Always replace my standard white fog lights with yellow halogen bulbs or LED !! High intensity halogens H-11 for the GLA 250 !! My Corvette takes LED's and my Honda Ridgeline also takes H-11 halogens ... Yellow, Yellow and Yellow !!! Even use Yellow Halogen Headlamps on the Ridgeline !!! But, then again I live in Portland Oregon ... City of Rain !!!
Fog lamps aren't supposed to be less output of light, just a warmer color and lower to the ground. The bluer the light the more it scatters and when dealing with fog you have enough scatter already. So you can put in yellow HID, add 12 more and you'd be great - in fact better than stock. The halogens are pretty warm color already, by going with a blueish white of normal LED or HID you lose effectiveness for their intended purpose. Though honestly I've not had to use fog lights for fog more than one time in over 20 years now. Normally I consider them driving lights and love the way they spill light onto the sides to illuminate shoulder etc. So color is irrelevant.
That's exactly what I use them for as well. I even went as far as fitting in bulbs as bright as my headlights in them, 6000k headlights, 6000k fogs. It was part cosmetic and part real need, but not a burning need.
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