The Difference Between Lux and Lumens: A Guide to Headlight Brightness

When most vehicle owners are looking for brighter lights for their vehicles, the thing that everyone considers the most is the lumens of the LED bulbs.

Because the higher the lumens of the bulb, the brighter it is and the better view you get, but is this correct?

Well to answer that question and truly get a better picture of what “brightness” is, we need to get scientific and define some terms. In this article, we'll dispel some of the misconceptions behind brightness and show you how to determine brightness more accurately.

When we talk about headlight brightness, the two main words to define are lux and lumens.

What Is The Difference Between Lux And Lumens？

LUMEN

The lumen (symbol: lm) is the unit for luminous flux. It indicates the total amount of light emitted by the light source, no matter where the direction is. It is important to mention that efficiency is especially important in lumens, as it indicates how efficiently the light source converts power into light. It is called the Lumen / Watts ratio (Lm / W). And this is why most people recommend upgrading dim halogen lights to LED lights because LEDs are more efficient at converting lumens with the same wattage output.

LUX

The lux (symbol lx) is a unit of illumination used to measure the amount of light output in a given area - one lux is equal to one lumen per square meter.

The brightness of the light source, the direction, and the distance of illumination all have an impact on the Lux.

If lumens are the raw amount of light emitted by the headlight itself, then lux is the amount of light available on the road

Why Do Most Vendors Label Lumens Instead Of Lux?

The first thing we need to do is to understand how the manufacturers of LEDs determine the lumens of LED lights.

We measure the lumen of a LED bulb kit within a device called an integrating sphere. A bulb is positioned in the sphere and the light given off by the bulb is scattered inside the integrating sphere and evenly distributed to 360 degrDees. Since the light can be captured from all angles in the sphere without any interference from other light sources, the total brightness of the light source can be accurately measured. This makes all the parameters of the light labeled with a certain reference.

Many manufacturers can not accurately define the luminous parameters of LED lights by Lux - measuring lux along a specific output is somewhat difficult, you must consider the distance of the light source.

It is also important to understand that lux is not the best measure for automotive use because automotive housings are designed for use with incandescent bulbs, which evenly distribute light in all directions. Your different housings are designed for different purposes- for example, a headlight will collect and focus the light forwards, and a side marker will collect and disperse the light to as much area as possible. Because the housing can modify the light path of the bulb, the same bulb can look completely different in two different housings.

That's why most manufacturers choose to label their LED bulbs with exact lumen values on the packaging to give customers the best idea of total light output.

When You Choose A Headlight Bulb, Lumen Or Lux Is Better?

For headlights, Lux is a much more accurate—though rarely talked about—metric for how well they’ll illuminate the road.

The reason is that state laws do not use "brightness" as the measure ways, but rather distance. For example, some states’ laws say that your lights must illuminate up to 115 feet from your car. As long as your light reaches that distance, then it is legal.

Headlights are more akin to directional lighting than lights in other locations, focusing on the illumination reaching the targeted area rather than on the brightness of the light source.

The size and geometry of the headlight's reflector, as well as the clarity of the lens, can greatly affect a headlight's raw output. Not only that, but if you want to upgrade your original halogen lamps to LED bulbs, the design of the LED bulbs, such as the wick location and size, will indirectly affect the light output.

It is possible for a bulb with high lumen amounts to focus poorly once placed inside a headlight housing due to poor engineering and design. The result would be an unfocused beam pattern with light reflected or projected poorly. In that case, a poorly focused beam pattern from a bulb with an initially high lumen amount would have low lux measurements because the light is scattered or unfocused.

Therefore, a bulb with more lumen does not mean more light is available on the road. If you want usable light to ensure you drive safely at night, you need to focus on the lux of your headlights. I'll describe how to measure lux and summarize next.

How To Test Headlight Brightness?

One of our fans Jason has reviewed several of our series of headlight bulbs in detail, and here is his test procedure with data from multiple tests conducted.

Lux is measured by installing the bulb inside a housing and testing to see how well the lumen amounts are projected or reflected out from the housing. In this instance, Jason measured the beam pattern created from the housing and bulb combination on a wall 20 feet away. From this distance and this position, we can see the lumen amounts from the bulb that are truly being utilized and turned into a usable beam pattern by the headlight housing. When measuring lux this way, we can consider multiple factors playing into the brightness of the bulb and find a clearer picture of true, usable light. The lumen amount from the bulb, the relationship between bulb and housing, the resulting beam pattern, and distance are all factors when calculating lux this way.

Whether you want to test the brightness of your headlights or find some reference recommendations before you plan to buy, this makes sense.

*Jason's tests aren't for lux number accuracy but for comparison to stock.

List of items:

①2017 Toyota Camry H11 Headlight Low Beam(For projector testing)

②2018 Ford F150 H11 Headlight Low Beam(For reflector testing)

③A spectrometer or small handheld light meter

*If you are testing on a vehicle, please note the aiming of the headlights, which can be found in our previously published Blog-"HOW TO PROPERLY AIM AND ALIGN THE HEADLIGHT?"

Test Results

To facilitate data viewing and comparison, provide test results first, followed by test details.

Halogen Lamp Testing

AUXITO H11 LED Bulbs Testing

10S Series H11 LED Bulb

• 52W/set, 6000LM/pcs, 6000K

The lux projected on a wall at a distance of 20 feet in a projector is 1.6 times the lux of the original halogen lamp; the lux projected on a wall at a distance of 20 feet in a reflector is 1.7 times the lux of the original halogen lamp. So the Q16 series front lighting bulb will increase the available lighting by 1.6-1.7 times.

M3 Series H11 LED Bulb

• 60W/set, 6000LM/pcs, 6500K

The lux projected on a wall at a distance of 20 feet in a projector is 1.9 times the lux of the original halogen lamp; the lux projected on a wall at a distance of 20 feet in a reflector is 2.2 times the lux of the original halogen lamp. So the Q16 series front lighting bulb will increase the available lighting by 1.9-2.2 times.

Q16 Series H11 LED Bulb

• 100W/set, 10000LM/pcs, 6000K

The lux projected on a wall at a distance of 20 feet in a projector is 2.5 times the lux of the original halogen lamp; the lux projected on a wall at a distance of 20 feet in a reflector is 3.5 times the lux of the original halogen lamp. So the Q16 series front lighting bulb will increase the available lighting by 2.5-3.5 times.

Y13 Series H11 LED Bulb

• 80W/set, 8000LM/pcs, 6500K

The lux projected on a wall at a distance of 20 feet in a projector is 1.5 times the lux of the original halogen lamp; the lux projected on a wall at a distance of 20 feet in a reflector is 2.3 times the lux of the original halogen lamp. So the Q16 series front lighting bulb will increase the available lighting by 1.5-2.3 times.

Closing Thought

When you choose a led headlight bulb, the most matter is the light on the road. Not the raw lumens of the lamp, but the functional lux appearing on the surface. A high-lumen output LED headlight kit doesn’t necessarily mean you will receive a functional amount of light on the surface. Based on our testing above, the available light output of the light is affected by the type of headlight assembly and the light pattern obtained is also assembly-dependent.

The following is a summary based on this test.

1. The brightest light (highest Lux)

The Q16 series LED bulb provides 3 times more usable light than the original halogen.

2. Higher output efficiency

The M3 Series LED bulb provides more than 2 times the brightness with 30W/pcs

3. Optimal beam pattern

The Y13 series LED bulb 360-degree lighting with the best cut-off pattern.

When choosing a product, please pay attention to the individual product parameters on the detail page so that you can choose the best front lighting for your car.