So I am not an expert and recalling what I have read in several books and articles, but the conditions of fusion necessary to create photons only exists in the core of the sun. It was a mystery to us and we did not know until scientists were able to use quantum mechanics was able to explain the mechanism, it requires enough temperature and gravitational pressure to force subatomic particles close enough to overcome the forces that ordinarily keep them apart, and this only happens to a small percentage of meeting nuclei with quantum tunneling explaining how they overcome the forces that want to keep the nuclei apart - there's just so many particles squeezed close together that a small percentage that meet (possibly easier to visualize as the quantum wave function describing the position) fuse. This is also why we cannot use this method of fusion on earth - it's impossible to do on earth barring some sci fi artificial gravity invention. If this were not true and fusion could take place anywhere on the sun, the sun could rapidly use up all of the fuel of hydrogen. I am simply repeating what I have read - each photon has to make its way to the surface of the sun after many collisions, since the direction is random and not always outwards, it is theorized they just ping pong back and forth for x years where x can be hundreds of thousands of years. Here's the clearest explanation I found though they only use one slide on the photon's drunken walk https://svs.gsfc.nasa.gov/11084