Halogen vs LED headlights: what to know before you swap a bulb

Verdict

Replace a halogen bulb with a halogen bulb of the same type, and consider a higher-output halogen if you want more light. Reserve LED for vehicles whose housings were designed for it from the factory, or for a complete housing assembly engineered and marked for LED.

Winter driving on I-580, US 395 and the Mount Rose Highway puts headlights to work for a good share of the day, and a burned-out bulb is one of the most common things our maintenance check catches. The question that follows is whether to put in another halogen or step up to an LED. The answer depends on the housing the car came with, and on a federal rule that most online bulb listings skip over.

Why the housing decides

A headlamp is a system: the light source, the reflector or projector lens, and the aim. A halogen housing is shaped around a filament of a specific size in a specific position, and the reflector gathers that light into a beam with a sharp cutoff that keeps it out of oncoming drivers' eyes. An LED bulb puts its chips in a different place and emits light in a different pattern. Even an LED that looks brighter from the driver's seat usually throws light above the cutoff and into the oncoming lane, and often less onto the road.

The federal standard for headlamps, FMVSS 108, requires the lamp to be designed and tested as a unit. NHTSA has stated that replaceable LED bulbs sold to replace halogen bulbs in halogen housings are not compliant, because the housing was certified with the halogen source. Nevada does not run a headlight-aim inspection, so the issue here is glare and real-world visibility rather than a test, but the rule stands.

Where LED belongs

Vehicles built in the last several years increasingly come with LED headlamps from the factory. Those housings were designed around the LED source, meet the standard, and give the long life and crisp beam LED is known for. They are also sealed units: when one fails, the whole assembly is replaced, which is a dealer or body shop job, not a bay job. If your car is one of these, the question on this page does not apply to you.

For an older car, the compliant LED path is a complete replacement headlamp assembly engineered for LED and marked as meeting the standard, not a bulb. That is a bigger purchase and installation than a bulb swap, and it is worth doing only on a vehicle you intend to keep.

Getting more from halogen

If the real complaint is not enough light, there are three things to check before buying anything. First, the lenses: a yellowed, hazed lens can cut light output badly, and a restoration kit or a new lens often does more than any bulb; see dim or yellowed headlights. Second, the aim, which drifts when a car is loaded or has been in a minor collision. Third, the bulb itself: higher-output halogens in the same part number are legal and noticeably brighter, at the cost of somewhat shorter life.

Replace bulbs in pairs when you can. Filaments age together, and a new bulb beside an old one gives a lopsided beam and a second visit within months.

What we do in the bay

The maintenance check looks at headlights, tail lights, brake lights and turn signals at every visit. If one is out, the technician looks up the part number for your year, make and model, shows you the bulb, and replaces it while you wait with a halogen of the correct type. We do not install drop-in LED bulbs in halogen housings. The bulb page lists what we replace, and the headlight bulbs guide explains the part numbers.