Car bulb types and the law

Modern LED bulbs emit a brighter, longer-lasting light than traditional halogen car bulbs. LED lights are packed full of light-emitting diodes. When electrons pass through, the semiconductors inside transform the power into light.

LED bulbs are highly energy-efficient, drawing a lower wattage from your car battery and have a longer lifespan than halogen bulbs. They also provide a warm and intense beam that can be 150-300% brighter than a typical halogen bulb.

You’ll find that LED bulbs can be more expensive than other car bulb types, but that’s offset with the thousands of hours of trouble-free operation you can expect. A LED bulb can last up to 10 years.

If LED lights are energy-efficient, highly effective and a worthwhile investment, what’s the catch? Well, it's currently illegal to fit LED bulbs to your car unless your car’s manufacturer has installed them. The reason is that no legislation currently exists to approve the use of LED lights as a replacement for the typical halogen lights you find on most vehicles.

LED bulbs are perfectly legal for both interior lights and for off-road use.

Halogen bulbs (sometimes called filament bulbs) are the classic car bulb design that we’re all familiar with. The humble halogen bulb contains a tungsten filament that gets hot and creates light when a current passes through it. The bulb is filled with halogen gas to prevent them from discolouring.

Most cars come fitted with halogen bulbs because they’re more cost-effective to manufacture and therefore cheaper to replace than other bulb types. Swapping out a like-for-like bulb can be done in a few minutes, either by you or through our expert fitting service.

All halogen bulbs are tested and road legal. You’ll also find that halogen replacement car bulbs are cheaper than LED lights or xenon bulbs. Longer-life halogen bulbs are available and can provide a 25%, 50% or 3 x improvement in operating life for a small cost increase per bulb. If you want brighter lights, our Halfords Advanced range delivers up to 150% more light from the same size.

Xenon HID bulbs use an electric arc between two electrons within the bulb to create a much stronger light than a typical halogen bulb. The inside of the bulb is filled with xenon gas, which produces a much brighter light than a halogen bulb.

While they’re more expensive than halogen or LED bulbs, Xenon HID bulbs can produce 300-450% more light than a standard halogen bulb and come in a range of colours. We recommend replacing them every three years, and in pairs, even if they don’t appear to have failed.

Xenon HID bulbs aren’t a slot-in replacement. Instead, you’ll need some additions to fit them. Like LED lights, Xenon HID lights are only road legal for cars where they were originally fitted by the manufacturer.

Halogen bulbs use a filament to generate light and are the traditional form of car bulbs that come fitted to most vehicles. LED bulbs use diodes to generate light and are a popular upgrade that owners can make to their vehicles. They last for longer, are more energy-efficient and emit a stronger light than typical halogen bulbs.

These will often have a blue tint to them to make them appear brighter. Their output is too far away from yellow or white to be road legal, and so because of this, we mark them as off-road use only - in fact, the bulbs are not E marked to prevent this. These bulbs are intended for use at car shows or off-road competitions such as rallycross (although rally cars may still be subject to road regulations).

Halogen infrared bulbs, more commonly known as HIR bulbs, are similar to halogen bulbs. However, HIR bulbs have an infrared coating that reflects heat back to the filament, ultimately creating a brighter light of around 2500 lumens for the same or less energy as other types of bulbs.

HIR bulbs are more expensive than their halogen counterparts due to their complexity, but are necessary – avoid the temptation of going for the 9004/9005 as alternatives which won’t be anywhere near as bright or last as long. Their small size makes them the ideal fit for most cars. Most Vauxhall/GM cars from 2009 and the Toyota iQ are the most common cars using HIR bulbs, although this is likely to increase as the technology gains popularity.

The colour temperature of a bulb describes how yellow or blue the bulb is. The colour temperature is measured in units called kelvins. If the bulb has a low colour temperature (2500K for example), it will be more yellow. If the colour temperature is higher, it will be bluer. Most car bulbs, such as the H7 477 Car Headlight Bulb Halfords +25 per cent Longer Life Single Pack, will produce a pure white light.

One additional requirement is that the bulbs must be fitted with an appropriate projection lens. The Department for Transport says: '...the entire headlamp unit must be replaced with one designed and approved for use with HID bulbs and it must be installed in accordance with the rules stated above.' In practice, this would mean either replacing the whole headlamp cluster to an HID-compatible projector or fitting an E-marked aftermarket projector lens.

UPDATE: As of the May 2018 MOT inspection manual, any car which has had an aftermarket kit fitted without the correct projection unit and lens unit being replaced as well as an immediate 'Major' fail. Previously this wasn't always enforced, but a concerted effort to ensure this rule is followed means there is a potential for many more fails. Due to this, we can't make any comment on aftermarket kits.

Lastly, the MOT guidelines require that the bulbs must turn on every time - immediately - the bulbs must project a light which is either yellow or white (any other colour is a Major fail) and that both bulbs are the same colour; if one dipped bulb is yellow, and the other is white, this will be an MOT failure and illegal.

All of these issues are not something which Halfords can help with or provide equipment but may provide food for thought.