💡 Lights Out: how one tap changes a whole board
Lights Out looks like a tapping game, but every move affects several places. The secret is to watch the group of squares that changes, not just the light you tapped.
What changes with each tap?
The light you tap and its direct neighbors switch: on becomes off and off becomes on. In a corner three lights change, on an edge four, and in the middle five. Diagonal lights do not change.
Two taps cancel each other
Tap the same square twice and every light it touched goes back to how it was. The order of taps does not change the final result either. So you can think about choosing a set of squares, not a long string of guesses.
Work row by row
One way to test options is to decide what to tap in the top row, then use the row below to turn off the lights above it. Not every first choice works; if a light is left at the bottom, try another one. The game also has a hint that works out a solution from the current board.
Questions and answers
Can every board in the game be solved?
Yes. All 220 boards are made by legal taps on a dark board and checked by a solver. Sizes go from 3x3 to 6x6.
Can I tap a light that is already off?
Yes. Sometimes that is exactly the move you need to turn off its neighbors. The goal is the whole board, not turning off one light at every step.