Hid in winter months?
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dirtydog is right on point here, but the reason yellow lights do better is because the longer wave length cuts through fog with less refraction back to you. The lower you go on the kelvin scale the longer the wavelength of light is, conversely the higher you go, into the more blue end of the spectrum, the shorter the wavelength and the more glare back you get from refraction. Hella knows this and sells yellow bulbs for just this purpose. I've also heard good things about the hella yellowstar bulbs.