How to Play Light Up Puzzles

Light Up Rules

Light up puzzles (also called Akari, from the Japanese word for lamp) are played on a rectangular grid of white cells and black walls. You place light bulbs on white cells. A bulb shines along its row and column in all four directions until the light is stopped by a black wall, and the goal is for every white cell to be lit, either by a bulb on it or by a beam reaching it. Two bulbs may never see each other: if nothing blocks the way between them, the placement is illegal.

Some black walls carry a number from 0 to 4. The number states exactly how many bulbs sit in the white cells directly above, below, left and right of that wall; unnumbered walls give no information. A 0 wall touches no bulbs at all, so all four of its neighbors are instantly barred.

Solving is pure deduction. Satisfied numbers bar their remaining neighbors, cells with a single possible light source force a bulb, and every bulb you place crosses out entire row and column segments. The grid narrows until the last bulb clicks into place. A well-formed light up puzzle never requires guessing, and every grid on this site is machine-checked against that promise.

Step-by-Step: Solving a Light Up

1. Scan the numbered walls first. A 4 in the open, a 3 in a corner, or any number equal to its white-neighbor count places bulbs immediately.
2. Mark the bans. Every placed bulb bars the rest of its row and column segment; every satisfied number bars its remaining neighbors. Cross these cells out.
3. Find forced lights. Look for white cells that can only be lit from one position left; that position gets a bulb, which starts the next wave of bans.
4. Keep the beam bookkeeping. A cell is lit when any bulb shines on it; re-verify walls and unlit cells after every placement.
5. Finish by elimination. The last white cells usually have exactly one legal bulb spot each; place them and the whole grid glows.

Light Up Tips & Techniques

• Start from the big numbers. A wall marked 3 or 4 in a corner or along an edge has so few neighbors that most of its bulbs are forced immediately.
• A wall whose number equals its count of white neighbors fills them all: if the 2 is satisfied, every other neighbor is guaranteed bulb-free.
• Hunt for cells with a single source of light. If a white cell can only be lit from one remaining position, that position must hold a bulb.
• Cross out what bulbs cannot reach. Once a cell is lit, every other cell in its row and column segment is barred from holding a bulb; mark it and move on.
• Recheck the walls after every placement. Each new bulb changes the counts around up to four numbered walls, and a wall that just reached its number forbids the rest of its neighbors.

Frequently Asked Questions