We tested the low-beam performance of single-filament (9003) and dual-filament (H7) bulbs from GE, Hella, Philips, and Sylvania, and PIAA's dual-filament bulb. We also compared their performance ...
The answer would be a combination of the right filament material and using an evacuated bulb to prevent the filament degrading. But it took over a century to get a commercially successful lightbulb.
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