  Based upon recent experiments in which Janus particles are made into active
swimmers by illuminating them with laser light, we explore the effect of
applying a light pattern on the sample, thereby creating activity inducing
zones or active patches. We simulate a system of interacting Brownian diffusers
that become active swimmers when moving inside an active patch and analyze the
structure and dynamics of the ensuing stationary state. We find that, in some
respects, the effect of spatially inhomogeneous activity is qualitatively
similar to a temperature gradient. For asymmetric patches, however, this
analogy breaks down because the ensuing stationary state is specific to partial
active motion.
