Bike Lights for Night Riding: Lumens Are the Wrong Spec

Two riders came the other way down a shared path last winter, both on e-bikes, both with headlights that had big numbers printed on the box. One I could see clearly from a hundred metres out and pass without slowing. The other blinded me so thoroughly I had to look at the ground and guess where the edge of the path was until he'd gone by.

The second one probably had the brighter light.

That's the whole problem with how bike lights get sold. The number on the packaging measures total light output, and total light output tells you almost nothing about whether you'll see the pothole or whether the driver turning left will see you. If you only take one thing from this: stop shopping by lumens.

Lumens are the least useful number on the box

A lumen is a measure of how much light a source emits in total, in every direction it emits. It says nothing about where that light lands. Two headlights rated identically can produce wildly different results — one spreading its output into a wide, even pool on the road in front of you, the other firing most of it into a tight circle that's dazzling in the middle and useless three metres to either side.

What you actually care about is illuminance: how much light arrives on the bit of ground you're about to ride over. That's measured in lux, and it depends on the optics, the aim, and the distance. A well-designed lamp with a modest lumen figure and a proper lens can put more usable light on the road at the distance that matters than a badly designed lamp with double the rating.

There's a second reason the number inflates. Nobody's obliged to state output the same way, so figures get quoted as raw emitter output, as measured output at the lens, as a peak reading in the first thirty seconds before the lamp thermally throttles, or as whatever marketing felt good about. A four-figure lumen claim from a brand with an engineering reputation and the same claim from an unbranded marketplace listing are not the same measurement.

Runtime claims have the same problem. "Six hours" nearly always means six hours on the lowest setting, which is the setting you'll never use. Look for runtime at the mode you'd actually ride in.

None of which means output is irrelevant. There's a floor. A lamp that's genuinely dim won't light an unlit road no matter how good its lens is. But past a certain point — roughly wherever a decent commuter lamp lands — extra lumens buy you very little, and beam quality buys you a lot.

Two lights, two completely different jobs

Being seen and seeing are separate engineering problems, and a lot of frustration comes from expecting one lamp to do both well.

Being seen means throwing enough light toward the eyes of people who might hit you, from as many angles as possible. It doesn't take much output. It takes visibility off-axis — to the sides, not just straight ahead — because the vehicle that's actually a threat is often approaching from a side street, at ninety degrees to where your light points.

Seeing means putting a shaped, even pool of light on the road surface a sensible distance ahead, with no bright hotspot to contract your pupils and no glare bouncing back at you off wet tarmac. This is the harder job and it's where cheap lamps fall apart.

On a lit city street, being seen is nearly the entire task — streetlights already handle the road surface. On an unlit rural lane or a canal towpath, seeing takes over completely. Most of us ride both in the same week, which argues for a lamp with a genuinely useful low mode rather than one enormous setting.

Beam pattern: the spec nobody advertises

Here's the distinction that separates a good headlight from an expensive flashlight strapped to a handlebar.

Round beams versus shaped beams

A torch-style lamp projects a circle. Point that circle at the road and the top half of it goes into the eyes of everyone in front of you, while the bottom half lands uselessly on your front wheel. Aim it down to stop dazzling people and your useful range collapses to a few metres.

A shaped beam — the kind with a horizontal cutoff at the top, like a car's dipped headlight — solves this by putting a hard edge on the top of the pattern. Light goes onto the road, out to a useful distance, spread wide enough to show you the kerb and the gutter. Almost nothing goes above the horizontal, so oncoming riders and drivers see a bright lamp without being blinded by it.

The German StVZO standard is the shorthand worth knowing. Lamps built to it are legally required to have that cutoff and a specified minimum illuminance, and manufacturers like Busch+Müller and Supernova have designed around it for decades. You don't need to live in Germany to benefit. "StVZO-approved" on a lamp is a reliable proxy for "someone designed the optics on purpose."

The trade-off is real: cutoff lamps tend to look less impressive in a shop, because the wall in front of you shows a wide bar rather than a searing dot. They also cost more, because a moulded lens is harder than a reflector cup. On a bike path with two-way traffic, they're not close to optional.

Side visibility, which almost nobody checks

Stand three metres to the side of your own headlight while it's on and look at it. If it disappears, so do you — to every driver at every junction you cross. Lamps with clear side windows, or a translucent body, keep working at that angle. Sealed opaque ones don't.

The collision geometry that hurts urban riders most isn't head-on. It's a vehicle emerging from or turning across your path from the side. A light that's invisible at ninety degrees is invisible in exactly the scenario you bought it for.

Aim, in one paragraph

Park facing a wall at about ten metres. The brightest part of your beam should sit low — well below your own eye height, and clearly below the eye height of an oncoming rider. If you have a cutoff lamp, the cutoff line should land on the road ahead, not up on the wall. This takes ninety seconds and it's the single highest-value adjustment on the bike. Most lamps come from the factory aimed too high, and heavier e-bike front ends with suspension shift aim over time.

Your rear light is doing the heavy lifting

If you had to pick one light to spend real money on, it's the rear one. Being hit from behind by a driver who never registered you is the failure mode with the least margin for recovery, and you're relying entirely on that lamp to prevent it.

Rear lights get treated as an afterthought — a cheap clip-on, half-dead battery, pointed at the sky. Meanwhile, the good ones have gotten genuinely clever. Some brake-sense automatically and flare on deceleration. Radar-integrated taillights like Garmin's Varia line detect approaching vehicles and change their pattern, which does two useful things at once. And plenty of ordinary lamps now have a proper wide-angle lens so you're visible to a driver in the next lane, not only to one directly behind.

The thing to avoid is a rear lamp so bright it's hostile. Extremely powerful taillights, especially strobing ones, can make it hard for a following driver to judge your distance and speed, which is the opposite of what you want. Bright enough to be unmissable, steady enough to be locatable.

Mount it where it can be seen. A seatpost is fine until you hang a saddlebag over it. Check it isn't blocked by a pannier, a rack deck, or a jacket tail — that's a mistake you can't spot while riding.

Should the front light flash?

This one is genuinely contested, and I'll give you my position: not on its own, and not on a shared path.

Flashing gets attention. It also destroys other people's ability to judge where you are and how fast you're closing, because a distance estimate needs continuous information. In a dense city with a lot of visual noise, a flash can pull a driver's eye toward you. On a dark towpath, it wrecks the night vision of every rider coming the other way and tells them nothing about your position.

The compromise that works: run a steady front lamp always, and add a flashing element only where you specifically want attention — daytime riding, heavy traffic, dusk. Some lamps offer a "pulse" mode that dims and brightens without going fully dark, which keeps the attention benefit and most of the positional information. That's the setting worth looking for.

Local rules matter here too. Some jurisdictions require a steady front lamp and treat flashing-only as non-compliant; others require flashing be paired with steady. It varies enough that guessing is pointless — check your own road traffic regulations, and check them for the vehicle class you're actually riding, since e-bikes and e-scooters are sometimes covered by different rules than bicycles.

Mounting, and why most setups aim at the wrong place

Handlebar mounting is the default and it's fine, with two caveats. On a bike with a bar bag or a phone mount, the lamp gets crowded out or shadowed. And a bar-mounted lamp sits high, which flattens the shadows on the road surface and makes potholes harder to read.

A lower mount — fork crown, front rack, or below the bars — gives longer shadows and more surface texture, so ruts and edges read as shapes rather than flat grey. It also keeps the bars clear.

Helmet lights are a supplement, never a primary. They point where you look — fantastic for reading a junction, terrible for oncoming traffic, since the beam sweeps across people's eyes every time you turn your head. Keep it modest and stay conscious of where you're aiming it.

One last thing: rubber-strap mounts are convenient and they creep. Check the aim occasionally, because a lamp rotated down ten degrees has lost most of its range.

Hub dynamos, integrated systems, and USB lights

E-bikes with integrated lighting run off the main battery, which is the right answer if your bike has it: nothing to charge, nothing to forget. The drawback is you're stuck with whatever lamp the manufacturer specified, and on cheaper builds that lamp is an afterthought. Many bikes let you swap the head unit while keeping the wiring — worth checking before you buy a battery lamp to sit next to a bad integrated one.

Dynamo hubs are still the best answer for anyone who rides in the dark constantly and hates charging things. Higher up-front cost, a little drag, and the light is simply always there.

USB-rechargeable battery lamps are what most people should buy, and the thing to check isn't output — it's whether the lamp warns you before it dies and what it does when it gets low. Good ones step down to a reserve mode. Bad ones go from bright to nothing with no warning, on a road with no streetlights.

Setup	Best for	Main compromise
Integrated e-bike lighting	Anyone whose bike already has it	Lamp quality is chosen for you; often a weak beam pattern
Dynamo hub + StVZO lamp	Daily year-round riders, tourers	Higher up-front cost, wheel build, slight drag
USB rechargeable, shaped beam	Most commuters and mixed-route riders	Remembering to charge it
USB rechargeable, round beam	Trails, unlit lanes with no oncoming traffic	Dazzles people; poor on shared paths
Helmet lamp	Second light for junctions and signs	Sweeps across other people's eyes; extra weight

The cheapest visibility upgrade you're not using

Retroreflective material on your moving parts — ankles, heels, pedal backs, crank arms — is disproportionately effective, and it costs almost nothing. The reason is that a human brain identifies another human by the rhythm of their movement long before it identifies a shape. Reflective dots that rise and fall in a pedalling cadence read unmistakably as "person on a bike." A static reflective panel on your back reads as "something."

Conspicuity researchers call this biomotion, and it's one of the few areas where the cheap intervention genuinely outperforms the expensive one. Reflective ankle bands cost less than a coffee.

The limit: reflective material only works when something shines light at it. It does nothing at dusk before headlights come on. An addition to active lighting, not a substitute.

How I'd actually spend the money

In order, if the budget is finite:

1. A good rear light with a wide-angle lens. Non-negotiable, and cheaper than the front.
2. A front lamp with a shaped cutoff beam from a brand that publishes real numbers. This is where the money goes.
3. Ankle bands or reflective pedal strips. Trivial cost, real benefit.
4. A second rear light in a different position and mode, because rear lights are the ones that get knocked off, covered by bags, and run flat.
5. Only then a helmet lamp, a radar taillight, or more output.

Things I'd skip: enormous lumen figures from unbranded sellers, front lights with no side visibility, anything with a proprietary mount you can't replace, and taillights bright enough to be a nuisance.

Questions people keep asking

How many lumens do I actually need?

Wrong question, but here's the useful version: on lit streets, enough to be conspicuous, which isn't much. On unlit roads at e-bike speeds, enough to see the surface at a distance you can stop within — which depends far more on how the beam is shaped than on the rating. Buy the best-shaped beam you can afford and the output tends to sort itself out.

Is one light enough, front and rear?

Legally, usually yes. Practically, a spare rear light is the cheapest insurance you'll ever buy, because rear lights fail silently — flat battery, knocked off at a rack, covered by a bag — and you have no way of knowing while you ride.

Do I need lights in the daytime?

A daytime rear mode is a cheap habit that seems to help, particularly in low sun, rain, or dappled shade where a rider blends into the background.

Will a bright light get me in trouble?

It can. Plenty of places have rules about dazzling other road users, and a badly aimed high-output round-beam lamp is exactly what those rules describe. Aim it properly and the question mostly disappears.

Are e-scooter light requirements the same as for bikes?

Often not. E-scooters are frequently regulated as their own vehicle class with their own lighting and reflector requirements, and the built-in deck light on many scooters wouldn't satisfy a bicycle standard either. Look up the rules for your specific vehicle class where you ride rather than assuming bike rules carry over.

What about the tiny light that came with my bike?

Treat it as a legal-compliance token, not a lighting system. It exists so the bike ships with lights. Ride an unlit road behind one once and the rest of this article will make sense.

If you do nothing else this week, take the ninety seconds to aim your existing front lamp against a wall. More riders are running a decent light badly than are running a bad light.