The complete guide
HB4 9006 LED Headlight Bulbs - A Practical Buyer's Guide
The problem this set is meant to solve
Open the bonnet on most older vehicles and you will find a halogen bulb that has slowly faded over the years. Halogen output drops as the filament ages and the glass clouds, and because it happens so gradually, nobody notices until the day a new bulb goes in beside the old one. Then the difference jumps out.
The other complaint is colour. Halogen light is yellow. That is not a fault, it is simply what a hot filament produces. For a lot of people, especially anyone building a show car or tidying up an off-road rig, that yellow look is the thing they want gone.
A pair of HB4 9006 LED headlight bulbs answers both of those at once. You get a clean 6000K white instead of yellow, and you get two fresh bulbs rather than one new one fighting an old one. Before you go further though, read the next section properly, because it decides whether this product is right for you at all.
Where these bulbs can and cannot be used
These are LED conversion bulbs. They go into a housing that was designed and built around a halogen bulb. In Ireland, that swap is generally not permitted on public roads, and we are not going to dress that up.
So this set is sold for off-road, show and private property use. Think competition vehicles, trail machines, static displays, workshop builds and anything that lives off the public road network. If you need bulbs for a car you drive to work, this is not the product for you, and we would rather tell you now than after the parcel arrives.
That restriction has nothing to do with the quality of the bulbs. It is about the type of product and the housing it goes into. Keep it in mind as you read the rest of the guide.
How an LED conversion bulb actually works
A halogen bulb is simple. Current heats a filament, the filament glows, and you get light and a great deal of waste heat radiating out in every direction. The housing behind it was built with that in mind.
An LED bulb works differently. Small chips sit on a metal base and produce light when current passes through them. They throw far less heat forwards, but they do create heat at the chip itself, and that heat has to go somewhere or the chip suffers. This is the single biggest design problem in LED bulb design, and it is why every decent bulb has some form of cooling attached.
There are two usual answers. One is a passive braid, a flexible rope of metal strands that hangs off the back and sheds heat into the air. The other is an active fan. This bulb uses a fan, and the fan is built into the body rather than bolted on behind it. That matters for packaging, because a fan inside the body keeps the overall shape more predictable than a braid that needs room to splay out.
Reading the specification
Six facts are confirmed for this product, and it is worth understanding what each one actually tells you.
The fitting is HB4, also listed as 9006. Same base, two names. If your old bulb carries either stamp, the base matches.
The colour is 6000K. Kelvin is a colour scale, not a brightness scale. Lower numbers look warm and yellow, higher numbers look cool and blue. At 6000K you are in clean white territory with a slight cool lean, which is the look most people are after when they search for the best 6000k led bulb.
The pack holds two bulbs. The light source is LED. The ingress rating is IP60, and that pair of digits deserves a sentence of its own. The 6 is the dust figure and means dust tight. The 0 is the water figure and means no rated water protection. So these are bulbs that belong inside a sealed headlight housing with the dust cap properly refitted, not bulbs you can hose down.
Checking fitment before you order
Fitment here is by fitting type only. We can tell you the base is HB4 and 9006. We cannot tell you it fits a named vehicle, and nobody should be telling you that without having tried it on that exact car.
Two checks do most of the work. First, read the code on your current bulb. It is usually moulded into the plastic base. Second, look at the space behind the headlight housing with a torch. LED bulbs are longer and wider at the base than the halogen they replace, so you need to know whether the body will clear the bulkhead, the air box, the battery or whatever else is crowding that corner. Also check the dust cap, because some are shallow and will not refit over a longer bulb.
If space is tight, there are deeper dust caps and extended caps available separately. Working that out before you order saves a return.
The electrical side, and why some cars complain
Modern vehicles often monitor their lighting circuits. The system checks how much current each bulb draws and compares it to what a halogen bulb should pull. An LED bulb draws less, so some vehicles read that as a blown bulb.
The symptoms vary. You might get a warning on the dash. You might get a flicker, or a strobe when the lights first come on, or a bulb that will not settle. None of it means the bulb is faulty, it just means the car's checking circuit is not happy.
The usual answer is a CANbus decoder, a small in-line module that sits between the vehicle plug and the bulb and gives the system the reading it expects. A decoder is not included in this pack. Plenty of vehicles need nothing at all and work the moment the bulb goes in. There is no way to know which camp yours is in until you try, so it is worth being prepared for either.
Fitting them without making life hard
Switch everything off and let the old bulb cool. A halogen bulb that has been running is hot enough to burn.
Take the dust cap off, unclip or twist the old bulb free depending on the holder, and unplug it. Put the new bulb in with clean hands, or gloves if you have them, holding it by the base. Keep fingerprints off the lens, because the oil holds dust.
Most HB4 holders only accept one position, but if yours allows any rotation, set the chips so they sit in the same plane the housing was designed around. Plug in, test before you close everything up, then refit the dust cap properly. That cap is doing real work given the IP60 rating.
Do the second side straight away. Anyone hunting for the best hb4 led conversion kit is buying a pair for exactly this reason, and leaving one halogen in place defeats the point.
Looking after them
LED bulbs ask for very little. Keep the fan opening clear, because a fan choked with dust cannot shift air. Keep the housing sealed and the cap on. Wipe the body with a dry cloth if it needs it, and never soak the bulb or spray it directly.
If you keep a spare, leave it in the box and store it somewhere dry. Loose bulbs in a boot pick up knocks on the lens and grit in the fan housing. People who buy the best led bulb with cooling fan for a project vehicle often grab a second pair at the same time, and boxed storage is how that spare stays usable.
The short version
This is a pack of two LED headlight bulbs with the HB4 fitting, also known as 9006. The colour is 6000K, the cooling is a fan built into the body, and the ingress rating is IP60, meaning dust tight with no water rating.
Check the code on your old bulb, check the room behind the housing, and be ready for the possibility that your vehicle wants a CANbus decoder, which is not supplied. Most importantly, remember what this set is for. It is sold for off-road, show and private property use, and not for use on public roads in headlights designed for halogen bulbs. If that fits how you intend to use it, the HB4 9006 LED headlight bulbs are a simple, tidy swap.