You've probably already noticed that many of the French classics (and beyond) used yellow headlights instead of the white/yellow light. And contrary to what you might think, it's not for aesthetic reasons.
The story goes that, like the yellow headlights that differentiated French military vehicles from German ones, the French government also wanted to differentiate their cars on the road — which is not entirely true. To find out the real reason we have to go back to the 1930s of the last century.
In November 1936, a law came into force in France that required all motor vehicles to be equipped with headlamps that emit yellow light — “selective yellow”.
Why yellow headlights?
The reason was simple: according to a study by the Académie des Sciences, this light caused less glare than white/yellowish light, especially in weather conditions unfavorable to driving (rain or fog).
From the following year, all cars registered in France — and even imported ones — started to use yellow headlights.
Yellow headlights were even more effective and were always preferred for driving in poor weather conditions such as fog or rain.
The secret is in the way the human eye processes different types of light. White brings together all colors, and blue, indigo and violet are those with a shorter wavelength. They are, therefore, the most difficult to process, in addition to causing more shine, which leads to dazzling.
Removing these tones we obtain a yellow light, which, for the same intensity, has less brightness, thus facilitating our eyes' task.
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On the other hand, several studies in the second half of the 20th century — mainly a study carried out in the Netherlands in 1976 — concluded that in practice there were not great differences in visibility between the two types of light. It was found that the intensity of the yellow light beam was lower and this contributed to the feeling of less glare on the part of the drivers, and not necessarily a better visibility.
The truth is that automobile lighting at the time was not famous, regardless of whether the light was white or yellow. Like everything else, lighting evolved over the years and, pressured by the European Union, which wanted to standardize the legislation, France started to adopt white lights in 1993 instead of selective yellow, following the example of other European countries .
Today, yellow headlamps are banned in France, with the exception of vehicles registered before 1993 or when it is just fog lamps. And in the GT’s at Le Mans…
