When looking for new headlights, such as LED headlight bulbs, everyone really wants to figure out “What’s the brightest headlight bulb?” Well to answer that question also to truly get yourself a better picture of what “brightness” is, we need to get scientific and define a few terms. But not to be concerned! I will make this content as easy as possible to wrap your mind around. So stick to me for a while and you’ll be able to check true headlight the best 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 full total amount of visible light emitted by a source.

Lux: A unit of measurement for illuminance which is a measure of just how much luminous flux is reflected on a particular area.

“One can regard luminous flux (measured in lumens) as a way of measuring the total “quantity” of a visible Light present, and the illuminance (measured in lux) as a way of measuring the intensity of illumination on a surface area at a specific distance from the source.”

So let’s consider these definitions as we see how lumen and Iux amounts are measured and how that procedure applies to headlight bulbs.

Luminous flux, which I’ll just make reference to a lumen, is measured within a device named the integrating sphere. A bulb is positioned in the sphere and the light given off by the bulb is scattered by the inside of the integrating sphere and evenly distributed 360 all angles. The total lumen amount of a source of light could be measured accurately since light could be captured from all angles in the sphere. While this technique of measuring the brightness of a bulb is effective for light applications where 360 degrees of light is needed, (like a desk lamp) the lumen amount is half of the story while testing the brightness of headlight bulbs. For this reason, illuminance and lux are so important.

Lux is measured by installing the bulb in the headlight housing and testing to see how well the lumen quantities are projected or reflected out of the housing. In this situation, we measured the beam pattern reflected from the headlight housing and bulb combination on a wall 25 feet away. From this distance and this position, we’re able to start to see the lumen amounts from the bulb that are really being utilized and converted into a usable beam pattern by the headlight housing. When measuring lux in this way, we’re able to check 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 factors when calculating lux in this manner.

(A digital light meter used to measure lux. In this application, lux is being measured in a beam pattern created by a LED bulb inside a headlight housing.)

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 lighting brightness.

“A given amount of light will illuminate a surface more dimly if it is spread over a larger area, so illuminance (Iux) is inversely proportionaI 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 in the 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 will be “bright” on paper, but not actually usable inside a real-world scenario. Below we see an example similar to this situation within a 2014 Honda CRV 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 one halogen bulbs typically emit 450-500 lumen, and this one stock bulb was measured at 210 lux at 15 feet(no enough distance on the garage to test at 25 feet distance) with this headlight housing.

And one pcs of F1 LED headlight bulb emits 2500 lumen and was measured at 600 lux at 15 feet inside this Honda CRV headlight housing. That LED bulb in that headlight housing really produced less lux than the share bulb even though it has 4-times the lumen. The difference can be seen when comparing the two beam patterns. The additional lumen amounts are not concentrated as precisely within this CRV headlight housing as the stock bulbs are. The result is a beam pattern much less concentrated and arguably less brilliant.

Now compare both LED bulbs. one pcs of F1 LED headlight bulb emits 2500 lumen and was measured at 600 lux at 15 feet inside this Honda CRV headlight housing. Whereas the C7X LED headlight bulb emits 2000 lumen per bulb (less 500 lumen) and had been measured at 1,210 lux at 15 foot inside this headIight housing.

This buIb is emitting less lumen lighting amount but higher lux amounts inside this headlight housing. Take a look at the beam designs and you’ll see why. This Directed bulb is capable of producing a beam pattern that is more focused versus the other Brought bulb, and more closely matches the share bulb beam pattern. And this boost of just one 610lux will be achieved by no lumen increasing but decrease 500 lumen per led bulb in light output. This is achieved through a better-designed buIb that interacts with the headlight housing much like a stock halogen bulb would.

All that to say, when you compare the brightness of headlight lights, make sure to look at the big picture. With LED headlight bulbs especially, make sure you take into account the beam pattern the Directed bulb creates when placed inside a headlight housing. Look at more than just the advertised Iumen amounts-if the manufacturer gives lux figures 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.