A quick guide to car headlight bulbs

Light-emitting diode (LED) bulbs

While LED lights are more commonly used in taillights, they're starting to be used more and more on newer cars now.

As LEDs are semiconductors with no wear-and-tear components, they should technically last as long as the car. As well as looking great, they require less energy than halogens – cutting the car's energy consumption and thus CO2 emissions – and put less strain on the battery. The light they emit also mimics daylight, which causes less glare and prevents fellow drivers from being dazzled.

But because they don't emit much heat, the lenses can frost over during the colder months, which impacts light output.

High-intensity discharge (HID) or xenon bulbs

HID or xenon bulbs produce light through an arc of current as opposed to a metal filament. They're often factory fitted on family and mainstream cars, or retrofitted in an upgrade. While HID conversion kits are quite cheap, to be road legal you need a complete unit including self-levelling and cleaning systems.

Xenons do have a longer lifespan than halogens, though, at around 10 years.

Halogen bulbs

Halogens are the traditional option and the lowest cost. There are three ways you can upgrade them, however:

• 'Brighter' bulbs which claim to emit between 30% and 100% more light.
• Energy-saving bulbs which last longer and cut the car's energy usage.
• Blue (or xenon-effect) bulbs which produce a blue-tinged light and are mainly used by drivers for cosmetic reasons.

So which headlight bulbs should you go for?

After carrying out a series of tests, Which? found the xenon bulbs outshone 'brighter' halogen bulbs and scored full marks for dipped beam and main beam performance. However, xenon lights did cut off sharply at greater distances, recording no light reading on dipped from 75m away. The majority of halogen bulbs did produce at least some light from this distance.

On main beam, xenons were only a quarter as bright from 25m away as they were from 10m away. The upgraded 'bright' halogens were still 80% as bright, though still dimmer than the xenons.

They do perform better than halogens in general, but drivers have to pay for that privilege. So, the advice is to read product reviews carefully and choose bulbs tailored to your driving habits – for instance, opt for improved long-range light if you regularly drive in the dark.

Headlight maintenance tips

• Keep your headlights clean to ensure maximum brightness when driving in the dark or fog.
• Always upgrade bulbs in pairs, because if one light is out, chances are the other one will soon follow.
• Behind the wheel, you might not notice a blown bulb, so carry out regular checks while the car is stationary. Reduced brightness indicates a bulb has blown or is on its way out.
• If your indicator lights are blinking faster than usual, you could have a blown bulb.

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