Master Light Up (Akari) puzzles with step-by-step techniques.
Whether you are brand new to the light up puzzle (also known as Akari) or you have been solving them for years, this guide walks you through every technique you need. By the end, you will know how to solve even the trickiest grids with confidence — and you can practice free on GridPaw to sharpen your skills.
A light up puzzle is played on a rectangular grid of white and black cells. Your goal is to place light bulbs (we call them cats 🐱 on GridPaw) on white cells so that:
That is the entire ruleset. The beauty of this logic puzzle is that those four rules create surprisingly deep deduction chains. Let us learn the strategy to crack them.
When you first look at a light up puzzle, scan for any black cell marked 4. This is the most powerful starting point because the deduction is immediate and absolute.
A cell with the number 4 has exactly four orthogonal neighbors (up, down, left, right). Since it requires exactly 4 adjacent cats, every single white neighbor must contain a cat. Place them all right away — no thinking required.
After placing those cats, mark the cells they illuminate. Each cat lights its entire row and column until blocked by a black cell. This single step often illuminates a large portion of the grid and gives you a strong foothold for the rest of the solve.
Pro tip: Even if you do not see a 4, look for cells close to corners or edges. A corner cell only has 2 neighbors, so a "2" in a corner is just as decisive — both neighbors must be cats.
The opposite extreme is equally useful. A black cell marked 0 means none of its adjacent white cells can hold a cat. Mark all of those neighbors with an X (or a dot on GridPaw) to indicate "no cat here."
Why does this matter? Because every X you place reduces the number of candidate positions for cats. In a tight light up puzzle, eliminating even one cell can cascade into forced placements elsewhere. The grid shrinks mentally, and the solution path becomes clearer.
After handling 0-cells, check whether any remaining numbered cells now have most of their neighbors eliminated. If a "3" cell has three X-marked neighbors and only three open spots left, all three open spots must be cats — the same logic as the number-4 trick, just triggered by elimination rather than the grid edge.
Line-of-sight is the core mechanic that makes Akari unique among logic puzzles. Once you place a cat, it illuminates every white cell in its row and column until a black wall blocks the beam. This has two critical consequences:
The strategy here is iterative: place a cat → mark its illumination → check which cells are still dark → find cells that can only be lit from one direction → place more cats. Each pass through this loop resolves more of the grid.
Pay special attention to cells near black walls. A dark cell sandwiched between two black cells in its row can only be lit vertically — that is a forced placement waiting to be discovered.
A forced placement happens when a white cell can only be illuminated from exactly one direction. This is the bread-and-butter strategy for solving a light up puzzle after the obvious number-cell deductions are done.
Here is how to spot them:
Sometimes you will find a cell that can be lit from two directions, but one of those directions would leave another cell permanently dark. That is a deeper form of forced placement — it requires looking one step ahead. As you practice on GridPaw, you will develop an intuition for these patterns.
Another powerful variant: if two dark cells share the same single remaining light source, that source is doubly forced. Look for clusters of dark cells that funnel down to one cat position.
Sometimes the direct techniques above are not enough, especially on harder Akari puzzles. That is when you use elimination — a form of proof by contradiction.
The idea is simple:
This technique is also called " bifurcation" or "guess-and-check" by puzzle enthusiasts. While purists prefer to avoid it, it is a legitimate and sometimes necessary strategy for the hardest grids. The key is to choose cells where the consequences propagate quickly — a cell adjacent to a numbered wall is ideal because the number constraint immediately tells you if something is wrong.
Tip: Always check the easier techniques first. In well-designed puzzles (like those on GridPaw), elimination is rarely needed until the final stages.
Even experienced solvers fall into these traps. Watch out for them as you work through any light up puzzle:
They are the same puzzle. "Light Up" is the English name used by most puzzle publishers, while "Akari" (明かり, meaning "light" in Japanese) is the original Japanese name coined by Nikoli, the publisher that popularized it. On GridPaw, we use "Light Up" but the rules and strategy are identical.
Well-constructed light up puzzle grids always have exactly one valid solution. If you find yourself making a guess with no logical basis, step back — there is almost certainly a deduction you missed. Every cell should be determinable through pure logic. If you reach a point where two configurations both seem valid, re-examine the numbered cells and line-of-sight constraints more carefully.
Yes! Every properly designed Akari puzzle is solvable through pure deduction. The five steps in this guide — number-4 cells, number-0 cells, line-of-sight, forced placements, and elimination — cover all the logical techniques you need. The elimination technique (Step 5) might feel like guessing, but it is actually a formal proof method: you are not randomly trying options, you are testing a hypothesis and looking for contradictions.
Start with 7×7 or smaller grids. These typically use only the basic techniques (Steps 1–3) and can be solved in a few minutes. Once you are comfortable, move to 10×10 grids which introduce forced placements (Step 4). The largest grids (15×15 and above) may require the full elimination technique. GridPaw offers puzzles across all difficulty levels, so you can progress at your own pace.
