  In this study, our focus is mainly to check the effect of light scattering on
the onset of thermal-phototactic-bioconvection in an algal suspension where the
suspension is illuminated by the collimated oblique irradiation from above
while simultaneously applying heating or cooling from below. We conduct a
numerical investigation into the linear stability of a suspension containing
phototactic algae, focusing particularly on how the angle of incidence of
oblique collimated irradiation influences the system. Our solutions reveal a
transition of the most unstable mode from a stationary to an overstable state,
or vice versa, under certain parameter configurations as the angle of incidence
varies. Additionally, we frequently observe oscillatory instabilities in cases
where the upper surface is rigid, particularly as the angle of incidence
increases within the suspension.
