1. A determination procedure of luminance of traffic signs comprising the following stages: a) obtaining a sequence of images at a frequency corresponding to a frequency of an electric grid such that the sequence of images are obtained at an identical point of a sine wave that characterizes an electric grid supply voltage, the sequence of images including a first image with a first illumination level and a second image with a second illumination level, the firsst illumination level corresponding to a stabilized base illumination and the second illumination level corresponding to the stabilized base illumination and an additional illumination, the sequence of images being obtained at a frequency of an electric grid such that the first and second images are obtained at an identical point of a sine wave characterizing a supply voltage from the electric grid; b) extracting a first region of the image corresponding to a sign represented in the image and extracting a second region of the second image, the second region corresponding to the sign represented in the second image; c) calculating a first luminance value of the sign using the first region, the first luminance value being the sum of luminance due to the stabilized base illumination L a , luminance due to the additional illumination L b and luminance due to uncontrolled ambient illumination L c , whereby the first luminance value L1 is 
 L 1 =L a +L b +L c , d) calculating a second luminance value of the sign using the second region, the second luminance value being the sum of luminance due to the stabilized base illumination L a and luminance due to the ambient illumination L d , the second luminance value L2 is: 
 L 2 =L a +L d , e) obtaining a luminance difference value of the sign corresponding to the first luminance value and the second luminance value L2, wherein, the luminance difference value ΔL obtained is the luminance corresponding to the additional illumination L b , 
 Δ L=L 1 −L 2 =L b , such that, the effect of the ambient illumination and the stabilized base illumination have been suppressed.