Yellow light vs white light in fog

Yellow vs White Light in Fog: Myth vs Reality

When it comes to lighting in foggy conditions, there has long been a debate about whether yellow or white light is more effective. This discussion is often influenced by the theory that shorter wavelengths scatter more than longer ones. This principle, known as Rayleigh scattering, was established by British scientist Lord Rayleigh in 1871 and explains phenomena like the blue colour of the sky. When sunlight passes through the atmosphere, shorter wavelengths such as blue and violet scatter more, making the sky appear blue.

Applying this theory, one might assume that longer wavelengths, like red or yellow, would penetrate fog more effectively. Red, however, is associated with traffic signals, so yellow became the preferred choice for fog lights historically.

The Science Behind Fog Scattering

While the logic might seem sound, it doesn’t apply to fog. Rayleigh scattering is only relevant for particles smaller than the wavelength of light. Fog droplets are much larger, meaning they scatter light in a wavelength-independent way. In other words, fog affects all colours of visible light equally.

Practical Evidence from Vehicle Headlights

You don’t need a physics degree to understand this. Simply look at car headlights. Designers have long known there’s no special colour that cuts through fog better. That’s why the majority of headlights are white, and regulations—such as those in the European Union—mandate white headlights for all new vehicles. This practical approach aligns with the scientific understanding that colour doesn’t matter for fog penetration.

Conclusion

For light to effectively penetrate fog, the colour—whether yellow or white—makes no difference. Both are equally effective (or ineffective) in such conditions. So, when choosing lighting for fog, focus on brightness and beam design rather than colour.