The fastest way to get better at Light Up is to start from the numbers, dot everything a bulb lights, and look for dark squares that only one place can still light. We measured these tips on all 150 of the game’s levels, and the numbers below come from those tests.
These build on how to solve Light Up. If you haven’t played before, start with the rules.
Solving tips
1. Start with the 0s
None of the squares touching a 0 can have a bulb. A 0 is the first move on 38 of the 50 Easy levels, 45 Medium and all 50 Hard.
2. Then the numbers with just enough room
A 4 always has bulbs on all four sides. So does any number with exactly as many white squares beside it as it needs: a 3 on an edge, a 2 in a corner, a 1 hemmed in by black squares. Look for them next: on the game’s levels, that’s 3.5 steps per Easy level on average, 6.6 on Medium and 8.2 on Hard.
3. Dot everything a bulb lights
Every bulb rules out its whole row and column. On the game’s levels, 60% of all steps on Easy and Medium rule squares out rather than place a bulb, and 66% on Hard. The dots are how you see where light can still come from.
4. Work around the numbers
Most bulbs end up next to a number: 73% of the bulbs on the Easy levels, 72% on Medium and 70% on Hard. When you’re not sure where to look, look beside the numbers that still need bulbs.
5. Find the dark squares in tight spots
A square boxed in by black squares and dots often has only one way left to be lit, sometimes only by a bulb of its own. That’s 3.5 steps per Easy level on average, 6.4 on Medium and 10 on Hard.
6. Watch the diagonals of 3s
A bulb diagonal to a number lights two of its squares at once. Next to a 3 in the open, or a 2 with three squares still open, that leaves too little room, so the diagonal gets no bulb. It’s needed on 19 of the 50 Easy levels, 27 Medium and 49 Hard.
Tips for playing on PeerPuzzles
7. Tap to cycle, right-click to go back
Tap a square once for a bulb, again for a dot, and again to clear it. On a computer, right-click cycles the other way, Ctrl/Cmd + Z undoes a move, and H asks for a hint.
8. Let the light and Stuck? help
Lit squares glow as you place bulbs, so dark squares stand out. Bulbs that light each other are ringed in red, a number turns red when it can’t be met, and it dims once it has all its bulbs. If you’re stuck, Stuck? points at the next bulb and the squares to look at, showing the squares ruled out on the way as faint dots, without placing anything for you. If a bulb or dot is wrong, it rings that square first.