Don’t be tempted to save cash on unbranded alternatives. For top D3S performance it has to be the Philips, and Ring is our standard choice. There are no bad H4 bulbs here, but the RacingVision is our choice. The Figure of Merit for HID is close to double that of the halogen, with a beam that’s 30 or so metres longer. Running both tests at the same time, although in different headlamps, gave us a chance to see just how big an advance HID was over halogen when it was introduced over 20 years ago. It came as no surprise that both samples failed to reach the minimum light levels by a significant margin. It finished last in all our tests and delivered just 16 per cent of the area above 30 lux compared with our winner – easily visible to the naked eye. This is an Amazon best seller in faux-Osram packaging, but even at this super-low price, it’s too costly. When some producers’ prices top £160, it’s tempting to save some cash by going for an unbranded alternative. The best H4 car headlight bulbs Philips RacingVision GT200 The results were converted to percentages and added together to get our result, with the winner rated at 100 per cent and the others scored relative to that performance. The prices quoted are for a pair of bulbs. We also checked light output to ensure that the samples complied with ECE regulations. Our figure of merit (FOM) was also calculated using levels at 50 metres in front of the car on the kerb and in the centre of the road, plus twice the hard-to-reach 75-metre roadside mark. We measured the area of the beam at more than 30 lux, beam reach above three lux, plus the brightest spot. The tests were the same for both types, despite the different light sources: filament for the halogen and an arc between electrodes for HID. It’s an unusual, if not unique, set-up, but the results have been corroborated by tests at parent company Osram’s conventional light tunnel in Germany, which we have used in the past. Software then measures the light at various points in the beam. Bulbs are placed in a headlamp - a reflector type from a Fiat 500X for halogen bulbs, projector from an Audi A3 for HID - allowed to burn in to settle output, then an image is taken of the beam pattern on the wall.
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