Reviews You Can Rely On

How We Tested Bike Lights

Monday January 15, 2018

As you explore the myriad of bike light options available, you can easily get lost in a sea of competing products, each boasting self-reported performance specifications that are often unreliable, and in some cases are even deceptive, which is why we prefer to put their claims to the test. Please refer to our article Why Headlamp Claims Are Deceptive, for more information on this topic.

Testing Methodology

We created our very own bike light testing standards to address this issue. Here are the key elements in our testing philosophy:
  • Do not rely on manufacturers' claims.
  • Test all the finalist products ourselves, hands-on, and in a consistent manner.
  • Perform field tests as well as lab tests to assure fair and objective ratings.
  • Field tests include trail/path finding tests, address/sign location tests around neighborhoods, gloved tests, and ease of use tests.
  • Test brightness levels with industrial light meters, measured in the same way for every product.
  • Provide photos of beam distance and beam diameter in spot and close proximity mode.
  • Provide graphs of battery run-time performance degradation using our proprietary "light coffin" which measures brightness each minute with a data logging light meter, to reveal how beam distance degrades as batteries get weaker.

This is the industrial light meter we used for our brightness tests
This is the industrial light meter we used for our brightness tests
Photo: OutdoorGearLab

Beam Distance Testing

We measured each bike light's maximum brightness using the same industrial light meter (Extech LT300) in units of lux measured at a distance of four meters. All tests were conducted in a controlled environment to eliminate variance due to changing temperature and humidity levels. In each test, we fully charged each light or used fresh alkaline batteries from the same battery manufacturer (Energizer Alkaline AA and AAA batteries in our tests), and brightness was measured one minute after turning on each light with these fresh, fully charged batteries.

To convert these brightness measurements to beam distance, we used a similar calculation method as described on the Black Diamond website in 2010 used to make headlamp calculations, which we also did, initially; however, our calculation differed very slightly since we measured Lux at four meters distance instead of two meters.

Below is an excerpt from an article on the Black Diamond website blog in 2010:
BD crew
30 Mar 2010, 1:31PM

…Our distance measurements are calculated by determining the maximum "lux" level at two meters. We then use the inverse proportion law (rule) to extrapolate the distance the light beam will provide a 0.25 lux measurement. This 0.25 lux is the equivalent of the amount of light that is produced by a full moon on a clear night, which is a light level most people have experienced. The distance measurements and the manner in which we calculate them are the standard followed by all major headlamp and lantern manufacturers. Black Diamond also calculates battery life (burn-time) by running the headlamp or lantern until a light level of 0.25 lux at two meters is reached.

If you really care, here is the math for distance calculation:

E=i/(D²). [The D² is D "squared"]

E is the illuminance in "lux", "i" is the luminous intensity (in candela) and D is the distance in meters, from which the measurement was taken.

We measure an Icon [2010] headlamp to read 651 lux at 2 meters. Therefore the luminous intensity is: 651=i/(2²) or i=651 x 4 = 2604 candela. [Again, the i/(2²) is actually 2 squared]

To calculate the distance the light beam will read 0.25 lux, we substitute these values into the equation:

0.25 = 2604 / D² or D² = 2604 / 0.25 or D = (10,416)-2 D = 102.05 meters. [One more time, D² is D squared]

There will a quiz on this tomorrow.

Being skeptics by nature, we were unwilling to use this calculation based on brightness to determine beam distance until we could verify the math worked in practice. To do so, we walked out into an empty field with our light meter on a moonless night and tested a handful of headlamps manually to be sure the predicted beam distance based on our measurements at four meters distance matched what we observed in the field. It did!

Battery Run-Time Tests

This light is a great option for urban commuting, with some great...
This light is a great option for urban commuting, with some great features that help oncoming traffic see you.
Photo: Gentrye Houghton

To measure battery run-time, we built a light-proof box we call the OutdoorGearLab Light Coffin which is instrumented with a data logging light meter. Now, each bike light is placed at a fixed distance from the light meter, which is in turn connected to a laptop to record the data. We close the box and begin measurement one minute after the light is turned on. This setup allows us to measure brightness once a minute and see how performance degrades as the batteries drain. Using similar math as described above, we then convert the recorded data into a visual graph of beam distance over time (see below).

The above light is spec'ed for a 75 meter distance and 50 hour...
The above light is spec'ed for a 75 meter distance and 50 hour run-time. We measured beam distance at 70 meters, a bit less than claimed, but we found run-time to be 5.2 hours using the ANSI FL-1 standard, 90% less than the claimed battery life.
Photo: OutdoorGearLab

The data from our Light Coffin tests also allows us to determine battery run-time as defined by the American National Standards Institute protocol (ANSI) FL1 Flashlight basic performance standard.

The ANSI FL1 standard calls for battery run-time duration to last until the brightness level diminishes to 10% of the initial maximum value. As noted in our accompanying article, Why Headlamp Claims Are Deceptive, the manufacturers have refused to use the ANSI FL1 standard for battery run-time (that they helped develop) and instead use their own alternative method, which we believe vastly overstates battery run-time. We think you'll get a better picture of how lights compare in battery run-time by relying on our test results.

Field Testing

The most fun part of this review is getting to use all these different bike lights out in the field over a 6+ month testing period. We performed trail/path finding tests, address/sign location tests around neighborhoods, gloved tests for ease of use and portability tests. We donned lights on our heads, helmets, and handlebars using them on dusty trails, around town, and in dimly lit rural areas. Field test ratings involve a subjective judgement of performance, and to increase reliability, we deployed a team of reviewers to score each light objectively in these different hands-on test scenarios.

Beam Photos

To help you see how each bike light compares to one another, we took photos of each light shining down the same bike path on a moonless night. These photos allow you to see the relative performance of each beam for yourself.

Beam Distance Photos
Beam photo of NiteRider Lumina 750
Beam photo of Light and Motion Urban 350

NiteRider Lumina 750
Light and Motion Urban 350

In addition, we took photos of the beam diameter pattern in the high mode of the light. These photos allow you see if there are aberrations in the light pattern, as well as the relative beam width. These photos were taken with the light one meter from the target screen. The scale on the screen is in centimeters. Camera settings were fixed for each type of photo test.

Weight Comparison

Rather than rely on manufacturers' weight measurements, we measured the weight of each product on the same scale, with batteries installed.

Interpreting the data from our light coffin.
Interpreting the data from our light coffin.
Photo: OutdoorGearLab Staff