  The persistent motility of the individual constituents in microbial
suspensions represents a prime example of so-called active matter systems.
Cells consume energy, exert forces and move, overall releasing the constraints
of equilibrium statistical mechanics of passive elements and allowing for
complex spatio-temporal patterns to emerge. Moreover, when subject to
physico-chemical stimuli their collective behaviour often drives large scale
instabilities of hydrodynamic nature, with implications for biomixing in
natural environments and incipient industrial applications. In turn, our
ability for external control of these driving stimuli could be used to govern
the emerging patterns. Light, being easily manipulable and, at the same time,
an important stimulus for a wide variety of microorganisms, is particularly
well suited to this end. In this paper, we will discuss the current state,
developments, and some of the emerging advances in the fundamentals and
applications of light-induced bioconvection with a focus on recent experimental
realisations and modelling efforts.
