Lights #717 · 6×6

• 6×6board
• 20lights on
• 11presses to solve
• 36cells

Lights #717 is a 6×6 board at medium level. It starts with 20 of its 36 lights on, and the one solution needs 11 presses.

Row 4 is the brightest, with 5 lights on. If you chase from the top, that is where most of the work happens.

2 corner lights are on. A corner light has only two neighbours, so it is changed by just three presses: itself and the two lights next to it.

With 11 presses in the solution, chasing from the top down and fixing the first row from what is left at the bottom is safer than trying to see the answer at once.

On medium boards, chase the lights down row by row, then use what remains at the bottom to decide the presses in the top row.