Remember that yellow lenses or yellow film are really just a filter that lets yellow light through, i.e. it blocks the rest of the spectrum. So, the light is dimmer overall.
Yellow improves perceived contrast to the human eye, and is less dazzling to oncoming traffic, so those components of the light do work ok. Not so much for actually illuminating things.
A true-yellow bulb color is definitely the way to go, if possible.
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