Light Up / Akari
Why are two bulbs invalid in Light Up?
Bulbs illuminate along rows and columns until a black cell blocks the light. Two bulbs may not illuminate each other. Numbered black cells count bulbs only in their four edge-adjacent cells.
Worked example
Two bulbs in one clear row conflict even with several empty cells between them. A black cell between them blocks that conflict.
What to check on your board
Apply the rule above to your current board, then verify the remaining puzzle constraints. The example explains a local deduction; it is not a solution to every randomly generated board.
Checking your next move
From a proposed bulb, follow all four straight sightlines until a black cell or the border. Any bulb already on those lines is a conflict. Then count bulbs beside each numbered black cell using edge neighbours only; illumination and numbered adjacency are different checks.
Using this reference
For Light Up / Akari, read the rule and the worked example together before opening the game. Separate what the rule explicitly requires from what only seems likely on the current board. A useful next move is one you can explain from the visible constraints, not merely a pattern that looks familiar.
If you get stuck, isolate a smaller part of the position and list what is still possible there. After a move, check the affected rows, regions or connections again. The reference explains the documented rules; progress, controls and save behavior belong to the linked game.
Read the developer’s manual ↗ · Open the developer’s browser version ↗
Manual inspected: · Simon Tatham & contributors · MIT