A more deliberate way to solve Crosslight

A tempting first approach is to press whichever tile removes the most green lights. That can work for a move or two, but a useful move may temporarily add lights. Crosslight rewards thinking about the effect of a group of moves rather than the appearance of one intermediate board.

Start with reversibility

Every move reverses itself. Pressing the same tile twice brings the board back to exactly where it was. This means you do not need to include the same tile more than once when describing a final solution: two presses cancel, three are equivalent to one, and four cancel again.

Try this on the board. Select a centre tile, note the changes and select it again. Then restart so that your next experiment begins from a known arrangement.

Try two moves in different orders

Select one tile and then a neighbouring tile. Remember the result, restart, and select them in reverse order. The final board is the same. A tile affected by both moves flips twice regardless of which move came first.

This lets you think of a solution as a set of tiles to press. The order may make your reasoning easier to follow, but it does not change the final result of that set.

Work down the board

Once you decide which tiles to press in the top row, look at the lights left on there. Press the tile immediately below each of those lights. That fixes the first row. Continue downward: use row three to clear row two, row four to clear row three and row five to clear row four.

At that point, the bottom row either clears or it does not. If it does not, the initial top-row choices need to change. With five tiles in the top row there are 32 possible subsets of initial presses, including pressing none. Trying each subset and then following the row-clearing rule is a finite method for finding a solution to these solvable boards.

Keep an experiment small

Write down just the top-row subset and whether the bottom row cleared. Restart between trials instead of mixing one unfinished attempt into the next. You can also use Undo to inspect the effect of a move, but a written record makes systematic trials easier.

You do not have to use this method to enjoy the game. Pattern spotting and experimentation are valid approaches too. The aim is to understand why a move helps, not merely to make the current count of green lights smaller. Try the method in Crosslight.