Headlight bulbs - what types are there and which is best?

There is a baffling array of different aftermarket bulbs to choose from today, with prices ranging from a few quid to more than £35. So here we consider whether it’s best to go for the latest, extra-bright bulbs, longer-lasting bulbs or bulbs with a whiter light output, or whether you should simply buy the cheapest ones you can find.

There are three different types of headlight bulbs: halogen (which is based on the technology that has been around for decades), xenon (which uses newer technology to create longer-lasting, brighter light) and LED, which is the newest, most energy-efficient type of automotive light. 

Car design generally dictates what type of bulbs are used. Smaller, more affordable cars are most likely to have halogen headlight bulbs, while those with sportier styling will be designed to have narrower headlight units, so they’re likely to use xenon bulbs.

Although the latest LED bulbs are widely used for daytime running lights on new cars, as headlights they’re still mostly reserved for range-topping, luxury and sporting models, because they’re the most expensive to produce.

Halogen bulbs

Although the basic technology behind halogen bulbs has been around for more than half a century, they’re still widely used, because they’re the cheapest to produce and replace.

Halogen bulbs use a tungsten filament, similar to that in a household bulb, but are filled with halogen gas, which helps the filament glow brighter and last longer. The H4 is a double-filament headlight bulb that’s typically used in small cars. The H17 and H18 bulbs are smaller, more powerful halogen bulbs, while the H8, H9 and H11 are self-sealing bulbs that don’t have to sit inside a watertight unit, so they’re often used as foglights.

Typical life expectancy: 2000 hours

Xenon or high-intensity discharge (HID) bulbs

Xenon bulbs, also known as high-intensity discharge (HID) bulbs, have an arc instead of a filament between their two electrodes. By law, it has to be working at 80% capacity within four seconds of being turned on, so it needs a high-voltage starter to ignite the gas and a control unit to keep the bulb alight. Although xenon is the gas that’s used to start the arc, it’s metal salts that keep it alight.

Until recently, most cars with xenon lights also needed headlight washers and a self-levelling mechanism to keep the light beams projected downwards no matter how heavily loaded the car is. This makes them pricier to produce – the main reason why many car makers stuck with halogen for so long.  

However, bulb producers have now managed to produce xenon bulbs that have a lower light output and therefore don’t need a self-levelling system or lens washers, making them about half the cost. So now we’re seeing them offered on a growing number of smaller cars and cheaper trim levels.

Although xenons generally last much longer than halogen bulbs, their light output can decrease over time, so eventually they won’t emit enough light to be safe for night use. Some manufacturers therefore recommend replacing xenon bulbs every three years.

Typical life expectancy: 10,000 hours

LED bulbs

LED lights are now replacing xenons on new cars, because they are more energy efficient, last longer and allow car makers to create signature light shapes.

In LED bulbs, electricity is passed through one or more light-emitting diodes instead of a filament or arc. The light produced is similar in brightness to that of a xenon bulb, but LED bulbs don’t produce excess heat, so they’re more efficient and therefore cheaper to run.

One concern is that if the electronics in an LED bulb fail, in general the whole light unit will have to be replaced, which will be very expensive and therefore impractical when cars are older and worth much less. However, there are already some LED bulbs that can be replaced separately, rather than needing to be soldered into place inside a light unit.

Typical life expectancy: 30,000 hours

Next: Why are more people being dazzled by car headlights? > 

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