Light Up
Light Up is a logic puzzle on a grid of white cells and black walls. Place bulbs in white cells so that every white cell is lit. A bulb lights its whole row and column until a wall stops the light, no bulb may shine on another bulb, and a numbered wall has exactly that many bulbs directly beside it.
How to play
Easy puzzles are 7×7, Medium 8×8, and Hard and Expert 10×10. Every puzzle here has exactly one solution that logic alone reaches, and its level is set by the hardest technique it needs.
- Every white cell must be lit, by a bulb on it or by a bulb in its row or column with no wall in between.
- A bulb's light stops at the first wall.
- No bulb may stand in another bulb's light.
- A numbered wall has exactly that many bulbs directly above, below, left or right of it; a plain wall can have any number.
Playing on this site
- Tap a white cell to place a bulb, tap again for a dot that marks it as bulb-free, and once more to clear it.
- Drag across cells to paint the same mark along the way; the whole drag is one undo step.
- With a keyboard, use the arrow keys to move and Space to cycle the mark.
- Lit cells are tinted, so dark ones stand out. A number dims once its bulbs are all placed and turns red if it has too many.
- Dots are only a helper: the puzzle is solved as soon as every bulb is in place.
- Hint points out misplaced bulbs and dots first, then names the next technique and highlights where it applies.
- Your puzzle is saved in this browser, so you can come back to it later.
Techniques by level
Every technique the solver knows, from easiest to hardest. A puzzle's level is the hardest one it needs.
Easy
- Already lit
- This bulb lights its row and column up to the walls. No other bulb may stand in that light.
- Number complete
- This wall already has as many bulbs beside it as its number, so its other sides stay dark.
- Number needs all
- This wall needs a bulb on every side still open.
- Only one way to light
- The highlighted cell is dark and only one cell can still light it, so that cell gets a bulb.
Medium
- Around a number
- Every way to put this wall's bulbs agrees on the marked cells, for example by always lighting them.
Hard
- Would leave a dark cell
- A bulb here would block every way to light another cell, or a number's last spots. So it stays empty.
Expert
- Contradiction
- Assume the opposite in the marked cell and a rule breaks a few steps later. So it can only be this.
Questions
How do I start a Light Up puzzle?
Start with the numbers. A 0 means no bulb on any side, so dot those cells. A 4 needs bulbs on all four sides, and a 3 next to the edge or another wall often has only three free sides left. Each bulb you place lights its row and column, so dot every cell it shines on.
Will I ever have to guess?
No. Every puzzle has exactly one solution that logic alone reaches, at every level.
Is Light Up free to play here?
Yes. Every level is free, with no account and no sign-in.