  We characterize two-dimensional (2D) microtubule-based active nematics driven
by light-responsive kinesin motor clusters. We assess two constructs of
optogenetic kinesin: opto-K401, a processive motor, and opto-K365, a
non-processive motor. Measurements reveal an order of magnitude improvement in
the contrast of nematic flow speeds between maximally- and
minimally-illuminated states for opto-K365 motors. Focusing on opto-K365
nematics, we characterize both the steady-state flow and defect density as a
function of applied light and examine the transient behavior between
steady-states. The steady-state nematic flow and defect densities are set by
the applied light intensity across centimeter-sized samples, independent of
initial conditions. Although nematic flow reaches steady-state within tens of
seconds, the defect density exhibits transient behavior for 4 to 10 minutes,
showing a separation between small-scale active reorganization and system-scale
structural states. This work establishes an experimental platform to test
theoretical frameworks which exploit spatiotemporally-heterogeneous patterns of
activity to generate targeted dynamical states.
