Your car's bulbs aren't just replacement parts you change when they burn out. They determine how well you can see the road at night, in the rain or fog, and how visible you are to other drivers.

In this guide, you'll learn how to find the right bulb code, the difference between halogen, LED and Xenon bulbs, and what to look out for to make sure your bulbs are road-legal!

Step 1: Find the bulb code you need

Each position in your car (low beam, high beam, fog lights, indicators, brake lights) uses a specific bulb type. The code, such as H7, H4 or W5W, determines its shape, base and wattage. There’s no room for “close enough”: if the code doesn’t match, the bulb simply won’t fit.

You can find the code in three ways:

• In the owner’s manual: there’s usually a table listing all the bulbs used in the car, under “Bulbs” or “Technical specifications”.
• On the old bulb: the code is printed on its base.
• On the headlight cover: many cars display it there or on the headlight itself.

Bear in mind that some cars use the same type for low and high beams, while others use a different type for each. Some cars, such as those with H4 bulbs, use one bulb for both.

Step 2: Choose a technology – Halogen, LED or Xenon?

Halogen bulbs

These are the bulbs fitted to most cars at the factory. However, they’re not all the same. There are four main categories:

• Standard: the basic option, offering a good balance of price and lifespan.
• Increased brightness (+100%, +150%, etc.): provide more light and a longer beam, but have a shorter lifespan.
• Long Life: last much longer, making them ideal if you drive a lot of miles or if replacing the bulbs in your car is difficult.
• White light: provide a “whiter”, more modern light, closer in appearance to Xenon, while remaining approved halogen bulbs.

Advantages: Low price, easy installation, full compatibility with your car.
Disadvantages: Less light and a shorter lifespan than LED and Xenon bulbs.

LED bulbs

LED bulbs produce bright, white light, switch on instantly and use less energy. In newer cars, they often come as complete headlight units from the factory. There are also LED bulbs that fit in place of halogen bulbs (retrofit), but these require careful consideration.

Advantages: Very long lifespan, bright white light, low energy consumption.

Disadvantages: Higher price. Their legality in halogen headlamps is limited (see below). Some cars display an error message, so CANbus bulbs or adapters may be needed.

While the rules for main headlights are complex, LED bulbs for interior lighting, license plate lights and position lights are an easy and popular upgrade. Even then, check that the light is white and that the bulb is approved.

Xenon bulbs

Xenon (HID) bulbs produce very bright light and are found in cars with factory-fitted Xenon headlights. They can be identified by their code, which always starts with “D” (D1S, D2S, D3S, etc.).

Advantages: Very powerful illumination and a long lifespan.

Disadvantages: High price. They operate at high voltage, so replacement requires care or should be carried out by a garage. They are only suitable for cars with factory-fitted Xenon headlights.

If your car has Xenon headlights, replace the bulb with one with the exact same D-code. Since their colour changes over time, it’s best to replace them in pairs.

What do Kelvin and Lumens mean?

In bulb descriptions, you’ll see two numbers worth understanding:

• Kelvin (K): indicates the color of the light, not its brightness. Around 3,200K is the warm, yellowish light of a halogen bulb. Around 4,300K is the white light of factory-installed Xenon bulbs. 6,000K and above produces a cool white light with a blue tint.
• Lumens (lm): indicates how much light the bulb emits. This is the number that matters when it comes to how well you’ll see.

Higher Kelvin does not mean more light. In rain and fog, warmer light often provides better visibility than very cool white light.

Are LED and Xenon bulbs legal?

This is where the most common trap lies. On public roads, only bulbs with type approval are legal. Look for the E marking inside a circle, followed by a number (e.g. E1, E4). The approval must cover use in that specific position.

• Approved halogen bulbs: these are legal, including high-performance and white-light bulbs.
• LED bulbs used in place of halogen bulbs in headlights: most of those on the market are not approved for use on public roads, even if they fit properly. Only a few models are approved, and they usually come with a list of compatible cars. Before buying, check whether your car is on the list.
• Xenon kits in halogen headlights: these are not permitted. Halogen headlights are not designed for such powerful light and will dazzle oncoming drivers.

An unapproved bulb could cost you a fine during a traffic police inspection and a failed roadworthiness test. More importantly, it could dazzle other drivers.

Skroutz Tip: Before changing a bulb

• Replace bulbs in pairs. If one burns out, the other will soon follow, so you’ll have the same light and color on both sides.
• Don’t touch the glass of a halogen bulb with bare fingers. Skin oils create “hot spots” and shorten its lifespan. Use gloves or a clean cloth.
• Don’t install bulbs with a higher wattage than specified. They may overheat and damage the headlight or wiring.
• Check the headlight alignment after replacing a bulb. Even the best bulb won’t light the road properly if the headlight is misaligned.
• Keep a spare bulb in the glove compartment. It takes up very little space and saves you from driving with only one headlight at night.