Lantern Grid for beginners: place bulbs, read walls and light every cell.
Play a fixed first illumination puzzle, follow a six-bulb solution, and test why exact wall numbers alone do not finish the board. Includes reversible mistakes and keyboard controls.
A bright square is not necessarily a bulb. That distinction is the first thing to learn in Lantern Grid: you place the light sources, and the game shows where their straight beams reach. Your job is to illuminate every white cell while respecting numbered walls and keeping bulbs out of one another’s sight. This lesson supplies a fixed first board, a complete route and two checks you can reproduce.
Read the board before placing a bulb
Choose Practice this example beside the article, or Load beginner board in the game. Confirm Toggles 0 and this five-by-five layout. A dot is a white cell. A printed digit is a dark wall, including zero. Rows run top to bottom and columns left to right; R4C2 means row 4, column 2.
· · · · 0 1 0 · · 1 · 2 · 1 0 3 · · 0 · · · 0 · ·
There are fifteen white cells and ten numbered walls. White cells are the places you can edit; walls stay fixed. On the live board, ● means a bulb, + means a lit empty cell, and · means a dark empty cell. Accessible labels say whether a cell contains a bulb or is empty and lit or dark.
The three conditions for a finished puzzle
- Light every white cell. A bulb lights its own cell and sends light horizontally and vertically through white cells. The beam stops at the first wall or the outer edge. It cannot turn a corner. Any numbered wall blocks light too.
- Make each wall number exact. A wall marked 2 needs exactly two bulbs in its side-adjacent white cells. Diagonal bulbs do not count. A zero allows no adjacent bulb, although the white cells beside it must still be illuminated from somewhere else.
- Keep bulbs out of each other’s sight. Two bulbs cannot occupy the same uninterrupted row or column segment. A wall between them blocks the view. Light beams may overlap on an empty cell; that overlap is allowed.
Adding a bulb establishes a persistent light source. Removing that bulb removes only its contribution. A cell can stay lit if a second bulb still reaches it. There is no minimum bulb count or fastest-time requirement.
Learn the controls on the exact example
Click or tap a white cell to add a bulb; activate that same cell again to remove it. Each accepted change adds one to Toggles, even if it was a wrong guess. The game allows mistakes so you can inspect and undo them. Walls cannot be edited.
Check lighting tests the current pattern and adds no toggle. It reports dark cells, mismatched wall counts and visible bulb pairs. All three counts must be zero for a win. The live illumination total helps you see the effect of a move, but it does not check every condition automatically.
Tab reaches white cells and controls. Enter or Space toggles a bulb. Arrow keys move focus to the next white cell in that direction, skipping walls and stopping at the edge without wrapping. Undo last toggle reverses one edit, including after a win. Retry this board clears the whole attempt while keeping the clues.
Place four bulbs and inspect what is still missing
Start at the wall marked 3 at R4C1. It has exactly three side-adjacent white cells: above at R3C1, right at R4C2 and below at R5C1. All three need bulbs. The wall separates those bulbs’ sight lines, so their apparent proximity is allowed.
The wall marked 1 at R2C5 has only one adjacent white cell, R2C4; its other in-grid neighbours are walls. Put a bulb at R2C4 as well. Now predict whether the puzzle is finished before checking. Every numbered wall is exact at this point, but illumination is a separate requirement.
Reveal the four-bulb checkpoint and why it is not a win
After bulbs at R3C1, R4C2, R5C1 and R2C4, Toggles is 4. Exactly 8 of 15 white cells are lit. Check lighting reports 7 dark cells, 0 mismatched wall counts and 0 visible bulb pairs. The board stays editable because not every white cell is illuminated.
The seven dark cells are R1C1, R1C2, R1C3, R3C3, R4C5, R5C4 and R5C5. A satisfied number counts adjacent bulbs only; it says nothing about remote dark cells. The zero walls are satisfied with no bulb beside them even when some of their neighbours are still dark.
Complete your first board
Retry before comparing the full route below, so each toggle count starts from zero. Activate each listed white cell once. If you Check lighting between steps, the check adds no extra toggle. Every checkpoint in this route has 0 visible bulb pairs.
- R3C1: place the bulb above the 3. Toggles 1; 1 of 15 cells lit; 4 wall counts mismatched.
- R4C2: place the bulb to the right of the 3. Toggles 2; 4 cells lit; 3 wall counts mismatched.
- R5C1: place the bulb below the 3. Toggles 3; 5 cells lit; 2 wall counts mismatched.
- R2C4: supply the 1 at R2C5. Toggles 4; 8 cells lit; all wall counts exact.
- R1C3: send light across the top row and down column 3. Toggles 5; 12 cells lit; all wall counts exact.
- R5C5: light the lower-right corner and its two white neighbours. Toggles 6; all 15 white cells lit.
Press Check lighting after the sixth toggle to register the win. It reports zero in all three categories, locks the fifteen white-cell buttons and moves focus to Undo last toggle. A complete-looking pattern alone does not register the checked finish.
Reveal the finished map, wall counts and two short self-checks
+ + B + 0 1 0 + B 1 B 2 + 1 0 3 B + 0 + B + 0 + B
B marks a bulb in this paper map; + marks an illuminated empty cell. The ten wall counts are: R1C5 = 0, R2C1 = 1, R2C2 = 0, R2C5 = 1, R3C2 = 2, R3C4 = 1, R3C5 = 0, R4C1 = 3, R4C4 = 0 and R5C3 = 0. Each matches its printed digit. All fifteen white cells receive light, and no two of the six bulbs see each other. Independent enumeration confirms exactly one valid bulb pattern for this clue set.
Why can R1C4 be lit beside a zero? The bulb at R1C3 reaches it across the row. The zero at R1C5 forbids placing a bulb at R1C4, not illuminating that cell. Light at R1C4 then stops at the zero wall; it does not continue through the wall.
What changes if you Undo after the win? The last bulb at R5C5 disappears, restoring Toggles 5. The board reopens. R4C5, R5C4 and R5C5 become dark. A check gives 3 dark cells, 0 mismatched wall counts and 0 visible bulb pairs. Activate R5C5 again and Check to finish, or Retry to return to the original zero-toggle board.
Reproduce a visible-bulb mistake
Retry and put bulbs at R1C1 and R1C3. Both are legal cells to edit, and the interface accepts both toggles. There is no wall between them along row 1, so the bulbs shine on each other. Check lighting reports 8 dark cells, 4 mismatched wall counts and 1 visible bulb pair at Toggles 2. Bright cells do not make that pair permissible.
Undo once removes R1C3 and leaves the earlier R1C1 bulb at Toggles 1. That earlier bulb was a trial, not part of the correct answer. Retry before replaying the six-step solution. An accepted edit is not a hint, and undoing the latest error does not guarantee that every older choice was correct.
Retry the same lesson or start another round
Load beginner board restores these exact clues. Its practice address reloads this board after refresh, without saving bulbs or history. New puzzle moves through five original prepared boards, then repeats; it clears the practice address. There is no random generation, countdown, login, payment or advertisement action required. Your attempt stays in the current browser tab.
This introduction teaches the implemented rules on one small board. It does not guarantee that every larger illumination puzzle has a short forced route or that every puzzle encountered elsewhere has a unique answer. Check all three conditions rather than treating a bright display, exact numbers or a low toggle total as sufficient.