LED Headlamps offer bikers increased visibility and safety on the road. The after-market options are endless. Comparing different LED products can be confusing. This is something we discussed in “Make the ‘Bright’ Choice” and “Rats Nest 101”. How do you choose the best LED headlamp? We’ll walk you through a few factors to consider when choosing ‘the brightest headlamp’. But before jumping in, there are two key terms to know.
Lumen: Total “amount” of visible light present – this does not mean brightness! A lumen rating does not consider wasted light or electrical and real-world losses. These losses include thermal loss, optical loss and assembly loss.
Lux: A measure of the intensity of illumination on the target area from a distance. This is how much useful light gets delivered to the task/target area. Lux measures delivered light, discounting any waste.
Measuring Lumen Ratings
First, it’s important to understand how we measure lumen ratings. The lamp (LED headlamp in our case) gets placed inside an Integrating Sphere. The light from the lamp gets dispersed evenly over all angles in the sphere. With this equal distribution, we’re able to measure the total lumen produced. This is great for applications that need 360 degrees of illumination (i.e. a kitchen lamp). But, with a headlamp, you want the light in a targeted beam pattern. The total lumen rating doesn’t give any insight into how the product will perform in a real-life. So, with LED headlamps, the lumen rating is often misleading.
Also important to note: there are two different lumen measurements available. There are Raw Lumens and Effective Lumens. J.W. Speaker says, “LED lamp output values (Lumens) can vary dramatically depending on which values are being quoted”.
Raw V. Effective Lumens
Raw Lumens measure the theoretical output of a light. This gets calculated by multiplying the theoretical output of an LED by the number of LEDs in the lamp. For example, a lamp has 10 individual LEDs. Each LED gets rated with a maximum output of 100 lumens. That lamp will offer 1000 raw lumens.
Effective Lumens measure the actual output of a lamp. This takes into consideration inherent losses. Thermal loss occurs because less light gets produced as LEDs get hotter. Optical and assembly losses happen because of the lamp assembly. Light gets lost as it travels through the lens and/or can get lost within the lamp housing itself.
Lumen v. Lux
In turn, Lux provides a clearer picture of the products performance in an application. Again, lux measures the amount of delivered light to a task/target area (measured in square meters). The task area can be anything; a hallway, a desktop or, in our case, the road ahead. To measure lux, the light product is installed in it’s intended application. For a headlamp, this would mean installing the lamp inside the headlamp housing. Then, the amount of directed light delivered to the task area gets measured. Lux discounts any wasted light being that wasted light wouldn’t make it to the task area. For an LED Headlamp, lux factors the lumen output, the LED headlamp and the housing its installed into as well as the beam pattern produced.
Less Lumens but a Brighter Beam?
Some might argue then, that if an LED headlamp has a higher lumen rating that it would also be the brighter option. This isn’t the case. For example, Headlamp A emits 3,800 lumen and measures 360 lux at 25 feet. Headlamp B emits 3,700 lumen (100 less) and measures 1,360 lux at 25 feet. While Headlamp B provides 100 lumens less than Headlamp A, it delivers an extra 1,000 lux. Headlamp B will offer more light to the target area. Installed, Headlamp B will produce a higher quality, more concentrated beam pattern. While Headlamp A had the higher lumen rating, Headlamp B would perform better.
GTR Lighting (February 20, 2017) demonstrates this idea with automotive headlamps. The OEM Halogen Headlamp emits 900-1000 lumen, the GEN-2 LED emits 3,600 lumen and the GEN-3 LED emits 3,700 lumen. As you can see, while the GEN-2 LED offers triple the lumen than the OEM bulb does, it produces less lux. The GEN-2 beam pattern isn’t focused or concentrated to the target area. You can also see that while the GEN-3 LED only offers an extra 100 lumen than the GEN-2 LED, it offers an extra 1,000 lux! The GEN-3 LED produces a more concentrated beam pattern with superior performance. This is because of the improved design and engineering.
In fact, if the lumen rating remains constant, lux will be inversely proportional. Meaning, if we spread light out over a larger area, it illuminates dimmer. GTR Lighting exemplifies this in the findings, above. It doesn’t really matter that the lumen rating is higher. A poorly engineered lamp with an inferior design will have a decrease in lux. In turn, the lamp with have an unfocused, unusable beam pattern. Engineering and design ‘factors’ play a significant role. With LED headlamps and their performance, these factors are paramount. We elaborate on this point in our ‘Road Glide® Revolution’ blog.
Lumen Bias: the Eye-Sensitivity Curve
Another downfall of lumen ratings: it only considers the energy on visible wavelengths. Visible wavelengths relate to the human eye, which are all unique. There are varying sensitivities we must account for. For this, there is the ‘eye-sensitivity curve’. The curve applies different values to different wavelengths (colors) of light. The human eye is most sensitive to green light. The human eye is less sensitive to colors on the red or blue end of the spectrum. A green light will always appear brighter than a blue or red light – even with the same amount of energy powering it.
The Judd-Vos Correction
But, as time went on, it became clear that we were underestimating the blue end of the spectrum. The Judd-Vos correction shifted the curve. This change reflected the true sensitivity of the human eye to blue light. This is particularly important when considering LED light sources. Single-color LEDs radiate through a narrow band of wavelengths. This exaggerates the discrepancies of the eye-sensitivity curve. Incandescent light radiates throughout the visible band. So, the inconsistencies of the curve are less pronounced. Philips published a thorough technical brief on this point. Below, you can see how a lumen rating underestimates and distorts the perception of a blue LED source.
Color temperature can also affect the lumen measurement. Two lights emitting the same radiant energy can produce different lumens measurements. This is because of where they fall in the color spectrum.
Custom Dynamics® TruBEAM® v. ProBEAM®
The ProBEAM® LED Headlamp uses projector lenses and advanced optical D lenses. It offers 1250 Effective Lumens (high beam).
The TruBEAM® LED Headlamp uses both projector and reflector type LEDs. It offers 2947 Effective Lumens. This provides a wider beam pattern with light spread to either side.
The TruBEAM® Headlamps offer built-in LED Halo ring. This provides a more custom look that matches the aesthetic of our Dynamic Ringz™! The built-in halo does not contribute to the beam pattern/illumination. But, it does enhance the cosmetic appeal for many customers. The ProBEAM® headlamp offers a more modern, sleek look.
Both LED Headlamps are going to offer a far superior beam pattern than the stock headlamp. While they are brighter, they also offer a wider spread of light, making night time driving much safer. The ProBEAM® LED Headlamp offers a much more directed, centered beam pattern.