What two ideas are used to describe the motion of light?
Depending on the experiment we do, light sometimes behaves like a wave and sometimes like a particle.
In truth, light is simply light, and these are useful metaphors to help us understand its behaviour.
Reflection can be explained with either a wave or particle model.
Refraction can be explained with either, but it turns out a wave model better explains the velocity changes.
Young's double slit experiment (diffraction and interference) is better explained by a wave model.
The photoelectric effect cannot be explained by a wave model, only a particle model.