Does the propagation of light through spacetime, with regards to how we describe it, depend on when a photon is a wave function or point particle? When for example, a photon is emitted from an atom, does that photon propagate through spacetime in all directions away from the atom in the form of a sphere (Wave Function) and then at some point along its propagation it is absorbed, reflected or refracted (detected) and at that point do we then consider it a Point Particle?
 A: A photon is effectively a wave until it is detected.  The classical two-slit interferometer, used with light so dim that only one photon is present in the apparatus at a time, shows that each photon's wave function passes through both slits - which is inconsistent with the photon being a point particle during its propagation.  However, the wave function only has spherical symmetry if it is emitted from an infinitesimal point.  In the case of the two-slit interferometer, the part of the wave downstream from each slit has approximately the form of a cylindrical wave.
A: A single photon gets emitted in a specific direction.  Example, a pebble dropped in a pond but the pebble was dropped in the middle of 3 logs in a "U" shape, thus the wave is directed and this is a good analogy for the photon.  But the wave is still spreading out and can be affected by many other objects in the pond.  Why the photon/atom behaves this way is likely because of the interaction with the other electrons or nucleus of the atom when the photon is emitted.
A photon can interact with objects it passes close too, this is diffraction, it changes the direction but the photon wave function is the same.
A photon can be refracted or reflected, the wave function is destroyed but immediately replaced by a new one as the electrons do the work.
You can consider the photon a point particle in many experiments/explanations, ex why is one light brighter than the other, i.e more particles.  The use of the particle explanation is widely used.  You can consider the photon a wave when your are studying its propagation, diffraction patterns etc.
Like water you would typically use the particle explanation when its raining or the wave explanation to explain for example a tsunami.
