Read the complete cross before pressing
A press is not an instruction to turn a square off. It reverses every light in a fixed local pattern, so some lights may turn on while others turn off.
LEARNING CENTRE
Cross Lights: understand the effect of a press
Turn every light off by reasoning about toggles rather than chasing whichever lights look inconvenient. These lessons use the five-by-five Cross Lights rule: a press flips its own square and its horizontal and vertical neighbours, with no wrapping at the edges.
Rules you need at the board
Switch every light off. Pressing a square flips that square and its horizontal and vertical neighbours. Edges do not wrap and diagonals do not change. The fixed challenges stop when solved. The prediction drills describe toggle operations even when an intermediate pattern is dark.
Four techniques to practise
Two identical toggles cancel
Repeated presses can be simplified before you perform them. What matters for each button is whether it is pressed an odd or even number of times.
The final pattern does not depend on press order
Overlapping crosses may look as if they interfere unpredictably. In fact, each cell only needs a count of how many selected presses affect it.
Chase lights downward without undoing finished rows
Row chasing replaces scattered experiments with a repeatable test. First choose which buttons, if any, to press in the top row. The remaining rows can then be processed systematically.
Follow a practice collection
1. Predict a press before making it
Compare corner, edge and interior crosses, then simplify repeated presses. Judge the predicted light pattern separately from the number of moves used.
2. Compare sequences by their effect
Trace overlapping crosses and reorder planned presses. Use cancellation and odd-or-even toggle counts to explain why different sequences can finish at the same pattern.
3. Test a complete row-chasing plan
Make a first-row choice, chase each resulting row and inspect the final row. Distinguish a valid full solution from a failed starting choice and from an unproved claim of minimum moves.
What the explanations can establish
Cancellation and order independence describe the toggle operations. The live game stops accepting moves when the board is solved, so a comparison that passes through a solved state belongs in a practice sandbox. Row chasing tests a chosen first-row pattern; it does not guarantee that an arbitrary choice works or produces the fewest moves. A solvable board can have more than one solution.
Hints in this study area use the current marks. In Nonograms, Tents and Bridges, deductions assume earlier marks are correct; a local conflict stops the suggested step, but absence of a warning does not certify every mark. Minefield flags are never used as evidence. Cross Lights tests complete first-row choices and verifies the resulting plan.
Keyboard: Tab to controls and press Enter or Space. Board state saves locally; no account is needed.