Method for measuring external light to control protection means against sunlight or illumination

The invention concerns a method which consists in detecting and discriminating at least three states, respectively blue sky, white sky and direct sunlight. The discrimination between the three states is based, for example, on an intermediate detection distinguishing between either a homogenous state or a nonhomogeneous state of the sky. White sky means a sky saturated with humidity, with strong light diffusion and producing a high level of brightness. The method can be implemented, for example by using sensors or a monochromatic or color camera.