Light curves extracted along the 3 horizontal white lines for two illumination patterns. Left column: 2D pattern from a point-like source in K_s band with R_diff = 300 km and R_ref ≈ 28 000 km. The modulation indices of the three light curves differ by less than 5% from the 2D pattern modulation index. Right column: the illumination pattern for an extended source with R_s ≈ 41 000 km, through the same refractive screen. The modulation indices fluctuate by more than 30% around the 2D pattern index, implying the necessity of longer light curves for a better statistical representativity. The distance scale is common to both patterns. The circle shows the projected star disk. The 3 light curves from the right column are not completely decorrelated, because of their common proximity to the same large positive fluctuation.