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Quick google : Some professor’s (Dr. Lawrence D. Woolf) take on yellow or longer wavelengths on fog penetration.
Summary : It probably isn’t true that yellow increases penetration.
With that said, really need to get some real life lux meter readings @ say 200m with a 3000K and a 6500K light in foggy conditions.
In addition to user’s ease of target acquisition + target definition.
edit - but don’t take my statements wrongly. Yellow fog lights could still be seen by other drivers better than headlights, mainly coz of beam pattern cut-offs and/or colour that kinda thingy. And if you are going to switch on both HID/LED headlamps + extra set of foglights, then yes.
It’s something like our hobby’s Aspheric lens crowd vs Reflector lens crowd for throw. Fog lamps have much more defined throwy beam patterns.
As for reflected glare of the beam through the air back to the user of a 3000K beam vs a 6500K beam, i really don’t know. The scattering effect theory is said to be used wrongly in this case. It might be due to eye fatigue or perceived glare or something, but i believe the effect is relatively small for 5000K and 6500K.