[![photo of race car in Le Mans][1]][1]

In Le Mans, all cars have 3 lights on the side.

The color part is easy: It is the color of the series you are racing in.

But sometimes 1 is lit, other times it is 2 or 3.

What is the logic of those lights?

  [1]: https://i.sstatic.net/p9ZZe.jpg