Guide · Lights
Lumens, lux and candela: what a bike light's numbers measure
Lumens are total output, lux is light landing at a stated distance, candela is intensity in one direction. How to read each figure on a bike light.
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Short answer
Lumens are a light's total output. Lux is how much of that light lands on a surface at a stated distance. Candela is intensity in one direction. A lux figure without its distance tells you very little, and none of the three tells you on its own how well a light shows the road.
Three units, three questions
The candela is the SI base unit of luminous intensity, and the lumen, the unit of total luminous flux, is derived from it.[1] In plain terms:
- Lumens answer "how much light comes out in total?"
- Candela answers "how intense is the light in one direction?" It is the figure for the brightest part of a beam.
- Lux answers "how much light lands on this spot?" One lux is one lumen spread over one square meter.
The catch with lux is distance. For a point source, illuminance falls with the square of the distance.[2] Double the distance and the lux reading drops to roughly a quarter. A lux number is only meaningful next to the distance it was taken at.
| Unit | What it measures | Where you see it on bike lights |
|---|---|---|
| Lumen (lm) | Total light output | Most rechargeable lights' headline figure |
| Lux (lx) | Light landing on a surface at a set distance | German StVZO dynamo lights, some reviews' meter readings |
| Candela (cd) | Intensity in one direction | Flashlight-style spec sheets under FL 1 |
How ANSI FL 1 reports beam numbers
ANSI/PLATO FL 1 is a portable-light performance standard that some makers follow. Under it, beam distance is the distance at which the beam falls to 0.25 lux, and peak beam intensity is reported in candela.[3] That 0.25 lux point is a faint glow, so a long "beam distance" is not the distance at which you can read the road. Following FL 1 is voluntary, and each company runs its own tests.[3]
Where lux numbers come from
Reviewers who publish lux readings use their own setups. road.cc measures lux 2 m from each light, taking 11 readings in 10 cm steps from the beam center out to 1 m.[4] That shows how the light spreads across a small target, not how far it reaches.
BikeRadar's 2021 Ravemen CR1000 review lists 142 lux at 5 m on high beam in its features box.[5] The review does not say whether that figure was measured or copied from the maker's specifications, so treat it as a listed figure, not a BikeRadar measurement. It also cannot be set beside a road.cc reading taken at 2 m.
Lights rated in lux: StVZO dynamo lights
Busch + Müller lists its IQ-X dynamo headlight at 100 lux low beam, StVZO approved, running on a 6 V AC dynamo supply at 2.4 W.[6] StVZO is a German approval. It says nothing about the rules where you ride in the US or Canada. Our guide to cutoff beams and StVZO lights covers what that approval involves.
Lights rated in lumens: maker examples
These are the makers' own ratings, not measurements:
- Magicshine rates the EVO 1700 at 1,700 lumens on high beam.[7]
- Ravemen describes the CR1000 as a 1,000-lumen front light.[8]
- Fenix rates the BC25R at 600 lumens maximum.[9]
- Knog rates the Blinder 1400 at 1,350 lumens in High Steady.[10]
A higher lumen figure means more total light, not a better beam. A light with a cut-off beam can put more of a smaller total on the road; a round beam can spend part of a larger total above the horizon. Compare beam photos taken on the same setup before you compare totals.
Picks that fit2 products
Knog Blinder 1400: choose the light-only version; Knog rates it at 1,350 lumens in High Steady and lists a 22.2-35 mm bar mount.
More on choosing
Magicshine EVO 1300: an under-mounted front light, a different model from the EVO 1700 above, so read Magicshine's own page for its ratings. On Amazon, check that 'Ships from / Sold by' shows Amazon.com or the brand.
Front light with runtime by steady mode
Under-bar front light with runtime by beam mode
Magicshine EVO 1300 under-mount front light (cut-off low beam, USB-C)
How many lumens for commuting?
We found no source that sets a lumen number for commuting. A lit city route and an unlit country lane ask different things of a light, and the beam's shape decides how much of the output lands where you need it. Pick by the mode you will actually use and by beam photos from one reviewer's setup, then check its runtime in that mode.
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Questions
Is lux or lumens better for comparing bike lights?
Neither is better; they measure different things. Lumens describe the light's total output, while lux describes how much light lands on a surface at one distance, so a lux figure is only useful with its distance.[1][2]
How many lumens do I need for commuting?
We found no source that sets a lumen number for commuting. Your route, street lighting and the beam's shape matter as much as the total, so compare beam photos and the modes you will actually use.
Why do German bike lights list lux instead of lumens?
Busch + Müller, for example, rates its StVZO-approved IQ-X dynamo light at 100 lux low beam rather than in lumens. Lux describes light landing on the road ahead, but we found no source that states why German makers prefer it.[6]
Can I compare lux figures from two different reviews?
Only when both were taken at the same distance with the same setup. Illuminance falls with the square of distance, and road.cc says even its own beam photos compare only within one year's test.[2][4]
What does beam distance on a light's box mean?
Under ANSI/PLATO FL 1, beam distance is the distance at which the beam falls to 0.25 lux. It says how far a faint glow reaches, not how far you can see clearly.[3]