Is there a puzzle where you switch all the lights off?

Switch Off, one of the puzzles in Games by Zaweba, is built around exactly that idea. It has fifty glowing 5 by 5 bulb puzzles, and pressing a bulb flips it on or off along with the bulbs directly above, below, left and right of it. Turn every bulb off and the level is solved. The app is free and works offline.

The puzzles come in sets of ten levels, and the challenge is not just to solve each one but to do it with as few presses as you can.

What one press does

The rule is simple and the consequences are not. A press on a bulb in the middle of the board changes five bulbs: itself and its four neighbours. A press on an edge changes four, and a press in a corner changes three. Diagonal neighbours are never touched. So clearing one bulb almost always lights up others, and the puzzle is finding the presses whose side effects cancel out.

Two things help to know. Pressing the same bulb twice puts everything back as it was, so a press is either needed or it isn't. And the order of the presses makes no difference to the final board. Those two facts turn a confusing tangle into a question of which bulbs to press, not when.

Gold, par and the fewest presses

Each level has a par: the fewest presses possible. Solve it in that number and you earn gold. That gives every level two goals. The first is simply to get the board dark, by any route. The second is to come back and find the tidy solution, which usually means spotting that some of your presses were cancelling each other out.

A useful method for the second goal is to work down the board row by row. Look at the lit bulbs in the top row and press the bulb directly beneath each one; that clears the top row without touching anything above. Carry on down. When you reach the bottom you will often have a few bulbs left, and that pattern tells you which top-row presses you should have made at the start. Try those, chase down again, and the board clears.

Controls and helpers

Click a bulb with the mouse to press it. The panel beside the board picks levels, and the Left and Right keys move between them. Z undoes a press, R restarts the level, and H gives a hint when you are stuck. Because a press can always be undone, there is no harm in experimenting: press, look at what changed, and undo.

Finding it in the library

Switch Off is on the Puzzles shelf of Games by Zaweba, alongside Picture Grid, Slide Puzzle and Marble Solitaire. Type its name in the search box with Ctrl+F to jump to it, or star the tile so it waits in Favourites. The title card explains the rules before you start, and F1 explains them again whenever you need it.

Plays and best results are kept on the tile, in a scores file on your own PC. There are no adverts and nothing to sign up for, so it is the kind of puzzle you can open for five minutes and close again with a level or two solved, then pick up where you left off another day.