The lumen is one of the most common units for measuring the brightness of any given light source. Despite its ubiquity, it’s actually also one of the worst ways to gauge illumination. Here, we dispel some of the misconceptions behind luminance and shed light on, if you will, more accurate ways of determining headlight power. Regardless of whether you’re replacing a bulb to meet inspection or installing a light bar on your overland rig, the same rules apply.
What Are Lumens
To start, lumens simply measure the raw amount of light emitted from the individual bulbs that make up each headlamp. At one point in your life, you’ve likely heard the old saying that brighter lights throw light further. However, that isn’t exactly true.
Case in point: There are plenty of cheap light bars that you can buy on Amazon that promise ridiculous numbers like 50,000 lumens. As this number reflects just the light coming out of each headlamp, it’s a somewhat deceptive metric; manufacturers can simply pack in more bulbs and advertise an eye-popping lumen count. What this doesn’t take into account is the housing of the light itself, which can make a substantial difference.
According to KC HiLites—who make high-quality lights for overlanding vehicles—the size and geometry of the reflector, as well as the clarity of the lens, can greatly affect a headlight’s raw output. There are virtually hundreds of other factors that can affect how well that headlight actually helps you see what’s in front of you. For this fact alone, one set of headlights isn’t necessarily better than another just because the bulbs offer more lumens.
What Are Lux and Candela
Lux refers to the amount of usable light that lands on a certain surface—and is measured as how many lumens hit a single square meter of that surface. So a light that has a focused beam will put more lumens on the object, making it brighter, while a less focused beam will spread its lumens out and not show the object as brightly. This makes lux better for comparing how much illumination lights provide in the real world. Overlanding experts will know that manufacturers of off-road light bars also measure beam distance as well as pattern, which have quite a profound effect on the lux reading. When light is focused into a narrower beam, it theoretically becomes brighter. However, these would blind motorists and would leave your peripheral vision pitch dark.
Jon Tuico, a YouTuber and overland enthusiast, mentioned that his lights are actually measured by candela. Compared to lux, candela measures the total amount of light traveling in a certain beam angle and direction. It’s a great metric to evaluate the strength, volume, and intensity of any given light source.