My 2003 Opel Agila has H4 combined full and dipped beam headlight bulbs which are completely useless in the dark. It is really hard to see anything on the dipped beam. They do not seem to be very bright, but the garage replaced both sides at the MOT in November for £10 in total (about $14). I don't know which brand bulbs they are, they just seem to be generic. I know they are halogen.

I do a lot of night-time driving, so I need my headlights to be bright so I can see, but at the moment the dipped lights seem to be very dim and do not light up very far ahead, even the adjustment knob is at 0, which is at their highest position.

I looked into Xenon headlights, but as I have no headlight washers these would be illegal. I also do not want to blind other oncoming drivers, as that is incredibly dangerous and selfish.

Are there any legal upgrades that I can do to make my headlights brighter?

  • 3
    I buy the offroad halogens in the US. 50w low beam and 55w high beam is the max here. I get 65w low and 110w highs. It's illegal though. Mar 1, 2016 at 22:59
  • Like @DucatiKiller - Just ensure you change them back out for your MOT and hope the Polizei don't catch yah! :o) Mar 2, 2016 at 0:41
  • 1
    Are your lenses clear? If the lenses are old, they will really reduce the light levels that they pass. However, that can be easily fixed. mechanics.stackexchange.com/a/11883/57
    – Bob Cross
    Mar 3, 2016 at 15:16

4 Answers 4


It is possible that the adjustment is not correct, i.e. the lights are still shining too steep down though the knob is set to 0. Though you can test this on your own, shops will do this with more precision. It doesn't cost much and may be for free.

DucatiKiller suggests high-power bulbs in his comment.
From the legal side (they're for sure illegal in the UK, too), I think the bulbs will never be inspected, but you may still get into trouble. Imagine someone says the crash happened because he was dazzled by your lights...
From the technical side, make sure relays and cables can handle the higher current, an the headlight can handle the increased heat from this bulbs. 65W instead of 50W may be OK, but 110W instead of 55W is quite much.

But there are also legal brighter bulbs out there like for example Osram Night Breaker. Compared to a generic bulb, they claim to give more than twice the light, 40m wider range and 20% more white light (Now, how to measure that???)

This are of course advertisements, and the numbers are suspicious. But to my experience (and many others on the web), they indeed give brighter and more white light. If it's twice the light? Hmmm, not sure, but definitely more. Here is a german blog showing pictures with standard and this bright bulbs.

This bulbs are legal and have no technical issues because they have the same power as generic bulbs. But they also have two disadvantages: They are really expensive, and their life time is typically just about 50% of generic bulbs. The reason is, to get more and more white light out of a bulb with same power, the filament must be hotter. But hotter filament drastically decreases life time.

Finally, you mentioned Xenon lights. It's not that simple to convert normal lights to Xenon lights. You do not only need headlight washers, you will also need an automatic adjustment, and the headlight must be made for Xenons. There are many illegal conversion sets out there. I guess Xenon is usually only an option if the car is available with Xenon from the manufacturer.

  • LED may also now be a viable solution as the 55w legal limit is the limit of consumption and not how much energy is allowed to be output. LEDs at 55w (if available) should be substantially brighter than a filament bulb at 55w
    – Mauro
    Mar 2, 2016 at 10:04
  • 1
    @Mauro: Oh yes, and 55W LED would equal to a halogen bulb of somewere beyond 250W... I also don't know what's the legal limit for brightness, it seems, defining limits by power is a bit outdated today. However, it's still valid at least for lights using filament bulbs. (btw: I'm really curious about the LED Matrix light advertised today. It consists of several LEDs, the car recognizes opposing traffic, and switches off only those LEDs which would dazzle them.)
    – sweber
    Mar 2, 2016 at 10:24
  • @Mauro the issue with substituting a LED "bulb" is that the housing design probably assumes a different (smaller) light source, as a result the light pattern may be seriously degraded with LEDs.
    – dlu
    Dec 18, 2016 at 16:41

Seeing as you are in the UK - the legal options for aftermarket headlights are given on the Department of Transport website:


In summary it states that according to the letter of the law all aftermarket HID upgrades are illegal.

However, it goes on to admit that the law hasn't caught up with technology. It states that any system certified compliant to the EU regulation ECE98 is acceptable.

In other words, to answer your question, are there any legal upgrades - it depends!

So as Dickens' Mr.Bumble famously said, "The law is a ass - a idiot".


In the case of old vehicles, the dim lights might be an outcome of corrosion on the wiring for the lights and wear in the switch contacts. Headlight relay kits are available that use the existing wiring to switch the relays and draw power directly from the car battery or another source. I haven't looked but I expect that there's kits specced to allow you to put higher power bulbs in but that would still be limited by how much heat the headlights can handle.

The kits seem to start at about £5 on eBay but I've no idea of the quality of them.

The kits don't require any changes to the headlight or bulbs and the connectors all fit straight onto the existing headlight connectors so there won't be a problem at the MOT.


There are a few maintenance checks that you should make before embarking on a modification program:

  1. Check that the lights are aimed correctly. This will be an under the hood adjustment, not an adjustment of the headlight leveling control. A quick check is to pull up about 10 meters away from a wall on a level surface and turn the lights on. The beam should hit the wall at about the same height as the headlights and should be parallel to the axis of the car (straight ahead, not off to the side).

  2. While you're at the wall check that the in-car adjuster is actually working.

  3. Inspect the condition of the light fixtures themselves. The reflectors should be clean and shiny. The lenses should be clear without significant scratching or yellowing. If they are not clean and clear with a bright reflector, either replace them or try polishing the lenses.

  4. Verify that you've got adequate voltage at the lights. To do this you'll want to "back probe" the connectors at the lights while the lights are on, so that you can see the actual voltage drop under load.

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