It is said that interference occurs when a peak (of the light wave) meets a trough and the wave cancels to zero, giving a dark band on the screen. However, if light waves are bands or "shells" of high densities of photons interspersed with bands of zero photons, then how can this be? When a peak meets a peak then yes, we get constructive interference (light bands). When a trough meets a trough there are zero photons (dark bands), but when a peak meets a trough then surely this is the mid point between light and dark with a "half" illumination. In other words, I do not see that destructive interference can occur with light since light is quantised. Can anyone confirm or refute?