Currently, I'm using a front light rated at 35 lux on my bike. This is just about bright enough for my riding, but I'd like something a bit brighter. However, most of the lights which might be brighter are rated in lumens, rather than lux.

I'm a physicist by training, so I know the difference between 1 lux and 1 lumen and that you can't compare them directly - but that doesn't help me as I do need to compare them somehow. Is there any rule of thumb or something that I can use to work out which lights are actually brighter than my current light, or does the beam pattern of lights vary too much for this to be a sensible comparision in any way at all?

  • Interesting. Does the manufacturer have specifications on what angle/height to mount that light to get the proper output? It seems like lux would vary based on mount angle and bar height, where lumens would be a better standard for comparsion. Although you are correct beam width varies and the comparison is hard anyway. Commented Dec 1, 2014 at 22:25
  • I also came across Candela when I looked at this a few years back. But yes, I think various assumptions have to be made before you're in a position to compare.
    – PeteH
    Commented Dec 1, 2014 at 22:32
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    For everybody else that isn't familiar with the units: lux is how brightly lit a surface is, candela is (usually) the brightness of the center of the beam, and lumens is the total light output. Candela can be converted to lux (and vice-versa) given a distance. Lumens can be converted to candela (and vice-versa) given degrees (how much of the sphere the light comes out), but most bike lights spread light unevenly.
    – freiheit
    Commented Dec 1, 2014 at 23:26
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    @PhilipKendall how many LEDs in that light? Smart Lunar rebrands lights from other companies for sale in different markets, especially in Europe. They particularly sell a lot of Planet Bike and Portland Design Works lights under their brand. It looks like it's probably either the Planet Bike Beamer 5 or the Planet Bike Blaze 2w Micro. Interestingly, the Beamer 5 is claimed to put out 35 lumens... I wonder if when they rebranded it they just said "eh, lumens, lux, what's the diff" and called it a 35 lux light.
    – nhinkle
    Commented Dec 2, 2014 at 0:27
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    @nhinkle Ah, that's really useful information. It's actually the Blaze 2w Micro and therefore 139 lumens. That's also pretty much consistent with the diagram from Smart's 700 lumen light on Amazon which gives an equivalence of 35 lux to 121 lumen. Feel free to post all that as an answer :-) Commented Dec 2, 2014 at 8:40

5 Answers 5


I don't think you're going to be able to do any reasonable conversion, since lux without a distance is meaningless. It's likely that the manufacturer has picked lux specifically to make it sound impressive, or possibly even to make it hard to compare.

Here's a nice description of the (optional) standard: http://www.led-resource.com/ansi-fl1-standard/. One of the possible measures in that standard is the distance at which the light is 0.25 lux. Another is the candela (peak beam intensity). And, of course, there's always lumens (total output). Lumens seem to be the favorite.

Instead of trying to compare the brightness of your current light, I recommend visiting this great light comparison site (which originally started from some posts on our blog): https://www.bikelightdatabase.com/

In particular, the beamshot photos on that site are super-useful. There can be big differences between lights that use the same measurement (usually lumens) and being able to look at what that looks like on a stretch of road is amazingly helpful.

  • Indeed. A lot of manufacturers (esp. cheaper ones) often lie about whats produced and what not, so to compare lights you often have to look at reviews with beam patterns (of which Nathan's site (bikelightdatabase) is a fantastic resource).
    – Batman
    Commented Dec 2, 2014 at 0:05
  • Thanks for the support guys! There's also some info on the FAQ about lumens vs. lux and other measurements. That section is going to be getting a rewrite soon with a lot more detail.
    – nhinkle
    Commented Dec 2, 2014 at 0:18

Assuming it is intended to throw a 1 m^2 patch in front of your bike suggests it may be a ~35 lumen or so light. I think you'd be safe in looking for 100 lumen (or greater) light to replace with. Looking at that price range, I'd think those were reasonable assumptions to make. Unfortunately, without knowing how large a patch it it intending to throw, you'll never be able to make a direct comparison.


[ All credit for this answer goes to nhinkle, hence the community wiki ]

In this specific case, it's actually fairly easy. The light which you've linked to, the Smart Lunar 35 lux, is actually just a rebranded Planet Bike Blaze 2W Micro which has a claimed 139 lumens. (A number of Smart products are actually just rebranded from other manufacturers, particularly Planet Bike and Portland Design Works).

As others have commented, there's not a general way of doing this and you're probably best off concentrating on reviews rather than technical specifications.


That is an inexpensive light that runs on 2 AA batteries. And has a narrow beam.

Rather than focus on getting something just a "little" brighter if you want to stay cheap just buy a second AA light and use both. Or get a second of the same.

Or step up to more expensive rechargeable lithium ion light. It will be brighter. Focus on reviews.


Best bet is to look at them - if you can't do it in person, look for reviews with pictures of the beam and illumination.

For example, road.cc have a comparison tool. I couldn't immediately see anything putting 35 lux in the centre, where I assume yours is measured.

The Topeak Whitelite HP Beamer (who names these things?) is closeish at about 30 lux, so maybe see if that looks similar to yours.

  • Lux is relative to distance. That graph is based on lux at 2 meters from the light. What distance is the light in the question getting 35 lux at?
    – freiheit
    Commented Dec 5, 2014 at 18:01
  • No clue. I've seen OP's light wearing a few different badges, and I was hoping the comparison would include one of the rebranded versions. Couldn't find one, but maybe OP knows that light well enough to tell roughly where it sits.
    – Useless
    Commented Dec 5, 2014 at 18:03

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