Rick's Free Auto Repair Advice

Convert to LED headlights?

Can you convert halogen headlights to LED headlights?

If you’re asking if you can throw an LED headlight bulb into a headlight assembly designed for halogen bulbs, the answer is a resounding NO!. It’s not legal. It’s not safe. And, it’s not going to get you better night vision.

Why isn’t it legal to convert a halogen headlight assembly to LED?

First, when a carmaker designs a headlight assembly, they follow beam patterns and brightness specification regulations from The National Highway Safety Transportation Administration (NHTSA), an agency of the U.S. Department of Transportation (DOT). All Headlamps and Taillamps must comply with the Federal Motor Vehicles Safety Standard (FMVSS 108) and Part 564.

The carmaker must certify that their headlights meet the DOT regulations. To meet those regulations, carmakers design the reflector and lens combinations designed for a particular bulb. If you substitute a different bulb into that same housing, even if the bulb fits properly, it will not produce the same results and the headlight will no longer meet DOT regulations. You cannot tilt or swing the headlight around to “refocus” the new beam pattern to compensate for the LED bulb because moving the headlight assembly moves all the light patterns, not just the ones that hit the road in the right place. So while you’re realigning to throw more light on the road, you’re also throwing more glare into oncoming traffic.

What’s different about LED bulbs compared to halogen bulbs?

First, to get the same light output, LED bulbs have at least two, if not more LED chips. In other words, they have multiple light sources, where a halogen bulb only has a single light source; the tungsten filament.

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.

Right off the bat, the multiple light sources of LED bulbs and their differing distances from the rear of the reflector changes the way the light bounces off the reflector, producing scatter which result in glare. Again, the reflector is designed for a particular bulb’s distance from the reflector, the shape and size of the light source and the brightness of the light source. Change any one of those factors and the headlight assembly won’t focus the beam in the same way.

LED bulbs seem bright, but they put less light where you need it

Since the reflector wasn’t made for multiple light sources at differing distances from the focal point, the reflector can’t produce the same beam pattern on the road. So even though the LED bulb will look brighter, it will cast LESS light on the road than the bulb the headlight was designed for.

dual filament headlight bulb

Here’s a typical high and low beam setup with a traditional reflector headlight assembly. The focal point of the filament is critical to casting the most light on the road or down the road. Change the focal distance and you change where the light goes. LED bulbs don’t have the bright spot in the same place as halogen bulbs.

Projector headlight

Projector headlights focus the light at a spot between the reflector and the lens. The lens refocuses the light on the road. Change the bulb and you change the location of the mid-way bright spot, resulting in less light on the road.

LED bulbs don’t work in a halogen projector assembly either

A projector headlight assembly works a bit differently than a typical reflector headlight. Most use a parabolic reflector that focuses the light at a spot between the reflector and the lens. The lens then refocuses that bright spot and projects the light onto the road. If you change the shape of the light source, the distance from the reflector or the number of light sources, you change where the bright spot falls between the reflector and the lens, preventing the lens from projecting the entire amount of light onto the road.

©, 2020 Rick Muscoplat

Posted on by Rick Muscoplat


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