Before You Buy: Off-Road Lights Lumens vs. Lux, and Why Lux is More Important

Shopping for off-road lights turns into a giant pain in the ass in one hell of a hurry with every company and online retailer throwing stats at you about whatever lighting system they’re trying to hock (us included. We’re sorry). The most common term you’ll see when shopping around is "Lumens" and the lumen wars have reached a point of utter ridiculousness. eBay is rife with LED light bars that advertise an ever-expanding lumen output with some bars supposedly throwing out 500,000 lumens or more. As impressive as some of those numbers are, the sad truth of it all is that if even those bars are coming close to that lumen output in the real world (they’re not), it wouldn’t really matter all that much. In the end, lumens is a pretty poor indicator of how effective a light bar operates. A much better determinant of the actual, real-world effectiveness of a given off-road LED light is lux. Specifically lux at a fixed range.

Lumens vs. Lux
Before we get into the "whys", we do need to understand the "whats" and what they actually mean. Both lumens and lux are both measurements of light, but they do it in two different ways that may not seem all that different at first glance, but make a huge difference when you’re judging the real-world capabilities of a given light or light bar.

Lumens are an SI unit that measures the luminous flux of a light source, which is the quantity of light emitted per a single unit of time.

Lux is as an SI unit of measure of lumens over a surface area. In fact, one lux equals one lumen per square meter

"Okay," you say, "but aren’t those two things more or less the same thing? Why add the work of figuring out lux if it’s just lumens anyway?" Well, little Timmy, we’re getting into that right meow.

The Problem with Lumens
Lumens seems like the most straightforward and simple way to measure the power of a light or light bar, but it has a few significant problems due to the ways it’s measured that manufacturers are more than happy to take advantage of.

First and foremost, lumens is almost always measured at the light source itself. In the case of off-road LED lights and light bars, that means measurements are taken right at the diodes emitting the light. This poses a problem since measuring at the diode essentially ignores the rest of the light, especially the part of the light that’s arguably just as important as the light source itself: the optics. The optics of the light are what dictate how the light emitted by the diode is getting harnessed, what beam pattern is being produced, and how effective that beam pattern is actually going to be.

A given light can have some ridiculous lumen rating, but if they’re using optics made from shards of public bathroom mirror hot-glued inside the light housing, it’s not going to generate a beam that’s anywhere near as effective as a light or light bar that has a lower lumen output, but has optics that are actually designed and constructed well.

Granted, you can chuck enough lumens at bad optics to overcome their inherent crappiness. But by the time you get to that point, you end up with a light with such high power needs that you burn amperage from your vehicle’s electrical system that’s probably better spent elsewhere.

Why Lux is Better
Unlike lumens, lux is measured at a distance away from the light or light bar (usually 10 meters). Measuring away from the light takes into account both the LEDs themselves and the optics, which gives you a much better idea of how well a light is going to perform out there in the real world. You’ll probably notice in your travels around the interwebs that the vast majority of Chinese light bars don’t have lux stats at all, and it’s to avoid looking awful in comparison to higher-quality light bars. While lux can be cheesed a bit, it can’t be outright abused like lumen values can and often are.

Lux values should still be taken with a grain of salt (unlike the truckload you need to swallow down with lumens). While they’re still a better gauge of a light, lux measurements are still taken in a very controlled environment with brand-new, off-the-assembly-line units that are going to provide a much better lux measurement than something being used out in the field in different ambient conditions, with dirty lenses, after general wear and tear, etc.

You’ll also need to be careful when comparing lights and light bars and only look at the lux values of lights that have have similar beam patterns. A flood or diffused beam light is going to have much lower lux than a spot, driving, or combo beam and you’ll want to avoid an apples to oranges comparison.

So, when you’re shopping around for off-road lighting for your rig, let lux be your guide and don’t get too excited about the latest $50 light bar rocking its elventy-seven berjillion lumens with a conspicuous lack of a lux measurement. It probably sucks in all sorts of fun ways that you won’t find out about until you’re in the dark someplace off-road.