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.
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:
- Lumos Firefly: 38 lumens (84 lumens with the brake lights), 48 lumens for turn signals
- "M" Light: 90 lumens
- "L" Light: 75 lumens
- "S" Light: 60 lumens
- "C" Light: 90 lumens
- "K" Light: 50 lumens
- "A" Light: 45 lumens
(L to R) Lumos Firefly, "M", "L", "S", "C", "K", "A"