Lights Out

Lights Out is the classic 5×5 light-toggling logic puzzle. Click cells to toggle them and their 4 neighbors. Turn off every light to win.

About Lights Out

Lights Out is an electronic puzzle invented by Tiger Toys in 1995. The board is a 5×5 grid of buttons that can each be on (lit) or off (dark). Pressing any button toggles itself plus its 4 orthogonal neighbors (up, down, left, right). The puzzle starts with a random arrangement of lit buttons; your goal is to turn them all off. Lights Out is a perfect puzzle for teaching linear algebra over GF(2): every solvable position can be uniquely solved by pressing each button at most once, in any order. The minimum number of presses to solve any 5×5 Lights Out position is at most 15. Our puzzles always start solvable.

How to Play Lights Out

1. Click any cell to toggle it. The cell and its 4 orthogonal neighbors all switch state (on becomes off, off becomes on).
2. The puzzle starts with some lights on. Your goal is to turn off ALL lights — every cell should be dark.
3. You can click cells in any order. Each press is just a toggle, not a destructive move.
4. The Moves counter tracks how many clicks you have used. Lower is better.
5. Press New puzzle to scramble and start over.

Tips and Strategy

• Use the “chase the lights” technique: starting from the top row, press cells in row 2 to turn off lit cells in row 1. Continue down to clear each row.
• After chasing to the bottom row, the bottom row reveals the solution pattern. Specific bottom-row patterns require specific top-row “openers”.
• Memorize the 7 standard top-row openers that lead to solved boards after chasing.
• Order does not matter. You can press cells in any sequence and the result is the same.
• Each cell only needs to be pressed 0 or 1 times. Pressing twice cancels.
• On 5×5 boards, the optimal solution always uses at most 15 presses.
• When stuck, restart and try chasing again. Most failures come from mis-tracking the chase.

History and Origin

Lights Out was invented by Avi Olti, Gyora Benedek, Zvi Herman, Revital Bushinsky, Avraham Reichental, and Yuda Yodfa, and released by Tiger Toys in 1995. It became a hit handheld electronic puzzle and inspired numerous video game adaptations. The puzzle has deep mathematical structure: solving it is equivalent to solving a linear system in modular arithmetic. Mathematicians have proven exactly which 5×5 arrangements are solvable (most are) and that the maximum solution length is 15 button presses.

Variations and Game Modes

Variants include 4×4 boards (smaller, easier), 6×6 and 7×7 boards (larger, more solutions), Lights Out Cube (5×5 on each face of a cube), Lights Out Deluxe with multiple light states, and Merlin (an early electronic puzzle with similar mechanics).

Frequently Asked Questions

How do you solve Lights Out?

Use “Light Chasing”: from the second row down, press each cell whose neighbor in the row above is lit. After clearing rows 1-4 this way, the bottom row reveals what cells you needed to press in the top row. Restart with the corrected top-row opener.

Is every Lights Out puzzle solvable?

On a 5×5 board, exactly 7/8 of all possible starting configurations are solvable. Our puzzle generator only produces solvable puzzles, so you will never face an impossible board.

How does the toggle work?

Pressing a cell flips that cell AND its 4 orthogonal neighbors (up, down, left, right). Diagonal cells are NOT affected. Cells on edges or corners have fewer neighbors to toggle.

Does the order of presses matter?

No. Lights Out is “commutative” — the order in which you press cells does not change the final state. Only WHICH cells you press matters, not when.

How many presses are needed in the worst case?

On a 5×5 board, no Lights Out puzzle requires more than 15 button presses to solve. Most puzzles can be solved in 8-12 presses.

Why do I sometimes have one or two lights left?

You probably mis-applied the chasing technique. After chasing to the bottom, if there are leftover lights, the standard technique is to memorize the corresponding top-row “openers” that fix specific patterns.

Is Lights Out related to other puzzle types?

Yes. Lights Out is mathematically equivalent to solving a system of linear equations over GF(2) (modulo 2 arithmetic). It is studied in algebra courses and computer science.

Can children play Lights Out?

Yes, but the optimal strategy requires abstract thinking. Kids can enjoy clicking buttons and watching patterns, but methodically solving Lights Out usually takes age 10+ to grasp.