Black Box Lasers
Black Box Lasers is a deduction puzzle about things you cannot see. A few balls sit somewhere inside a dark square, and the only way to find them is to send beams in from the edge and study what happens.
James Harvey wrote this version for Simon Tatham's Portable Puzzle Collection, based on an older board game. It loads in a regular browser tab and needs no download, so it works fine on a laptop, tablet or phone.
How to play Black Box Lasers
The grid is ringed by edge squares. Pick one and a beam travels straight into the box. If it meets a ball head-on, it is absorbed and the edge square shows H. If a ball sits diagonally ahead, the beam turns away from it by ninety degrees. A beam that ends up leaving through the square it entered shows R.
Every other beam exits somewhere else, and both its entry and exit squares get the same number. Fire as many beams as you like, but each one is a clue you have to explain.
Mark the spots where you think the balls are by clicking inside the box. When the number of marks matches the number of balls, a check button shows up at the upper left. Use it to test your layout against the real one.
Controls
| Action | Keyboard | Mouse | Touch |
|---|---|---|---|
| Fire a beam | Arrow keys to an edge square, then Enter | Left-click an edge square | Tap an edge square |
| Mark or unmark a ball | Arrow keys inside the box, then Enter | Left-click inside the box | Tap inside the box |
| Lock a square, row or column | Space | Right-click | Press and hold |
| Submit your guess | Move to the corner button, then Enter | Click the top left button | Tap the top left button |
| Undo, redo, new puzzle | U, R, N | — | — |
Tips
- Start with beams through the middle rows. Long paths cross more of the box, so one shot can rule out many squares at once.
- An R on an edge square next to a corner often means a ball sits just inside, one step diagonal from where the beam started.
- When a beam goes straight across with matching numbers on opposite sides, every square on that line is empty. Lock that row so you stop second-guessing it.
- Trace each numbered path by hand before marking. If your marked balls would not bend the beam the same way, the layout is wrong.
- Fire a final beam through any area you have not tested yet before pressing the check button.
If you like Black Box Lasers, try these
Undead Mirror MazeMirrors bend the sightlines here too, and you work out which monsters sit in each cell from the counts along the edges.
Crater SpaceHidden targets again, but you fire paint missiles at a moon grid to find three cloaked ships in as few shots as possible.
Questions
How many balls are hidden in Black Box Lasers?
The standard 8x8 box holds five, and the status bar tracks how many you have marked. The Type menu offers smaller and larger boxes with different ball counts.
What happens if my guess is wrong?
The puzzle points out one piece of evidence against you, either by circling a beam your layout cannot produce or by revealing a new beam in red. You can then adjust your marks and try again.
Can I play Black Box Lasers on a phone?
Yes. Tapping acts as a left click and pressing and holding acts as a right click, so firing, marking and locking all work by touch.
More like this: all puzzle games · Math games · every game A–Z
