English: Supplementary Movie 1 It shows the directed motion of a dilute suspension of synthetic photo-active microparticles (2.7 μm diameter) in a light profile with period length L = 33.5 μm, segment length ratio a/b = 0.22 and modulation amplitude ΔI = 1.0 μW/μm2 (top), 0.7 μW/μm2 (middle), 0.2 μW/μm2 (bottom). Under the imposed light field, the active colloids align with the +x-direction. At smaller amplitudes ΔI, the degree of alignment decreases, which leads to a reduction of the directed motion. Moreover, as visible in the movie, around the minima of I(x) the particles perform a back and forth motion due to opposite torques. With increasing ΔI, the velocity variations become smaller and an almost steady particle motion is observed. The movie is in real time.