Light Switch

A closer look at Light Switch

Five squares, one decision

Each selection reverses the state of the chosen square and its immediate horizontal and vertical neighbors. A light that is on turns off, and a light that is off turns on. Diagonal squares are unaffected. A middle square changes five lights, an edge square usually changes four, and a corner changes three. The goal is a completely dark five-by-five board.

Why repeated moves cancel

Select the same square twice without resetting, and every light affected by that square returns to its earlier state. This is useful when you make an accidental move: selecting that square again reverses its effect, although both selections still count as moves. You do not need to press a square more than once in a planned solution.

Chase lights from the top

A practical first method is to look at the top row. For each lit square there, select the square directly below it. This clears the first row, because each of those selections affects the square immediately above. Continue row by row. The method moves the unresolved pattern downward; it does not guarantee that the bottom row will be clear on the first attempt.

Read the bottom row carefully

When you reach the bottom, do not randomly undo the work above. A remaining pattern tells you that a different starting choice in the top row is needed. Restarting and experimenting with one changed top-row choice can teach you more than rapid guessing. Our boards begin as all-off grids and are scrambled by valid switches, so a solution always exists.

Take it slowly

There is no time limit. Lit squares show a filled dot; unlit squares show an outlined dot, so the state is communicated by more than color. Keyboard users can Tab between switches and activate one with Enter or Space. New puzzle creates another solvable pattern and resets the move counter. It may be easier or harder than the previous pattern.