Headlight bulbs: what H7, H4, H11 mean (and how to avoid mistakes)

Headlight bulbs: what H7, H4, H11 mean (and how to avoid mistakes)

When you are looking for a "headlight bulb," what you are actually buying is a standardized reference (the type/base). In Portugal and Europe, the most common are H4, H7, HB3/HB4 , and in many cars also H11/H8/H16 (often in fog lights).

1) H4 vs H7: simple difference

  • H4 : typically provides both low and high intensity in the same bulb (dual function).

  • H7 : This is usually a function (medium or high, depending on the car).

If you swap an H4 for an H7 (or vice versa), it won't fit — and even if it did, it wouldn't perform its function correctly.

2) H11/H8/H16: commonly used in fog

In many models, the fog lights use different bases than the low/high beam headlights. Therefore, check the owner's manual or look at the old bulb.

2) Brightness vs. durability: how to choose "your" light bulb

In the market there are generally 3 "families":

  1. More brightness/range (ideal for road use)

  2. More durability (for those who drive a lot in the city)

  3. White effect (more "LED" aesthetic)

Ideally, it should be aligned with its intended use:

  • Do you drive a lot at night? → Favors range and contrast

  • Urban driving, lots of on/off switches? → durability

  • Do you want a white look? → Choose white without sacrificing beams.

3) Certification and standards (why it matters)

For filament (halogen) lamps, there is UNECE regulation R37 , which defines requirements for approved lamps for use in approved optical units.

In practice, this translates to:

  • Correct filament focus → correct beam

  • Intensity within expectations → less glare

  • approval markings (when applicable)

4) Installation: details that prevent failures

  • Swap in pairs (left + right)

  • Do not touch the glass (oils can reduce its lifespan).

  • Check the headlight seal and cover (moisture kills bulbs).

  • After the replacement, confirm beam alignment/height.

5) Purchase checklist (headlights)

  • Confirm reference (H7/H4/H11…) by manual/old model.

  • Buy 2 units (pair)

  • Avoid "extra watts"

  • Prefer brands with clear information and compatibility tools (Philips/OSRAM).

FAQ

Can I use a "stronger" (higher wattage) light bulb?
Not recommended: it overheats and can damage the optics/connectors.

Is it worth switching to "+X%" (brighter) bulbs?
For those driving at night, usually yes — provided the reference point is correct and the beam is good.