How we tested them

AS the performance level of bulbs gets ever higher, we have made our test harder in order to find a winner among what are often very closely matched performers.

The heart of this test is the light on the road, this time from the doublefilament H4 bulbs (covering dipped and main beams in one) in a Nissan headlamp. We’ve kept our formula using light measurements at 50 and 75 metres, but these depend on alignment. We measured the amount of light that was more than 20 lumens to get a rating independent of alignment, plus the brightest spot.

As in our tyre tests, we converted the results to percentages to accurately reflect the differences between the bulbs, with the winner ranked at 100 per cent and the rest getting percentages relative to the top bulb’s performance. The results are based on an average of two bulbs that we bought or picked from multiple packs.

We also checked maximum light output to ensure that the bulbs were within the limit of the EC regulations. Prices given are for a pair of bulbs from online sources, but cost had a small part to play in this safety-critical assessment.