Retro-fit super-bright gas discharge lights are available for a growing number of cars. But, for most of us, the best way of improving visibility in the dark is to fit brighter headlamp bulbs.

The difference between the best and worst bulbs is huge – some of the latter even failed to meet European regulations. We concentrated on the twin-filament H4 in a real-life test, where we didn’t readjust the lamp unit after fitting each of our 30 samples. Our results were based on the average beam from a pair of bulbs.