When looking for new headlights, such as LED headlight bulbs, everyone wants to know “What’s the brightest headlight bulb?” Well to answer that question and to truly get a better picture of what “brightness” is, we need to get scientific and define a few terms. But not to worry! I’m going to make this article as simple as possible to wrap your head around. So stick with me for a moment and you’ll be a pro when it comes to figuring out and understand true headlight brightness.
The two main words to define as we talk about headlight brightness are lumen and lux.
Lumen: A unit of measurement for luminous flux which is a measure of the total quantity of visible light emitted by a source.
Lux: A unit of measurement for illuminance which is a measure of how much luminous flux is spread out over a given area.
“One can think of luminous flux (measured in lumens) as a measure of the total “amount” of visible light present, and the illuminance (measured in lux) as a measure of the intensity of illumination on a surface at a particular distance from the source.”
So let’s think about these definitions as we see how lumen and lux amounts are measured and how that process applies to headlight bulbs.
Luminous flux, which I’ll just refer to as lumen, is measured inside of a device called an integrating sphere. A bulb is placed inside the sphere and the light given off by the bulb is scattered by the interior of the integrating sphere and evenly distributed over all angles. The total lumen amount of a light source can be measured accurately since light can be captured from all angles from inside the sphere. While this method of measuring the brightness of a bulb works well for lighting applications where 360 degrees of light is needed, (such as a table lamp) the lumen amount is only half of the story while testing the brightness of headlight bulbs. This is why illuminance and lux are so important.
Lux is measured by installing the bulb inside a headlight housing and testing to see how well the lumen amounts are projected or reflected out from the housing. In this instance, we measured the beam pattern created from the headlight housing and bulb combination on a wall 25 feet away. From this distance and this position, we are able to 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 are able to take into account 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 headlight housing, the resulting beam pattern, and distance are all factors when calculating lux this way.
So you’re probably thinking, “Well then, doesn’t that mean a headlight bulb with the highest lumen amount will be the brightest?” Maybe. Remember, lumen amounts are only one piece of the puzzle when determining usable light brightness.
“A given amount of light will illuminate a surface more dimly if it is spread over a larger area, so illuminance (lux) is inversely proportional to an area when the luminous flux (lumens) is held constant.”
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 spread out or unfocused. A headlight like this would be “bright” on paper, but not actually usable in a real-world scenario. Below we see an example similar to this scenario in a 2007-2013 Toyota Tundra headlight housing. Two LED bulbs were tested here along with the stock bulb, but take a look at the beam patterns and lux numbers.
Original equipment halogen bulbs typically emit 900-1,000 lumen, and this stock bulb was measured at 530 lux at 25 feet with this headlight housing. The GTR Lighting GEN 2 LED bulb emits 3,600 lumen and was measured at 360 lux at 25 feet inside this headlight housing. That LED bulb in that headlight housing actually produced less lux than the stock bulb even though it has 3-times the lumen. The difference can be seen when comparing the two beam patterns. The additional lumen amounts are not focused as precisely within this Tundra headlight housing as the stock bulbs are. The result is a beam pattern less concentrated and arguably less bright.
And this increase of 1,000 lux is achieved by only a 100 lumen increase in light…
Now compare the two LED bulbs. The GTR Lighting GEN 2 bulb emits 3,600 lumen and was measured at 360 lux at 25 feet inside this headlight housing. Whereas the GTR Lighting GEN 3 bulb emits 3,700 lumen (only 100 more) and was measured at 1,360 lux at 25 feet inside this headlight housing. This bulb is emitting high lumen amounts and high lux amounts inside this headlight housing. Take a look at the beam patterns and you’ll see why. This LED bulb is capable of producing a beam pattern that is more concentrated versus the other LED bulb, and more closely matches the stock bulb beam pattern. And this increase of 1,000 lux is achieved by only a 100 lumen increase in light output. This is achieved through a better-designed bulb that interacts with the headlight housing much like a stock halogen bulb would.
All that to say, when comparing the brightness of headlight bulbs, make sure to look at the big picture. With LED headlight bulbs especially, make sure you take into account the beam pattern the LED bulb creates when placed inside a headlight housing. Look at more than just the advertised lumen amounts–if the manufacturer gives lux numbers look for those too. Also, see how the bulb itself is designed and look for bulbs that more closely fit the profile and dimensions of a stock halogen bulb.
Clear as mud
So which way is best measure, lux or luman?
Lux is the actual usable light output, so that would make more sense. Lumen will change depending on the housing.
Not much point in writing an article that you need a doctors degree in lighting to understand, sounds like the author is more trying to impress us with his knowledge than explain anything. Goes right back to the statement, if you really understand something, you can explain it simply in plain english.
The author explained it in plain english right above your comment, and the timestamp was before your own comment. Does that statement about understanding things include reading comprehension?
I am still confused. Can’t Lux Vs Lumens be broken down to “spot vs flood” So which one throws the light further?
Lux is the illuminance measurement of the target surface. Lumen is the raw volume of total lighting power.
Let’s put into a somewhat more familiar concept. Imagine garden hose with selectable nozzle. Like,, Soak, Mist, stream.
In this case, the lumen is volume of the water coming out from the faucet.
When you select “Mist”, it spray wide angle but it does not reach much distance. If you stand at, let’s say 1m from the hose nozzle, water spraying on you, you will feel water hitting you very gently.
This degree of pressure you feel is Lux.
When you select “Stream”, with the same amount of water supply, it reaches more distance, and at the same 1m of distance from the hose nozzle, you will feel more pressure where it hitting you.
This explains, higher the lux number, reaches farther.
Then, what if you stand at 2m of distance, “mist may not even reach to you, “stream reach to you, but you will feel less pressure. This is because more distance from the hose nozzle. So lux number changes depend on measuring distance. Telling Lux reading without specifying the distance is meaningless.
then, what measurement makes most sense?
In lighting measurement, what it should be used is Candela. Candela is, how intense water is projected from the hose nozzle. Since this number indicates projection source, it does not matter the measuring distance. Always same. It is calculated by Lux and measurement distance.
Lux is end result number at specified distance, how strong light reached to target surface. Candlea is the calculated intensity of how strong light was projected from the light source.
In this example, nozzle selection is like optic selection. Stream is a high focus Spotlight, Mist is a wide flood beam.
Even with massive amount of water supply ( raw lumen), if it selected ” mist” nuzzle, it just does not reach far, because there is no intensity to project.
On the other hand, if Stream selected, even with smaller amount of water supply, it reaches far.
In summary, higher lumen is “Potential”. Higher lux is a more intense end result of the “selected” measurement point. It can be translated as how well optically focused.
Of course, this is based on all water enters the hose nozzle from the same diameter of the faucet exit.
If water supply does not go in to nuzzle, ( out of focus) then, it leak at the base, scatter, and not much of end result you can expect. That’s where how accurately, filament position, size, and character is designed.
I hope this helps you understand better!