LED Headlight Design & Misconceptions

Recently an article came out in Consumer Reports about LED headlights on cars, and as a lighting engineer it was frustrating to read due to the misconceptions and myths that are perpetuated by it. So thought I would take some time to point out the issues. Even though this doesn’t really have anything to do with traditional bike lights, the concepts are the same!

https://www.consumerreports.org/headlights/led-headlights-can-be-brighter-but-often-lack-clear-advantages/

 

The headline for the post is “LED Headlights Can Be Brighter but Often Lack Clear Advantages.

The main argument being made in the article is that the light source themselves are the key to whether a headlight is bright enough, which couldn’t be further from the truth. There is a lot that goes into a successful headlight, and CR’s testing methods are also quite questionable.

 

LED Headlight Design Requirements

Let’s first go over what a lighting engineer has to work with when starting a new design from scratch. This applies both to vehicle headlights, and bike lights. There are several criteria that is often evaluated.

  • How many lumens to work with.
    • This is defined mostly by how quickly and effectively heat can be wicked away from the LED source. In automotive headlights there are large heatsinks that are often passive, although some headlights use internal fans to have air rushing over there to pull heat away.
    • In bike lights, this is often defined by the size of the headlight in a well engineered light. It is easy to put 2000 lumens in a tiny matchbox size light, but the second it’s turned on and being used for more than 30 seconds it will overheat, and pull power to save itself. Rendering it more like a 500-600 lumen light.
  • Beam pattern requirement
    • This is often defined internally by the OE manufacturer. They will have a set of requirements for lighting targets to hit at certain points in the beam pattern. Some manufactures value beam width over center intensity, others focus more on downrange intensity. Lots of simulation and testing goes into defining these targets.
    • For bike lights, we do something similar where we ride our favorite trails, and make note of where and how much light we would like to see in a system.
  • Cost targets
    • Pretty obvious one, but it constrains the lumen requirements. The LED chips themselves are not cheap, and in order to get higher lumen numbers need more supporting systems such as fans or larger heat sinks.
  • Styling
    • There are a few methods of LED lighting for automotive that are used to create the beam pattern, but usually different styling requirements drive this.

 

The main portion of a lighting engineers development comes from the beam pattern. With software such as Lucidshape we can shape the light to create specific beam patterns. With LED’s it is actually easier to control the lighting then with Halogen or HID bulbs because the actual emitting source is smaller.

 

LED’s can’t shine down the road?

The myth of “LED’s can’t shine further down the road” is the one that is the most frustrating. The ONLY thing that matters about the source of light, is the lumens and the color. It is the reflector design that determines how far you see down the road or how wide the beam pattern is.

The Trail Edition and the Road Edition are good examples of this.

 

Both use the exact same LED chip, the exact same driver setup, and the exact same castings. The only thing different is the reflector. The Trail Edition is optimized for beam with and even illumination, while the Road Edition offers nearly twice the “punch” at the expense of less width. Each one designed for each specific task.

Automotive headlights are similar. OE Manufacturers optimize their headlight for the majority of customers. European and Japanese headlights tend to focus more on low beam width and even illumination since European and Japanese drivers find themselves in city centers more often. They also tend to use the high beam far more often. Interestingly enough North American drivers do not use the high beams very often, even in situations where they should be. For that reason a lot of domestic OE’s have low beams that have more center punch, and seem “brighter” in these tests that Consumer Reports does.

 

 

1 Comment to “ LED Headlight Design & Misconceptions”

  1. Ed Smith says :Reply

    Thank you!
    Are there any specific design features that someone should look for or avoid when selecting automotive aftermarket LED headlight bulb replacements?

    Obviously it needs to be a physically and electrically compatible bulb; there is a wide selection available at this point that fit this for most vehicles.
    What about the physical location of the LED chip emitters? Some automotive LED headlight makers make a big deal about precise positioning of the emitter chips to match the location of a halogen filament. This seems like it should be important.

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