If you're driving a 123 car, this is one of the weaknesses, and turning the dimmer all the way up will still result in barely enough instrument panel light to see how fast you're going. These lights are as bad as US Spec headlights on a 124 car.
I have put up with this over the years, but I suspect that there may be a slightly brighter bulb available. I have never bothered to check into it.
If you DON'T drive a 123 car, try to find the dimmer and give it a try.