Rick's Free Auto Repair Advice

How to aim LED headlight bulbs

Can you aim LED headlight bulbs in a halogen headlight?

You’re not going to like what I’m about to tell you. If you’ve purchased LED headlight bulbs and installed them in headlights designed for halogen headlight bulbs, there is no way you can adjust the LED headlight bulbs to match the same beam pattern as the halogen bulb. It’s actually impossible to duplicate the proper beam pattern for many reasons:

LED Headlight bulbs don’t have the same size, shape and spherical dimensions as a halogen bulb.

By their very nature, LED bulbs have at least two flat bright spots, where halogen bulbs have a single 360° bright spot. Since the two circuit-on-board (COB) light sources in an LED headlight bulb are mounted on opposing sides, it is physically impossible for them to emit light in a 360° patters.  Yet, the headlight reflector (whether you have reflector style or projector style headlights) is specifically designed to match the size, shape and spherical dimension of a halogen bulb. So there is no way you can re-orient the LED COBs to match the halogen bulbs.

None of these LED bulbs match the size and shape of a halogen filament, so they can NEVER match the beam pattern.

LED headlight bulbs

The single filament in a halogen headlight bulb is rectangular with the brightest spot in the center of the filament. Look at the various number and shapes of LED chips on LED bulbs. Not only are they different shapes, but they’re located in different places so they don’t line up properly with the reflector’s focal point.

LED headlight bulbs will never match the beam pattern even in a projector headlight and you can aim an LED headlight bulb to work in a projector headlight

Many “experts” state that LED bulbs work just find in a projector headlight. They don’t. They can’t because you’re asking the projector headlight to defy the laws of physics.

How a projector headlight works

The reflector focuses the light to a “hot spot” located at a midway point between the reflector and the lens. The lens then projects this hot spot onto the road.

projector headlight with led bulb

Change the bulb and the beam no longer focuses midway between the reflector and the lens. So less light gets refocused on the road and since the focus is off, more light ends up as glare.

Why LED headlight retrofits don’t work in projector headlights

First, the LED light source isn’t a spherical 360°, so it can’t reflect to the midpoint properly. Second, since the reflector in a projector headlight (yes, they have reflectors) is designed for a halogen bulb, and LED bulbs don’t match the focal length, size and shape of a tungsten filament, the reflector it can’t place the hot spot in the pre-determined midway point between the reflector and the lens. The lens will project less light on the road and produce more glare into oncoming traffic simply because the light is in the wrong place inside the headlight.

Retrofitting LED headlight bulbs into a halogen headlight is illegal

Yes, you read that correctly. Carmakers self-certify their headlights to meet the specifications in Federal Motor Vehicle Safety Standard (FMVSS) No. 108, Lamps, Reflective Devices and Associated Equipment. So the headlight and bulb are designed and certified together. You cannot change the bulb type and still meet the specifications.

In other words, if you change from a halogen bulb to an LED headlight bulb, your headlights can no longer meet the requirements set forth in Federal Motor Vehicle Safety Standard (FMVSS) No. 108, Lamps, Reflective Devices and Associated Equipment.

©, 2021 Rick Muscoplat

Posted on by Rick Muscoplat



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