  The linear stability of a finite-depth algal suspension is investigated
numerically with particular emphasis on the effects of angle of incidence. The
suspension of phototactic algae is uniformly illuminated by both diffuse and
oblique collimated irradiation. The bioconvective solutions show a transition
of the most unstable mode of disturbance from the stationary (overstable) to
overstable (stationary) state at the variation in angle of incidence for fixed
parameter ranges. Furthermore, a transition from mode 2 to mode 1 instability
is noticed for some parameter values as the angle of incidence varies.
Oscillatory modes of disturbance are also predicted at the increment in angle
of incidence (or cell swimming speed)
