60, 90 or 150 … Lumen are not everything.
A bright head lamp is not always a good head lamp. There’s a few more factors to look at. The beam for example. A low Lumen headlamp with a good beam can be much brighter than a higher Lumen lamp with a poor beam. The actual brightness of a lamp is something subjective and very much depending on the design of the beam.
To better understand this topic, we need to know how Lumen are measured.
How do we measure Lumen?
In order to define the amount of Lumen, we need a device called an “Integrating Sphere” or “Ulbricht Sphere”. Never heard of it? Imagine a hollow ball with reflective inner walls and a light detector attached to the walls. The sphere can be opened and closed for putting a lamp inside. During measurement, the light of the lamp hits the inner walls and reflects into all directions – over and over again.
That ever reflecting light creates an even and diffuse brightness inside the sphere. No light can escape the sphere, so the brightness inside is a sum of absolutely all light coming out of the lamp. That evenly bright light is measured by the attached light detector and expressed in Lumen.
Integrating Sphere or “Ulbricht Sphere”
Well, sounds quite reasonable. It captures the sum of all light in one single measurement. Definitely great for light bulbs, because they are shining into all directions. But what does it tell about headlamps? Can it tell how good a headlamp is?
High Lumen are nothing without a good Beam
Now, we need to understand what headlamps are. They are mobile lights, producing light beams. Some beams are wide, some are narrow. Some are smooth, others are speckled with artifacts. Some have a wide corona, some have a precise edge.
The shape and the quality of a beam plays a major role for headlamps. The “Integrating Sphere” doesn’t take that into account. It only measures the total light coming out of the headlamps. But it doesn’t tell where the light is shining and how useful it is for our eyes and our vision. So let’s be a little bit careful with the Lumen. They are not everything!
Now, why can beams be so different? Because there are a million ways for manufacturers to produce a light beam. Some are rather simple, some are sophisticated. Some are cheap, others need a lot of engineering. So it’s up to the manufacturer whether he wants to spend a lot of effort, or just produce a cheap random spray of light.
A Good Beam gets the best out of your Eyes
Our eyes can adjust to very different conditions of light. To sunny daylight as well as to moon light. It’s quite impressive how good we actually see in low light. As long as our eyes had enough time to fully adjust. That’s when they work best.
Our eyes love constant conditions of light, not changing light. We know that from driving a car at night. When all of a sudden we get blinded by the head lights of other cars. Our eyes don’t “know” wether to adjust to the dark road or the bright lights. So they jump to somewhere in between. Not being able to use their full capabilities for the low light any more. As a result, the road in front appears darker as it would without the blinding.
What does that mean for our head lamp? Well, the beam of our own headlamp can be quite distracting too, keeping our eyes from giving their best. Many beams create an uneven scattered illumination in front of us, with darker and brighter areas, sometimes with reflections inside. Such artifacts can be quite irritating for the eyes. Especially over time or when we need to concentrate on our surroundings – like on a long mountain path. Our eyes get tired sooner as with a smooth spread of light.
A good beam is always gentle to the eyes. It supports our natural vision, so the eyes can use their full potential. A head lamp with good beam will always make us see better than a higher Lumen head lamp with a poor beam.
The beam above is a high quality beam with a smooth wide spread. No hot center which could distract our eyes or create too much reflection from objects.
Your Headlamp may be wasting Lumen
Yes, you may not get all the Lumen printed on the packaging. Many head lamps are wasting a part of their light in the areas around the center of the beam. Where the brightness of the center transits to the darker areas around. We’re saying they are wasting light, because our eyes may not be able to fully use the light in that area. Although it’s there.
In the image above, the beam has a very bright center with a harsh transition to the less bright areas around it. The difference in brightness may be too big. Forcing our eye’s to decide whether to adjust to the bright area in the center or the darker areas around.
Naturally, they will go with the bright area and close a bit. Meaning, they are not opened enough any more to even notice the lower light around. That’s wasting light. Mainly because the light is not distributed well within the beam.
For us it’s hard to give a buying advice here, because light is also something very subjective. What we can do, is encourage you to not only go for Lumen. Also focus on the beams. With the above in mind, compare your friends head lamps for example, keep bugging your outdoor dealer or follow our blog here. So that you find the right head lamp and the right beam for your activity and your terrain.
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