A toggle-the-grid logic puzzle stacked into a tower, black out every cell, then climb to a bigger, harder board.
Each board starts with a scatter of lit cells. Tapping a cell flips it and its orthogonal neighbours between light and dark. Your goal is to plunge the entire grid into darkness. Clear a board and you ascend to a larger one, so the puzzles grow as you climb.
Tapping a cell to flip it and its orthogonal neighbours, aiming to switch the whole grid off, is Lights Out — released by Tiger Electronics in 1995, with Parker Brothers' Merlin playing a similar game on a 3×3 grid two decades earlier.
The original structure is the climb: clear a board and ascend to a larger one.
Lights Out is a fixed 5×5, and that matters more than it sounds — the puzzle is linear algebra over two elements, and the size determines which starting patterns are solvable at all. Growing the grid therefore does not just add cells; it changes the mathematics you are solving under.
Umbra is an original free browser game that turns the classic cell-toggling light puzzle into a tower climb, with each cleared grid unlocking a larger and more demanding board.