

  • √ Light shines where you’re looking
  • x Flattens out visible trail features, reduces depth perception
  • x Can be knocked off by low trees

Bar

  • √ Easy to see indicators and operate switches
  • x Light only goes where your bars are pointed
  • x Drops backside of crests and lumps into shade, so you can’t judge obstacle size

Pair a helmet spot with a bar-mounted flood and you'll generally have the best of both worlds

The result – It’s a draw! In reality the best solution is to use helmet and bar-mounted lights, even if you have to buy lower powered units to afford both. It also means you have a backup should one battery die.

Jargon buster

  • Amp-hour - A measurement of battery capacity. The bigger the capacity, the longer your lights will run. You need to divide this value by the amperage the light operates at in order to get the theoretical run time.
  • Bag - A cloth pack that holds the battery onto the bike's frame.
  • Bar mount - Light bracket that fits around oversize (31.8mm) and/or older 1in (25.4mm) diameter handlebars.
  • Battery cell - The single units that wire together to create a battery pack.
  • Bottle - Plastic water bottle converted to hold a large capacity battery.
  • Candlepower - Unit of light measurement.
  • Cell - Individual unit within a larger battery block. Most mountain bike light batteries are twin or quad cell units.
  • Colour temperature - Colour of the light. The more blue-white, the ‘colder’ the colour; the more yellow, the ‘warmer'
  • Cree - Leading LED manufacturer.
  • Flood - Head unit designed specifically to spread light over a wide area.
  • GoPro mount - Double-D and thumbscrew setup used on GoPro’s helmet cameras
  • Halo - A distinctive ring in the pattern of the beam.
  • Halogen - Best of the conventional bulb types. Cheap and easy to replace, but power-hungry so needs big, heavy batteries. Most manufacturers now use LEDs instead.
  • Helmet mount - Bracket that lets you fit the light on your lid.
  • HID (high intensity discharge) - A metal halide lamp that uses a tiny but extremely bright striplight bulb that only draws 10W but produces more light than a 40W halogen bulb. Gives that distinctive blue/white alien light of BMW headlamps. Most manufacturers now use LEDs instead.
  • Jack - Connector plug on the lead.
  • Jubilee clip - Fastener that uses a band tightened with a screw-driven gear wheel.
  • LED - Light emitting diode. A solid state semi-conductor that glows brightly when a current is passed through it. The 'bulb' choice of most manufacturers.
  • Lead - Cable that connects the head unit and battery. Extra long extension units are available for use with helmet mounts.
  • Lens - The screen over the LED and reflector that protects them and can also be used to modify the beam.
  • Life indicator - Traffic light style colour change display that indicates the remaining charge in a battery.
  • Li-ion - Lithium Ion. The most expensive but lightest, most efficient battery available. Also the easiest to look after in terms of charging/ recharging and therefore a very good thing.
  • Lumen - Often quoted measure of the theoretical power of a light. Thermal issues and management circuitry normally make it an optimistic guide at best, though. With no standard way to measure it for bike lights, most figures can't be usefully compared.
  • Lux - Lumens per square metre. The real light output figure that we generally use in our comparative lab tests.
  • NiMH - Nickel metal hydride. Cheaper battery type that's reasonably robust in a charge/recharge sense but heavier and bulkier than a Li-Ion for the same capacity.
  • O-ring - Thick rubber band used in some handlebar mounts.
  • Peripheral - The outward edges of the field of vision. Useful for seeing movement in low light.
  • QR - Quick release mechanism.
  • Reach - The distance down the trail that the light illuminates.
  • Reflector - The shaped reflective surface behind the LED that concentrates and reflects the beam of light.
  • Seoul - LED manufacturer.
  • Smart charger - Charger that senses how full/empty the battery is and adjusts its efforts accordingly rather than burning down your house.
  • Spot - Head unit designed to focus light in a narrow, long reaching beam.
  • Throw - How far a light's beam can reach in front of it.
  • USB - Universal serial bus. Standard connector for computers.
  • Voltage - The power level the battery releases its energy at.
  • Watt - A measurement of power. You'll often see bike light outputs quoted as 'equivalent to a 20W halogen bulb' for example.

How we test mountain bike lights

Being stuck on a wet winter’s night, miles from anywhere with a failed light or everything suddenly going pitch black halfway down a technical descent is a really serious matter. That’s why we take our lights testing extremely seriously.

For all the calibrated data on max power run times, lux ratings, light spreads and ranges we can get in the workshop, what really matters is the test feedback we get on the trails: which brackets continually loosen or which leads fall out; which batteries bounce about, scratch paint or are a right pain to fit on different bikes; which drown in downpours.

There’s no substitute for time on trail in all weathers to find out this crucial stuff – and we’re not just talking about the past few months with these lights either. We also reference the sets we’ve run continually since last year to get in-depth, long-term, worst case use feedback that’s directly relevant to the riding you do.

We test lights out on the trail and in the workshop, and any failings soon show up

The science side

As is often the case with mountain biking, the scientific part of the testing is the easiest bit. Lights (lamp body plus handlebar bracket) and batteries are weighed on our scales.

We then measure the useful maximum power run time (to when the output fades and low battery warning lights come on) with pre-conditioned (used and recharged) batteries in the highest power setting on an aircooled rig to mimic the cooling effect of riding at night. We also measure the maximum casing heat of the lights with a thermal probe to see if any get dangerously hot.

Light output is calculated using a lux (a measurement of one lumen per square metre) calibrated industrial light meter placed 5m from the lamp in a blacked out workshop. (If the light has more than one beam or head unit we measure both separately and their combined output.)

This method does favour spot beams over flood beams, but it’s still a more trail translatable measurement than the lumen potential of LEDs. The coverage, density and other specific characteristics of the beam are often more important than the peak brightness though, so we also take beam photos to make it easier to compare the lights.

The practical side

It’s the feedback we get from real world usage that really sorts out often very similar lamps in terms of trail performance. The reason I get to do lights testing up north most years isn’t because I’m a modern Edison – it’s because our local test crew put in more hardcore nocturnal hours on their bikes than any other group I know.

We’re talking serious sorties, often two or three times a week all year round in every trail condition imaginable. Baked hard river bed runs that’ll shake a poor bracket or fragile circuit board apart in seconds or leave a badly bagged battery hanging by its lead; sub-zero tundra trudges that freeze a battery to horribly low maximum power run times; drownings in downpours and hip-deep bog crashes.

Most of our lights have seen it all and, if the most recent versions have only been hammered through summer, we’ve certainly put the models preceding them through the most testing ride schedule possible. Repeated group riding, bike switching, recharging and battery flattening gives us the perfect comparative testing cluster too, so any failures or fading is immediately obvious rather than going unnoticed in isolation.

In other words, if a light scores well, you know it’s gone through some proper optical and electrical purgatory to prove itself. For that reason, for our latest round of lights testing we’ve deliberately stuck with established (at least a year old) lights manufacturers to ensure anything we recommend is a fully supported product.

Light output is calculated using a lux calibrated industrial light meter

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