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How Many Lumens Do I Need for Mountain Biking at Night?

It’s a question we hear from Singletracks readers all the time: How bright does my light need to be for mountain biking at night? As always, the answer depends on a number of factors. The conventional wisdom says the brighter the light, the faster the rider can navigate the trail, but is this true? How much faster can a rider go with a brighter light?

The set-up

The Light & Motion Trail 1000 FC Ranger pumps out up to 1,000 lumens and includes a helmet mount in the box.

Obviously this test occurred at night, in the dark, on a singletrack trail. The test loop itself has a little bit of everything: twisty sections, techy bits, wide open areas, climbs, and descents. Mike and Paul were our test riders, and they took between 3 minutes, 16 seconds and 4 minutes, 2 seconds to ride the approximately half mile loop.

We hypothesized the riders would get slightly more tired after each lap, which could cause them to slow down, regardless of the light configuration. However, we also guessed the riders’ speeds might increase a bit as they became more familiar with the course. It was possible these two would cancel each other out, but it was also possible one effect would be greater than the other.

So, we randomized the trial, and also threw in a lap where nothing changed; that is, the rider kept the same light setting from one lap to the next. It turns out Paul got about 5% faster from one lap to the next, so knowing the course won out over fatigue, at least for Paul.

Both Mike and Paul ran the lights on their helmets for each test, and each used different lights which accounts for the various maximum and minimum lumen counts on the chart.

The Light & Motion Trail FC 1000 Ranger is a “fast charge” model which is great for those who wait until the last minute to charge their lights. It offers 4 light modes and weighs 121g, perfect for helmet mounting.

The results

Looking at the chart above, Paul’s dots are red while Mike is shown in blue and green. (Mike tested two different lights with slightly different maximum and minimum brightness settings.)

Paul’s test

Paul’s test results ended up being the most consistent, showing a steady increase in speed as brightness increased from 300 lumens all the way up to 1600 lumens. Doubling brightness from 300 lumens to 600 lumens resulted in a nice 6.6% bump in speed. A second doubling, from 600 lumens to 1200 lumens, resulted in an even bigger increase in speed, which could indicate a non-linear increase in this zone.

It’s interesting to note that Paul’s times seem to plateau once he hit 1200 lumens on the helmet light. That is, he didn’t get much faster going from 1200 lumens to 1600 lumens. There are two possible explanations here.

First, once a rider has “enough” light, additional light doesn’t help as much. This is the rule of diminishing returns, which seems fairly plausible. Riders only need to see so far down the trail, and beyond a certain distance, trees and obstacles tend to block trail views whether it’s day or night.

Secondly, Paul’s 1200 lumen run was his last, which means he was more familiar with the course on this run than on his 1600 lumen run. So, it’s possible the 1200 lumen run might have been a little slower if we were able to normalize the times somehow, leading to a more linear result.

Mike’s test(s)

Mike actually tested two separate lights over the course of 5 laps, and his results were a bit mixed. For the “blue dot” light, the results were as expected. At 800 lumens, Mike rode about 5.5% faster than he did at 200 lumens. That’s a big jump in brightness, so it’s surprising he wasn’t much faster than that. Add in the fact that the brighter light came during a later lap, and that gain is even smaller. But, it’s still a gain.

For the “green dot” light test, Mike’s results are puzzling. He actually got slower the brighter the light was set! How is this possible? I have a few theories.

Mike completed his first lap with the light on high (1,000 lumens), when his knowledge of the course was at its worst. All else being equal, we expect riders to get faster with each lap as they learn the course. Still, this doesn’t explain why his third lap, at 500 lumens, was slower than his second lap at 250 lumens.

Mike was the most consistent in terms of his speed overall, with a spread of just 16 seconds between his fastest and slowest laps. (Compare that to Paul, whose spread was 46 seconds.) It’s possible something else, other than the brightness of the light — like stamina or even the fact he was riding a rigid mountain bike — limited his speed, more so than the brightness of the light.

The 250 lumen test lap seems suspiciously fast, for reasons unknown. This lap was 9 seconds faster than his 200 lumen lap, despite a negligible bump of just 50 lumens. A timing error or even a course shortcut could have been at play.

Conclusion

Admittedly the results aren’t decisive, but we did gain some key takeaways about mountain biking at night.

  • Brighter lights allow riders to go faster. It’s unclear whether there is a linear relationship between brightness and speed, but in four out of six cases (66% of the time), the rider was faster with a brighter light.
  • There are diminishing returns to brightness. Paul’s test results show this, and Mike’s results hint at a similar conclusion. In any event, there does seem to be a limit to the improvement riders will see to running a bright light, though it’s unknown where the sweet spot lies, or if it varies from rider to rider. However, it’s safe to say a 6,000 lumen light won’t allow riders to go six times faster than a 1,000 lumen light. Consumers don’t need to spend a lot of money on the brightest light on the market, and can instead focus on other factors like durability, battery life, beam pattern, etc.
  • Knowing the trail increases night-riding speed. Of course this is true in the daytime as well. So if night riding feels slow, riders should be able to improve by simply riding the same trail at night more often.

While Light & Motion agreed to sponsor our test, they didn’t influence the results in any way, and this isn’t meant to be a ploy to sell you on a brighter light. If you’re skeptical, by all means, run your own test and let us know what you learn!

Your turn: Have you found a sweet spot in terms of light brightness for trail riding? If so, how many lumens are “enough” for you?

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