# How to Choose The Brightest and Best LED Headlight Kit for Your Car? Read This Post with Detail Explanation.

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.