Why 'Lumens' is not the absolute standard when comparing lights

Lumens does not equate to brightness

'Lumens' is not the be-all, end-all when comparing brightness between lights. We'll prove it.

Hello again! As most of you may know, we're in the midst of launching our first ever smart bike light, and it just clicked that most people only had one question in mind - How many lumens does the Firefly have? If you've noticed, we didn't talk about our lumen rating in our previous Co-Creation series, as we didn't believe that a high lumen rating equates to a high level of brightness. Let us explain.

What do we typically look for when shopping for any type of lights? Lumens, Candela, Lux. These are the 3 typical ways to measure how 'bright' a light can be. Most bike and torch lights use 1 of the 3 metrics more often than others, but before we jump into that, let's understand what each of these measurements means.

Starting with the easier definitions:

  • Candela measures how bright a light is in one specific direction, like how far a flashlight can shine.
  • Lux is how bright a light is on a surface, like how bright a room is.
  • Lumens measure how much light comes out of a light source in all directions, like the total brightness of a lightbulb.

For those of you who'd like a bit more of a detailed/ geeky explanation:

Candela measures absolute brightness at a point. In other words, it measures the amount of brightness going in only one specific direction. This unit is sometimes used to define maximum brightness of a light. The value for candelas is the same regardless of distance from the light, but will be different depending on the angle from the light.

Lumens measure total luminous flux, in other words the total output of a light source in all directions that it points. If you were to integrate the candelas measured in every direction around a light source, you would get lumens. Lumens are measured using an integrating sphere, a scientific instrument that uses a reflective sphere to normalize the light beam and measure its intensity.

Lux is lumens per area. If you project a light onto a surface and add up the total amount of light hitting it and divide by the area of the surface, you get lux. The brightness in lux depends on the distance at which you measure it. Illuminance is inversely proportional to the square of the distance, so in order for lux to be a useful measurement you must know the distance at which it was measured.

Let's get back to bike/ running lights

We know that the primary use of bike lights is to help us see, and to be seen. More often than not, being seen greatly reduces the chances of another road user coming too close to you. So which primary light unit do these lights use? 

'Lumens' have been found to be the most common measurement, and consumers tend to associate a higher lumen value with higher 'brightness'. Sure, 1 lumen is definitely brighter than 0 lumens, but that's not the same when comparing 100 lumens vs 50 lumens. 

Let's show you why this holds true.  

We ran a mini test between our first ever smart bike light, the Lumos Firefly, against products within the similar category. Excuse the simplicity of the test, but we think it's a good indication to help you better understand why Lumens do not equate to brightness levels.  

These were the products included in the video, along with their stated product lumens. A big caveat here is that the lights were all set to 'Constantly On', which may be dimmer than other settings. In our case, Lumos Firefly's brightness levels are customised via our Lumos App, and we've set it to the highest brightness settings with the reported values below.  

In order from left to right:

  1. Lumos Firefly: 38 lumens (84 lumens with the brake lights), 48 lumens for turn signals
  2. "M" Light: 90 lumens
  3. "L" Light: 75 lumens
  4. "S" Light: 60 lumens  
  5. "C" Light: 90 lumens  
  6. "K" Light: 50 lumens
  7. "A" Light: 45 lumens

(L to R) Lumos Firefly, "M", "L", "S", "C", "K", "A"

As you can see, despite some lights having a > 2x higher lumens rating, the Lumos Firefly in its default rear light mode (38 lumens) fares comparably well, arguably better, against other light products with higher lumen values. In its turn signal mode (48 lumens), it is already visibly brighter than most, if not, all other lights, despite having a lower lumens rating than all other products. That goes without saying, the brake lights of the Lumos Firefly looked at least twice as bright as other lights.

So what does this mean?

We're not claiming that the Lumos Firefly is better than other lights (that may be what we think, but it ultimately depends on the type of ride you're on, your preferred build for the design, or perhaps if you want a light that isn't too bright). This just goes to prove our point that 'lumens', despite it being the single most popular metric in assessing brightness levels, are not the 'be all, end all' when comparing brightness levels. 

Lumos is focused on ensuring riders are visible, and can communicate their intentions through turn signals and brake lights, just like any other car or motorbike on the road - and that's why 'visibility' and 'communication' remain as our most important metrics, instead of purely relying on lumens as a rating.

You can start your journey in moving smart, and staying safe, by ordering a set of your own Lumos Firefly lights here.

1 comment

Appropriate explanation, thanks.

WT HUFF November 22, 2023

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