I know that for body centered cubic structures the allowed reflections only happen if h+k+l is even and reflections are forbidden is h+k+l is odd, and for basic face centered cubic structures (excluding diamond cubic) for a reflection to happen the h,k,l terms must be all add or even and if they're a mix of odd and even then the reflection is forbidden.
I've tried looking in textbooks/lecture notes as to how/why these selection rules come about but I can't find an answer which explains, it's just kind of stated that this happens. Why is it that you get these allowed and forbidden reflections?
I know it'll probably be something to do with the group space/symmetry/destructive interference within the structures but I can't come up with a definitive explanation other than just stating that it's to do with 'symmetry' or 'destructive interference within the cube'. Is there a more detailed and specific answer that explains what actually goes on within the structure?