Can you retrofit LED bulbs into a halogen headlight?

Here’s why you should never retrofit LED bulbs into a halogen headlight?

First, it’s illegal everywhere in the U.S., Canada, and most other Countries to retrofit LED bulbs in a halogen headlight assembly. Here’s why.

In the U.S. carmakers self-certify their headlights to meet the specifications listed in the 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 fact, it’s optically impossible for a retrofit LED bulb to work properly when installed into a headlight designed for a halogen bulb. That’s why there isn’t s a single LED bulb being sold that’s approved for street use; because the manufacturer can’t legally claim their street legal

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.

The same is true in all other countries that require carmakers to meet lighting specifications.

There isn’t a single LED retrofit bulb sold anywhere that’s street-legal to replace a halogen bulb

There isn’t a single LED or HID retrofit that contains a D.O.T. marking. Most retrofit bulbs say they’re “for off-road use only,” or they don’t say anything on the package.

2) Why retrofit LED can’t produce the proper beam pattern

The LED light source is totally different from a filament bulb and that prevents the headlight from producing the proper beam pattern

• Halogen bulbs have a single filament light source that’s cylindrical and casts light in a 360° pattern. The reflector and lenses in reflector and projector headlight are designed to properly reflect and focus the light from this light source

• LED bulbs have two flat light sources that only cast light in 270°, so when they’re used in a reflector or project headlight there will be 90° of dead spots.

Because halogen headlights aren’t designed for two flat light sources, they can’t produce the proper beam pattern. Here’s what happens when you install LED bulbs in a halogen headlight assembly:

• Because the reflector and lens are designed for halogen bulbs, they produce GLARE and BLINDING when fitted with LED bulbs

• LED bulbs in a halogen headlight produce more light scatter and actually throw less light on the road and produce the wrong beam pattern.

Many “experts” state that LED bulbs work just fine in a projector headlight. They don’t. They can’t because you’re asking the projector headlight to defy the laws of physics. Scroll down to learn why it’s optically impossible for an LED retrofit to produce the proper beam pattern when installed in halogen projector headlight assembly

3) LED retrofit bulbs produce the wrong light color

The blue light from LED retrofit bulbs produces more glare

• Traditional halogen bulbs produce light at around 3,000° Kelvin; towards the red end of the spectrum. But LED bulbs produce light in the 5,000 to 6,000° K spectrum.

Blue light travels at shorter wavelengths (450 to 495 nanometers) and higher frequencies, causing air particles to oscillate faster and scatter in the atmosphere more than other colors. This applies to ALL blue light sources, whether LED or HID.

That’s why the headlight assembly must be designed specifically for the bulb type. Putting an LED bulb into a halogen headlight assembly produces more glare and the blue color reduces driver visibility.

Retrofit LED headlight bulbs will never match the beam pattern even in a projector headlight and you can’t aim an LED headlight bulb to work in a projector headlight

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.

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.

©, 2021 Rick Muscoplat