How to make the illumination dimmer somewhere, but also brighter somewhere else? Redirect some or all photons – use a mirror, a prism, a lens. These all ensure the photons end up somewhere else.
More photons arriving: it's brighter. Fewer photons arriving: it's dimmer. But can you predict how putting things in the space around the source affects where the photons end up?
Let's set up a way to figure out how the photons get to explore their space and from that predict where they'll show up – so where it is bright or dim. (Although people say that
photons explore all paths, that's simply a way of describing the calculations to be done: no-one knows what the photons really get up to between source and detector.) Then show how this description predicts where it will be light or dark, still representing photons according the best available model.