A lighting system to simulate a window open to the sky and comprising an optical system including: a visible optical source, which emits visible optical radiation; and a chromatic optical device, which includes a diffusion region and defines a first emission surface arranged downstream of the diffusion region. The chromatic device receives the visible optical radiation and generates, on the first emission surface, a visible output beam, which has an angular luminance profile that exhibits a peak with FWHM below 20° in two planes, mutually orthogonal and containing the direction of maximum luminance. In each point of the first emission surface, the visible output beam comprises a direct component, emitted in the direction of the luminance peak, and a diffuse component emitted at angles that differ by more than 40° from the direction of the direct component. The CCT of the diffuse component is at least 1.2 times higher than the CCT of the direct component. The lighting system also includes an infrared source, which defines a second emission surface and emits, downstream of the second emission surface, an infrared output beam substantially without visible components.